Method and system for determining safe return mileage

Abstract

The present application relates to a method and system for determining a safe return distance. This application discloses a method for determining and displaying an area comprising a plurality of locations that a person or vehicle can reach from a departure node or current location while still reaching a destination node or home location, assuming that a parameter constraining the distance traveled by a person or vehicle at the departure node or current location has an initial value. The method can be implemented on a mobile device such as a portable navigation device and / or a server or computer, or can be provided as a computer program product.

Description

[0001] Information about divisional applications

[0002] This application is a divisional application. The parent application is an invention patent application filed on May 4, 2017, with application number 201780027461.X, and titled “Method and System for Determining Safe Return Mileage.” Technical Field

[0003] The present invention generally relates to methods for determining an area within which one can travel when traveling between a departure node and a destination node. The present invention also extends to mobile devices, optionally portable navigation systems, systems, and computer program products for implementing such methods. The methods may be computer-implemented. Illustrative embodiments of the present invention relate to portable navigation devices (so-called PNDs), in particular PNDs that include global positioning system (GPS) signal reception and processing functionality. More generally, other embodiments relate to any type of mobile processing device configured to execute navigation software to provide route planning functionality and preferably also navigation functionality. Background Art

[0004] Portable navigation devices (PNDs) that include GPS signal reception and processing functionality are well known and widely used as in-car or other vehicle navigation systems.

[0005] Generally speaking, a modern PND includes a processor, memory (at least one of volatile and non-volatile, and typically both), and map data stored within the memory. The processor and memory cooperate to provide an execution environment in which a software operating system can be established, and it is common to also provide one or more additional software programs to enable control of the functionality of the PND and to provide various other functions.

[0006] Typically, these devices further include one or more input interfaces that allow a user to interact with and control the device, and one or more output interfaces by which information can be relayed to the user. Illustrative examples of output interfaces include a visual display and a speaker for audible output. Illustrative examples of input interfaces include one or more physical buttons for controlling on / off operation or other features of the device (the buttons need not be located on the device itself, but may be located on the steering wheel if the device is built into a vehicle); and a microphone for detecting the user's voice. In a particularly preferred arrangement, the output interface display can be configured as a touch-sensitive display (by means of a touch-sensitive overlay or otherwise) to additionally provide an input interface by which the user can operate the device by touch.

[0007] This type of device will also typically include: one or more physical connector interfaces by which power signals and (optionally) data signals can be transmitted to and received from the device; and (optionally) one or more wireless transmitters / receivers to allow communication via cellular telecommunications and other signal and data networks (for example, Wi-Fi, Wi-Max, GSM, etc.).

[0008] This type of PND device also includes a GPS antenna, by means of which satellite broadcast signals containing location data can be received and subsequently processed to determine the current location of the device.

[0009] PND devices may also include electronic gyroscopes and accelerometers that generate signals that can be processed to determine current angular and linear acceleration and, in turn, together with position information derived from GPS signals, to determine the speed and relative displacement of the device and, therefore, the vehicle in which the device is installed. Typically, such features are most commonly provided in in-vehicle navigation systems, but may also be provided in PND devices where advantageous.

[0010] The utility of such PNDs lies primarily in their ability to determine a route between a first location (usually a starting or current location) and a second location (usually a destination). These locations may be input by the user of the device by any of a variety of different methods, for example, by postal code, street name and house number, previously stored "well-known" destinations (e.g., famous places, civic venues (such as sports fields or swimming pools), or other points of interest), and favorite or recently visited destinations.

[0011] Typically, PNDs are implemented with software that calculates the "best" or "optimal" route between a starting address location and a destination address location from map data. The "best" or "optimal" route is determined based on predetermined criteria and is not necessarily the fastest or shortest route. The selection of a route along which the driver is guided can be highly complex, and the selected route may take into account existing, predicted, and dynamically and / or wirelessly received traffic and road information, as well as historical information.

[0012] Additionally, the device can continuously monitor road and traffic conditions and offer or select a route to take for the remainder of the trip as conditions change. Real-time traffic monitoring systems based on various technologies (e.g., mobile phone data exchange, fixed cameras, GPS fleet tracking) are being used to identify traffic delays and feed the information into notification systems.

[0013] This type of PND is typically mounted on the dashboard or windscreen of a vehicle, but may also form part of the onboard computer of the vehicle radio or indeed part of the control system of the vehicle itself. Navigation devices may also be part of handheld systems such as PDAs (portable digital assistants), media players, mobile phones, etc., and in these cases the normal functionality of the handheld system is extended by installing software on the device to perform both route calculation and navigation along the calculated route.

[0014] Route planning and navigation functionality can also be provided by a desktop or mobile computing resource running appropriate software. For example, the Royal Automobile Club (RAC) provides an online route planning and navigation facility at http: / / www.rac.co.uk that allows a user to input a starting point and a destination, calculates a route (aspects of which can be specified by the user) on a server to which the user's PC is connected, generates a map, and generates a set of detailed navigation instructions for guiding the user from the selected starting point to the selected destination. The facility also provides a pseudo-three-dimensional rendering of the calculated route and route preview functionality that simulates the user traveling along the route and thereby provides the user with a preview of the calculated route.

[0015] In the context of a PND, once a route has been calculated, the user interacts with the navigation device to select the desired calculated route, optionally from a list of suggested routes. Optionally, the user can intervene in or guide the route selection process, for example by specifying specific routes, roads, locations, or criteria to be avoided or mandatory for a particular journey. The route calculation aspect of a PND forms one primary function, and navigation along this route is another primary function.

[0016] During navigation along a calculated route, such PNDs typically provide visual and / or audible instructions to guide the user along the selected route to the end of the route (i.e., the desired destination). PNDs also typically display map information on the screen during navigation, with this information being regularly updated on the screen so that the displayed map information represents the current location of the device and, therefore, the current location of the user or the user's vehicle if the device is being used for in-vehicle navigation.

[0017] The icon displayed on the screen typically indicates the current device location and is located in the center, with map information for current and surrounding roads near the current device location and other map features also displayed. In addition, navigation information may optionally be displayed in a status bar above, below, or to the side of the displayed map information. Examples of navigation information include the distance from the current road the user needs to take to the next detour, the nature of which may be indicated by another icon suggesting a specific type of detour (for example, a left turn or a right turn). The navigation function also determines the content, duration, and timing of audible instructions by which the user can be guided along the route. As can be appreciated, a simple instruction such as "turn left in 100 meters" requires significant processing and analysis. As previously mentioned, user interaction with the device can be achieved by touch screen or, alternatively or additionally, by a steering column-mounted remote control, by voice activation, or by any other suitable method.

[0018] Another important functionality provided by the device is automatic route recalculation in the following situations: the user deviates from a previously calculated route during navigation (accidentally or intentionally); real-time traffic conditions indicate that an alternative route would be more favorable and the device is able to automatically recognize such conditions as appropriate; or when the user actively causes the device to perform route recalculation for any reason.

[0019] While route calculation and navigation functionality are fundamental to the overall utility of a PND, the device may be used for information display only or "free driving" purposes, wherein only map information relevant to the current device location is displayed, and wherein the device has not yet calculated any route and is not currently performing any navigation. This mode of operation is typically suitable when the user already knows the route they wish to follow and does not require navigation assistance.

[0020] Devices of the type described above provide a reliable means for enabling a user to navigate from one location to another.

[0021] Navigation users may often be concerned about how far they can travel in a vehicle given certain constraints. For example, in the case of conventional internal combustion engine vehicles, it is important for the user to know how far they can travel based on their current fuel load of gasoline, diesel, etc., or in the case of increasingly common electric vehicles (EVs), it is important for the user to know how far they can travel based on the amount of charge currently carried by the vehicle's battery. This concern is often referred to as "range anxiety," in which the user is concerned about reaching a destination (e.g., a home location or charging point) without getting stranded.

[0022] In simple terms, a 360-degree range based on the current vehicle position and fuel load can be displayed to the user on a map. For example, EP 0638887 A2 describes a method for calculating and displaying the range for a specific remaining fuel level. WO 2014 / 001565 A1 describes an improved method that also takes into account the route planning preferences of the navigation device. EP 1926074 A1 discloses a map display device that includes a search component for calculating travel time information about the travel time to any point reachable from a specific reference point (i.e., the current position of the user's vehicle).

[0023] However, these methods only display information related to the current reachable area relative to the device and do not provide any information about whether the user can reach a given road segment on the map and still reach the desired destination, assuming the current fuel load or other constraints. This can be referred to as the "safe return distance" between the current location of the device and the desired destination, assuming the current fuel load or other constraints.

[0024] Ideally, both the current reachable range and the safe return range (from which the destination is still reachable) relative to the vehicle would be maintained simultaneously, so that the two ranges could be displayed to the user together, or at least both immediately available for separate display to the user. Unfortunately, however, determining the area reachable from a given point is inherently computationally expensive. Calculating the safe return range may involve having to determine the reachable area for each of a large number of locations within the map area (e.g., all possible locations within the current reachable range), which is even more expensive. Therefore, the effort required to calculate both the current reachable area and the safe return range using conventional techniques is generally infeasible. This is especially true for mobile devices with limited processing power, such as a driver's smartphone.

[0025] Therefore, the present invention aims to provide an improved method and system for reducing so-called "range anxiety". Summary of the Invention

[0026] According to a first aspect of the present invention, there is provided a method for determining an area within which a person may travel when traveling between a departure node and a destination node, the method comprising:

[0027] determining or retrieving data indicating a first boundary enclosing a first area around the destination node, the first area representing a location from which a person or vehicle may travel to the destination node assuming a parameter has a first value, wherein the value of the parameter constrains a distance that may be traveled by the person or vehicle;

[0028] estimating a value of the parameter when the person or vehicle is at the first location other than the departure node and the destination node based on the initial value of the parameter at the departure node and an estimated change in value of the parameter associated with traveling from the departure node to a first location within the first boundary; and

[0029] The estimated value of the parameter at the first location is compared to the first value to determine whether the person or vehicle can reach the first location from the departure node while still reaching the destination node assuming the parameter has the initial value.

[0030] Embodiments allow determining whether any particular location can be reached from a departure node while still reaching a destination node, assuming a certain parameter at the departure node (whose value constrains the distance that can be traveled by a person or vehicle) has an initial value. The population of these locations thus represents an area within which a person or vehicle can travel while still reaching the destination node, and thus this determination can help reduce range anxiety for users.

[0031] Furthermore, and importantly, this determination can be made with relatively low computational overhead by a relatively simple comparison between the expected value of the parameter at a given location (e.g., a first location) after traveling from a departure node to the location and the value of the parameter associated with the boundary within which the first location is located. For example, if the expected value of the parameter at the first location determines that the destination node is reachable from the first location, then the first location is within the safe return range of the destination node. By way of example, where the parameter is the charge level of an electric vehicle, if the expected remaining charge level at the first location, which is within a first boundary, is 50%, and the first boundary indicates that only 10% of the charge is required to reach the destination node, then it is determined that the first location is reachable from the departure node while still reaching the destination node. Since the first area around the destination node is associated with a specific value of the parameter and is predetermined (i.e., determined or obtained in the initial step of the method), it is then only necessary to check whether the first location falls within the first area and compare the two values ​​as described above. It will be appreciated that the following determination can therefore be made directly via this comparison, without, for example, having to separately calculate the reachable area relative to the first location: whether, assuming the parameters have the initial values, the first location can be reached from the departure node while still reaching the destination node. This reduces the computational overhead of the method, particularly when the method is repeated to determine whether, assuming the parameters have the initial values, other locations can be reached from the departure node while still reaching the destination node.

[0032] A safe return distance comprising a plurality of locations that can be reached from a departure node while still reaching a destination node, assuming that the parameters have initial values, can therefore be determined relatively simply in a manner that can be implemented even on a mobile device with relatively limited processing power.

[0033] It will be understood that the term "safe return range" as used herein refers to the distance to a location that can be reached from a departure node while still reaching a destination node, assuming the parameters have initial values.

[0034] The value of the parameter constrains the distance that a person or vehicle can travel from a specific starting location. The first boundary therefore represents the maximum reachable point from which a person or vehicle can travel to the destination node, assuming that the parameter has the first value. Similarly, the multiple different boundaries around the destination node mentioned below represent the maximum reachable point from which a person or vehicle can travel to the destination node, assuming that the parameter associated with each of the different boundaries has a corresponding value. A specific boundary around a departure node can generally be constructed using multiple points around the destination node, wherein the points are interconnected to define the shape of the boundary. It will be understood that the boundary is not necessarily a complete continuous boundary around the destination node, for example, when the boundary is determined only along a specific direction relative to a specific node. It will also be understood that, when determining in real time, it may be impractical to determine the full extent of the boundary before the initial value of the parameter or the departure node changes.

[0035] In general, the distance that can be expected to be traveled may be constrained by one or more parameters, and the method may therefore take more than one parameter into account. However, typically only a single constraining parameter is taken into account.

[0036] Generally speaking, the method may involve a method for determining an area within which a user may travel when traveling between a departure node and a destination node based on digital map data, wherein the digital map data includes a plurality of links connected by nodes representing a navigable path of a network. The departure node, the destination node, and the first location may thus each include a corresponding link or node located within the network. The boundaries and areas surrounding the nodes may thus similarly include a number of links or nodes located within the network.

[0037] As described herein, the boundaries around a given node associated with a particular value of a parameter that constrains the traversable distance can generally be determined using any suitable method for determining the distance that can be traveled from (or to) a node based on the particular value of the parameter. For example, in embodiments, it is contemplated that the boundaries can be determined based on the respective values ​​of the parameters and a route planning algorithm that takes into account the route planning preferences of the navigation device or devices associated with a person or vehicle. The route planning algorithm may, for example, take into account a route planning function (e.g., length, travel time, and / or travel speed) associated with each of a plurality of links defining a route extending around a particular node in order to preferentially select the shortest, fastest, or most fuel- or energy-efficient route between the node and any particular location (assuming the parameter has a first value) from which a person or vehicle can travel to the node. Generally speaking, the algorithm will use a one-to-many search algorithm to explore the links around the destination node. For any given route between a destination node and a location, each of the links along the route is assigned a specific value or cost in terms of the parameter and, optionally, the routing function, such that the route has a cumulative value or cost in terms of the parameter and, optionally, the routing function. The boundary associated with a particular value of the parameter can thus be determined by the endpoints of the route whose cumulative cost or value of the parameter matches that value. Typically, the algorithm used to determine the reachable area or boundary can explore links closer to the destination node in more detail than links further away.

[0038] The first boundary and / or boundaries may be determined as a first step of the method, or they may be predetermined (with data indicative of the boundaries being retrieved (e.g., from persistent memory of a device implementing the method, or from an external server)) and then used in a subsequent comparison step. It will be appreciated that, because a destination node is typically a fixed point, the reachable area around the destination node tends not to change significantly over time, such that the determined reachable area or boundaries around the destination node can be reused or at least re-determined with relatively little computational overhead for multiple different instances of travel through a map area.

[0039] The destination node is typically a fixed location on a map (e.g., corresponding to a home location, or some other predetermined location). For example, in the case where the parameter is the fuel load of a vehicle or the charge level of an electric vehicle, the destination node may include a specific refueling or recharging point. It will be appreciated that because the location of the destination node is typically fixed, the reachability boundary around the destination node can be expected to remain relatively constant over time.

[0040] It is also contemplated that there may be multiple fixed destination nodes, and the method may determine a safe return distance to any or all of these fixed destination nodes. For example, the method may change the destination node used in real time upon moving out of the safe return distance from one destination node but into the safe return distance from another destination node. Alternatively, the safe return distances associated with different destination nodes may be visualized together on a map using, for example, different colors.

[0041] The first location is generally a location within the current reachable area relative to the departure node. The first location is also within the reachable area around the destination node (i.e., the first area within the first boundary). For other locations within the current reachable area relative to the departure node that are not within the reachable area or boundary of the destination node, it will be impossible to safely return to the destination node, and therefore these locations will always be outside the safe return range.

[0042] The method may generally be a method for determining, for a mobile navigation device or a vehicle in which the mobile navigation device is installed, an area within which travel is possible when traveling between a departure node and a destination node. The device may be, for example, a portable navigation device (PND) of the type described in the background section above.

[0043] It will be appreciated that, for example, the value of a parameter at a first location is only an estimate of the expected value of the parameter at the first location, and that changes in traffic conditions, for example, may result in deviations from the estimated value. Thus, the method can be viewed as a method for approximately determining the area within which travel is possible when traveling between a departure node and a destination node, assuming that the parameter constraining the distance travelable by a person or vehicle has an initial value.

[0044] In an embodiment, the method comprises determining or retrieving data indicating a plurality of different boundaries around a destination node, each different boundary being associated with a different respective value of the parameter, the different boundaries enclosing an area around the destination node, the area representing a location from which a person or vehicle could travel to the destination node assuming the parameter associated with the boundary has the value.

[0045] The method further includes: determining which two adjacent boundaries of the boundaries the first location is located between; and comparing the estimated value of the parameter at the first location with the value of the parameter associated with the outer boundary and / or the inner boundary of the two boundaries to determine whether the person or vehicle can reach the first location from the departure node while still reaching the destination node assuming that the parameter has the initial value.

[0046] Typically, the comparison is made between the estimated value of the parameter at the first location and the value of the parameter associated with the outer boundary of the two boundaries between which the first location is located. Thus, the inner boundary is effectively used only to identify which outer boundary to use in the comparison. However, it will be appreciated that the comparison may also or additionally be based on the value of the parameter associated with the inner boundary of the two boundaries between which the first location is located. The outer boundary is the boundary farthest from the destination node.

[0047] Each boundary may be associated with an increasing value of a parameter, such that each boundary represents an increasing distance that can be traveled from the destination node. For example, the boundaries may be arranged concentrically around the destination node. However, it will be appreciated that, depending on how the parameter is defined, each boundary may be associated with a decreasing value of the parameter, such that each boundary represents an increasing distance that can be traveled from the destination node.

[0048] Multiple boundaries generally represent a series of increasing traversable distances to the destination node, such that adjacent boundaries define a series of annular areas around the destination node. The method may therefore include determining in which of the annular areas a particular location is located, and comparing the expected value of the parameter at the location with the value of the parameter associated with the annular area. The adjacent annular areas may be associated with a range of traversable distances corresponding to adjacent ranges or values ​​of the parameter. That is, each annular area represents the additional traversable distance associated with changing the value of the parameter. For example, an annular area defined between an inner boundary associated with a first value of the parameter and an outer boundary associated with a second value of the parameter represents an additional traversable distance associated with changing the value of the parameter from a value less than (or equal to) the first value to a value between the first value and the second value.

[0049] In an embodiment, the method further comprises:

[0050] estimating a value of the parameter when the person or vehicle is at a second location within the first boundary and / or between adjacent two boundaries of the plurality of boundaries instead of the departure node and the destination node and the first location based on the initial value of the parameter at the departure node and an estimated change in the value of the parameter associated with traveling from the departure node to the second location within the first boundary; and

[0051] The estimated value of the parameter at the second location is compared with the first value and / or the value of the parameter associated with the outer boundary and / or the inner boundary of the two boundaries to determine whether the person or vehicle can reach the second location from the departure node while still reaching the destination node assuming that the parameter has the initial value.

[0052] The second location may be within a first area enclosed by a first boundary, or may be within a different area defined between two adjacent boundaries of the plurality of boundaries. The method may therefore include comparing the estimated value of the parameter at the second location with the value of the parameter associated with the area within which the second location is located to determine whether the person or vehicle can reach the second location from the departure node while still reaching the destination node, assuming the parameter has the initial value.

[0053] The method may include: estimating the value of the parameter when the person or vehicle is located at the third or other location (rather than the departure node and the destination node and the first location and the second location) and / or between two adjacent boundaries of the multiple boundaries based on the initial value of the parameter at the departure node and the estimated change in the value of the parameter associated with traveling from the departure node to a third or other location within the first boundary; and comparing the estimated value of the parameter at the third or other location with the value of the parameter associated with the first boundary and / or the outer boundary and / or the inner boundary of the two boundaries to determine whether the person or vehicle can reach the third or other location from the departure node while still reaching the destination node assuming that the parameter has the initial value.

[0054] The method may include performing, at each of a plurality of locations, the steps described above of estimating a value of the parameter and comparing the estimated values ​​of the parameter.

[0055] The method generally involves determining whether a person or vehicle can reach a first location and a second location, or a first location, a second location, a third location, and other locations, from the same departure node (i.e., when the departure node is at a single fixed location). This can then be repeated for the first location (or different locations), the second location, the third location, and / or other locations for different departure nodes (e.g., when the departure node moves or is updated), as discussed in more detail below.

[0056] In an embodiment, the method comprises determining an area around the departure node, the area representing locations to which the person or vehicle may travel from the departure node based on the initial value of the parameter; and

[0057] For each of a plurality of locations within the area around the departure node, the first boundary and / or at least some of the plurality of different boundaries are used to determine whether each of the plurality of locations can be reached while still reaching the destination node.

[0058] The area around the departure node, which represents a location to which the person or vehicle can travel from the departure node based on the initial value of the parameter, can be determined using any suitable method, such as that used to determine a currently reachable area around the departure node. For example, the currently reachable area based on the initial value of the parameter can be determined using the same method used to determine one or more boundaries around a destination node.

[0059] For each of a plurality of locations, it may first be determined whether the location is within a reachable area or boundary of the destination node.

[0060] If a particular location is outside the furthest reachable region of the destination node (i.e., outside the bounds associated with the maximum (or minimum) value of the parameter), then that location can never be reached from the departure node while still being reachable. Locations that fall outside the furthest reachable region of the destination node can be ignored, or can be included in the analysis but compared, for example, to a virtually infinite value of the parameter, such that the location is always determined to be unreachable assuming the current value of the parameter.

[0061] However, for locations that do fall within the reachable area or boundaries of the destination node (i.e., fall within the first boundary and / or one or more of the multiple boundaries), the method may continue as above so that the value of the parameter at the location can be compared with the value of the parameter associated with the area around the destination node (within which the location falls) in order to determine whether it is still possible to reach the destination node.

[0062] It will be appreciated that the area around the departure node, representing the locations to which the person or vehicle can travel from the departure node based on the initial values ​​of the parameters, essentially represents the currently reachable area relative to the departure node. Thus, embodiments allow direct calculation of the safe return distance to the destination node based on the determination of the currently reachable area without significantly increasing the computational workload.

[0063] Live location data (e.g., live GPS data) reflecting current or recent traffic conditions within an area of ​​a map containing the departure node and the destination node can be used to determine an area around the departure node representing locations to which the person or vehicle can travel from the departure node based on the initial value of the parameter.

[0064] In an embodiment, the method further includes using the method to optionally create map data of an area in real time and / or display the area, wherein the area includes locations between the departure node and the destination node that can be reached from the departure node while still being able to reach the destination node based on the initial value of the parameter.

[0065] The created map data can, for example, be maintained for subsequent display to the user (e.g., when the user selects the information for display). By displaying an area between the departure node and the destination node that can be reached from the departure node while still reaching the destination node based on the initial values ​​of the parameters, the user is provided with a visual approximation of the area that can be reached while still reaching the destination node, thereby helping to reduce the driver's range anxiety. The area can be visualized and displayed in any suitable manner. Generally speaking, the area will be defined by a plurality of discrete points, with at least some of these points interconnected to form the area.

[0066] The departure point and the initial values ​​of the parameters may change over time, in which case the method may be continuously executed so that the safe return distance is constantly re-determined. The area to be displayed may thus change in real time as the departure point and / or the initial values ​​of the parameters change.

[0067] In an embodiment, the method comprises creating map data of the or an area around the departure node and / or displaying the area, the area representing the distance the person or vehicle can travel from the departure node based on the initial value of the parameter.

[0068] The distance may correspond to the currently accessible area around the departure node. Optionally, map data for the distance or the distance may be displayed in real time. The currently accessible area relative to the departure node and the safe return area to the destination node may be displayed simultaneously or may be displayed simultaneously.

[0069] In an embodiment, the departure node is the current location of the person or vehicle, and the initial value is the current value of the parameter.

[0070] The method may then include repeating in real time as the current position and the current value of the parameter change: estimating the value of the parameter at the first position and comparing the estimated value of the parameter at the first position with the first value.

[0071] The current location of the person or vehicle may be determined based on live location data (eg, provided by GPS), which is continuously or periodically updated as the person or vehicle moves within the vicinity of the map area.

[0072] The steps of estimating the value of the parameter and comparing the estimated value of the parameter may be repeated at the or a second or other location, wherein the estimated value of the parameter at the second or other location is compared with the value of the parameter associated with the area or boundary within which the second or other location is located.

[0073] In embodiments, (i) the parameter may be a fuel load or a charge level; and / or (ii) the parameter may represent a travel time or a travel distance; and / or (iii) the first value of the parameter is the travel time or distance from the first boundary to the destination node, the initial value of the parameter is the desired or maximum travel time or distance, and the estimated value of the parameter at the first position is the estimated remaining travel time or distance after traveling from the departure node to the first position.

[0074] For example, if the parameter is travel time, the constraint may be a desired maximum travel time or a desired arrival time at the destination node. Similarly, if the parameter is travel distance, the constraint may be a desired maximum travel distance. If the parameter is fuel load or charge level, the constraint may be the initial or current value of the fuel load or charge level.

[0075] The value of the parameter may substantially decrease over time without increasing (or increase without decreasing) as a person or vehicle moves from a departure node to a destination node. The method may determine whether a person or vehicle can reach a specific location from the departure node while still reaching the destination node without requiring the vehicle to refuel or recharge, for example, at a dedicated refueling or recharging point.

[0076] The destination node is a fixed location and / or one or more boundaries around the destination node are determined using or retrieved from stored or historical data.

[0077] The destination node may be a fixed location on the map, such that the first boundary and / or boundaries around the destination node are not expected to change significantly over time. Thus, the boundaries may be determined using or retrieved from stored or historical data, and this may still provide a good approximation of the safe return distance. The stored or historical data may be reused or used multiple times over an extended period of time (e.g., corresponding to multiple different executions of the method or multiple different trips within a map area).

[0078] The location of the destination node and the boundaries around the destination node may be semi-permanently stored, for example, in persistent memory of the mobile device, such that this data is retained for subsequent use even after the method is completed and / or the mobile device is turned off.

[0079] From another aspect, there is provided a mobile device, optionally a portable navigation device, for navigating between a departure node and a destination node, comprising:

[0080] memory; and

[0081] A processor, wherein the processor is configured to:

[0082] determining or retrieving data indicating a first boundary enclosing a first area around the destination node, the first area representing a location from which a person or vehicle carrying the device may travel to the destination node assuming a parameter has a first value, wherein the value of the parameter constrains a distance that may be traveled by the person or vehicle carrying the device;

[0083] estimating a value of the parameter when the person or vehicle carrying the device is at the first location other than the departure node and the destination node based on the initial value of the parameter at the departure node and an estimated change in value of the parameter associated with traveling from the departure node to a first location within the first boundary; and

[0084] The estimated value of the parameter at the first location is compared to the first value to determine whether the person or vehicle carrying the device can reach the first location from the departure node while still reaching the destination node, assuming the parameter has the initial value.

[0085] From another aspect, a system for navigating between a departure node and a destination node is provided, comprising:

[0086] A mobile device having a memory and a processor; and

[0087] a server, wherein the mobile device is configured to communicate with the server;

[0088] wherein the server and / or the processor are arranged and configured to:

[0089] determining or retrieving data indicating a first boundary enclosing a first area around the destination node, the first area representing a location from which a person or vehicle carrying the device may travel to the destination node assuming a parameter has a first value, wherein the value of the parameter constrains a distance that may be traveled by the person or vehicle carrying the device;

[0090] estimating a value of the parameter when the person or vehicle carrying the device is at the first location other than the departure node and the destination node based on the initial value of the parameter at the departure node and an estimated change in value of the parameter associated with traveling from the departure node to a first location within the first boundary; and

[0091] The estimated value of the parameter at the first location is compared to the first value to determine whether the person or vehicle carrying the device can reach the first location from the departure node while still reaching the destination node, assuming the parameter has the initial value.

[0092] The mobile device may, for example, be a user's smartphone or smartwatch running appropriate software. Alternatively, the mobile device may be a dedicated portable navigation device, for example, having any of the features described above in the background section. Generally, the mobile device will have GPS functionality and access live data related to the area surrounding the mobile device. This live data may be transmitted to the mobile device from an external server via a wireless connection. Typically, the mobile device will have a display so that the safe return distance can be visualized or displayed to the user.

[0093] The processor may be arranged and configured to provide the functionality stated above, wherein the server merely provides information or data for use by the processor in performing these steps. For example, the server may provide live data representing current map conditions that can be used to estimate the value of the parameter. In other embodiments, some or all of the stated functionality may be provided at the server, with the results or data indicative of the results then being passed to the mobile device, for example, for subsequent use by the processor and / or subsequent display to the user. It is also contemplated that the server and processor may be arranged and configured to cooperate in order to provide the stated functionality.

[0094] The processor and / or server may also or additionally be arranged and configured to perform any or all of the method steps described above with respect to the first aspect, at least insofar as they are not mutually exclusive. Again, these steps may be performed directly by the processor of the mobile device, or alternatively, the method steps may be performed by the server, with the results or data indicative of the results then being passed to the mobile device (e.g., for subsequent display to a user).

[0095] In an embodiment, data indicative of a first boundary of a first area enclosing the destination node may be stored in a persistent memory portion of the memory.

[0096] In other embodiments, data indicative of a first boundary enclosing a first area around the destination node is retrieved from the server or from an external server.

[0097] It will be appreciated that using multiple boundaries around the destination node, data indicative of each of the multiple boundaries may be stored in a persistent memory portion of memory or may be retrieved from the server or from an external server.

[0098] From another aspect, there is provided a computer-implemented method for determining an area within which one may travel when travelling between a departure node and a destination node, comprising a method substantially as described above.

[0099] From a further aspect, there is provided a computer program product comprising computer readable instructions which, when executed by a computer, cause the computer to perform a method substantially as described above.

[0100] Aspects and embodiments of the invention as set out above may be described additionally or alternatively as follows.

[0101] According to another aspect of the present invention, there is provided a method of determining a first boundary enclosing a portion of a geographic area containing a navigable network, the portion representing an area reachable from a first location on the navigable network while still allowing a second location on the navigable network to be reached, assuming a parameter limiting the amount of the navigable network that can be traversed has a value, the navigable network being represented by an electronic map, the electronic map including a plurality of road segments representing navigable elements of the navigable network, the method comprising:

[0102] determining a position on a road segment representing the first position and obtaining the value of the parameter at the determined position;

[0103] exploring road segments of the electronic map relative to the determined location representing the first location using a search algorithm having an associated cost function, and for road segments explored and determined to be reachable, wherein the road segment is reachable if it is associated with a value of the parameter resulting from traversing a best-cost route from the determined location representing the first location that is less than the obtained value of the parameter; determining whether the road segment is within a second boundary, the second boundary being associated with a value of the parameter that is greater than a difference between the obtained value of the parameter and the value of the parameter associated with the road segment, wherein the second boundary is one of a plurality of predetermined second boundaries, each predetermined second boundary being associated with a different value of the parameter, and each predetermined second boundary enclosing a portion of the geographic area around the second location, the portion representing an area from which the second location is reachable assuming the parameter has an associated value; and

[0104] The first boundary is determined using the road segments determined to be within the second boundary.

[0105] The present invention provides a method for determining a so-called "safe return range" (i.e., the portion of a navigable network that can be reached from a first location (e.g., a current location) while still allowing a second location (e.g., a predetermined 'home' location) to be reached, assuming a parameter that limits the amount of the navigable network that can be traversed has a value). As will be discussed in more detail below, the parameter may be the fuel load or energy level of the vehicle, or in other embodiments, the parameter may be the maximum time or distance that can be spent in a trip, and thus the value of the parameter associated with the first location (e.g., the current location) may reflect the current fuel load or energy level of the vehicle (i.e., a value between zero (i.e., empty) and a maximum value (i.e., full)) or reflect the remaining distance or time that can be traveled.

[0106] The invention extends to a system for performing a method according to any of the aspects or embodiments of the invention described herein.

[0107] Thus, according to another aspect of the present invention, there is provided a method for determining a first boundary enclosing a portion of a geographic area containing a navigable network, the portion representing an area reachable from a first location on the navigable network while still allowing a second location on the navigable network to be reached, assuming a parameter limiting the amount of the navigable network that can be traversed has a value, the navigable network being represented by an electronic map, the electronic map including a plurality of road segments representing navigable elements of the navigable network, the system comprising:

[0108] means for determining a position on a road segment representing said first position and obtaining said value of said parameter at said determined position;

[0109] means for: exploring, using a search algorithm having an associated cost function, road segments of the electronic map relative to the determined location representing the first location, and for road segments explored and determined to be reachable, wherein the road segment is reachable if it is associated with a value of the parameter resulting from traversing a best-cost route from the determined location representing the first location that is less than the obtained value of the parameter; determining whether the road segment is within a second boundary, the second boundary being associated with a value of the parameter that is greater than a difference between the obtained value of the parameter and the value of the parameter associated with the road segment, wherein the second boundary is one of a plurality of predetermined second boundaries, each predetermined second boundary being associated with a different value of the parameter, and each predetermined second boundary enclosing a portion of the geographic area around the second location, the portion representing an area from which the second location is reachable assuming the parameter has an associated value; and

[0110] Means for determining the first boundary using the road segments determined to be within the second boundary.

[0111] As will be appreciated by those skilled in the art, this other aspect of the invention may, and preferably does, include any one or more or all of the preferred and optional features of the invention described herein with respect to any of the other aspects of the invention, as appropriate. Where not explicitly stated, the system of the invention herein may include means for performing any of the steps described with respect to the method of the invention in any of its various aspects or embodiments, and vice versa. The invention is a computer-implemented invention, and any of the steps described with respect to any of the various aspects or embodiments of the invention may be performed under the control of a set of one or more processors. The means for performing any of the steps described with respect to the system may be a set of one or more processors.

[0112] The system of the present invention in any of its aspects or embodiments may be in the form of any suitable device, such as a navigation device. Generally speaking, the system of the present invention may be at least one processing device. The or a processing device may be a mobile device (such as a navigation device, whether a portable navigation device (PND) or an integrated device) or a server.

[0113] In a preferred embodiment, the method of the invention in any of its aspects or embodiments is performed using a mobile device (e.g. a navigation device), and the invention extends to a mobile (e.g. a navigation) device arranged to perform the steps of the method of any of its aspects or embodiments. The navigation device may be a portable navigation device (PND) or an integrated (e.g. in-vehicle) device.

[0114] According to any of the aspects or embodiments of the present invention, the system (e.g., a navigation device) may include a display for displaying an electronic map together with at least a representation of the determined first boundary to a user, a set of one or more processors configured to access electronic map data and cause the electronic map to be displayed to the user via the display, and a user interface operable by the user to enable the user to interact with the device.

[0115] Regardless of its implementation, the device (e.g., navigation device) used in any one of its various aspects or embodiments according to the present invention may include a processor, a memory, and digital map data (or electronic map) stored in the memory. The processor and memory cooperate to provide an execution environment in which a software operating system can be established. One or more additional software programs may be provided to enable control of the functionality of the device and to provide various other functions. The device (e.g., navigation device) may preferably include a global navigation satellite system (GNSS) (e.g., GPS or GLONASS), signal reception and processing functionality. As will be appreciated, the device may optionally use other components for determining its current location, such as ground beacons, mobile telecommunications networks, etc. The device may include one or more output interfaces that can relay information to the user via the one or more output interfaces. In addition to a visual display, the output interface may also include a speaker for audible output. The device may include an input interface that includes one or more physical buttons to control the on / off operation or other features of the device.

[0116] In other embodiments, the method of the present invention in any of its aspects or embodiments may be performed by a server, and the present invention extends to a server that is arranged to perform the steps of the method of any of its aspects or embodiments. The system of any of its aspects or embodiments may be a system of processing devices such as a server. Of course, the steps of the method of the present invention in any of its aspects or embodiments may be performed in part by a server and in part by a navigation device. For example, the first boundary may be determined by the server (e.g., at the request of a navigation device) and provided to the device for output to the user. The steps of the method may be performed exclusively on the server, or some steps may be performed on the server and other steps may be performed on the navigation device in any combination, or may be performed exclusively on the navigation device. Executing one or more of the steps on the server may be efficient and may reduce the computational burden placed on the navigation device. Alternatively, if one or more steps are performed on the navigation device, this may reduce any bandwidth required for network communication. Therefore, the system of the present invention may be provided in part by a navigation device or other mobile device, and in part by a server.

[0117] Navigable networks are represented by electronic maps. These electronic maps consist of multiple road segments connected by nodes. In their simplest form, these electronic maps (or mathematical graphs, as they are sometimes called) are essentially databases containing data representing nodes, most commonly road intersections, with lines between those nodes representing roads between those intersections. In more detailed digital maps, lines can be divided into road segments defined by start and end nodes. These nodes can be "real," representing road intersections where at least three lines or road segments intersect, or they can be "artificial," providing anchor points for road segments not bounded by real nodes at one or both ends to provide, among other things, shape information for a particular road segment, or to identify locations along a road where some characteristic of the road (e.g., speed limit) changes. These nodes and road segments are further defined by various attributes, again represented by data in the database. For example, each node will typically have geographic coordinates defining its real-world location (e.g., latitude and longitude). Nodes will also typically have associated with them maneuvering data indicating whether it is possible to move from one road to another at an intersection; while the road segments will also have associated attributes, such as legal speed limits, etc. The road segments also have associated traversal directions indicating the possible directions along which the road segment can travel. For example, when the navigable network is a road network, the road segment may represent a one-way road, or the road segment may represent a lane on one side of a highway, and thus the road segment will be unidirectional (i.e., allowing travel from one node to another, but not in the other direction). Alternatively, and as is generally more common, the road segment may be bidirectional (i.e., allowing travel from one node to another, and vice versa). A bidirectional road segment may therefore always be an outbound road segment relative to the area of ​​the soft position, but this is not the case for a unidirectional road segment.

[0118] Although embodiments of the present invention are described with reference to road segments, it will be appreciated that the present invention is also applicable to other navigable segments, such as segments of paths, rivers, waterways, cycle paths, towpaths, railway lines, etc. For ease of reference, these segments are collectively referred to as road segments, but any reference to a "road segment" may be replaced by a reference to a "navigable segment" or any one or more specific types of such segments.

[0119] In the present invention, data representing a first location is obtained. The first location is preferably the current location of a user or mobile device, but the first location can be any location from which the user desires to begin a journey. Therefore, in the case where the first location is the current location of a mobile device (e.g., a GNSS receiver), data representing the first location can be obtained from the location determination means of the mobile device. Alternatively, (for example) in the case where a user provides an address or marks a location on an electronic map, the data representing the first location can be based on information received from the user. The data representing the first location is used to determine a location on a road segment of the electronic map corresponding to the first location. The location on the road segment can be a location along the road segment, or can be one or other of the nodes defining the road segment. The value of a parameter at the location on the road segment (i.e., the first location) is also obtained. (For example) when a device is operatively connected to a vehicle via a wired or wireless connection, the value of the parameter can be received from the vehicle. For example, this can be a situation where the parameter reflects the current fuel or energy level of the vehicle. Alternatively, the value of the parameter may be received from the user, for example, where the user provides the value using suitable input means of the device. For example, this may be the case where the parameter reflects the remaining (or maximum) time or distance to be traveled. As will be appreciated, the value of the parameter obtained automatically or based on received user input will preferably be a value between zero (e.g., indicating an empty fuel tank) and a maximum value (e.g., indicating a full fuel tank). It will also be appreciated that the value of the parameter may be based on received information (e.g., from the vehicle or the user), such that the value of the parameter used in the method may not directly match the received value.

[0120] In the present invention, a search (or routing) algorithm with an associated cost function is used to explore road segments of the electronic map relative to the determined location. The search algorithm preferably comprises an undirected search and thus operates to identify an optimal path or route (e.g., typically a lowest-cost path) through the electronic map (and thus through the navigable network) from the determined location representing the first location. The search (or routing) algorithm is therefore preferably a "forward" search, since the intended direction of travel is outward from the first location. The search is undirected, since there is no predetermined destination or target. In other words, the search algorithm can be considered a one-to-many algorithm and thus operates to identify optimal paths or routes from the determined location representing the first location to multiple nodes of the electronic map. As will be appreciated, a one-to-many routing algorithm differs from a one-to-one routing algorithm in that the one-to-one routing algorithm is designed to determine the optimal path between two locations in the electronic map. The routing algorithm of the present invention may take any suitable form as desired, such as one based on Dijkstra's algorithm or the like. The optimal (or lowest cost) routes referred to herein and determined by the route planning algorithm are optimized with reference to an associated cost function. The cost function may be predetermined or user-selectable and may be intended to identify a route between two locations that has, for example, the shortest distance between the two locations, the fastest travel time between the two locations, the lowest fuel consumption between the two locations, or any combination thereof as desired. The cost of a route may be determined as the sum of the costs of traversing at least one road segment forming the route, wherein the cost for traversing each road segment is determined using the cost function and at least one attribute typically associated with the respective road segment (e.g., the length of the road segment, the expected travel speed along the road segment, the elevation change along the road segment, the curvature (or shape) of the road segment, etc.).

[0121] The exploration step includes determining whether a segment explored by the route planning algorithm can be reached from the location representing the first location, assuming that the parameter at the first location has the obtained value. As discussed above, if a segment is associated with a value of the parameter that is smaller than the obtained value of the parameter resulting from traversing the optimal (e.g., lowest) cost route from the location representing the first location, then the segment is determined to be reachable. In other words, for each segment explored, there is a determined path comprising one or more segments relative to the location representing the first location that is optimal (e.g., the lowest cost route) in terms of cost. As will be appreciated, each of the one or more segments forming a path to a particular segment produces a value for the parameter associated with traversing the network from the first location to the navigable element represented by the segment in question in the navigable network. In other words, traversing the navigable network requires, for example, consuming a specific amount of time, distance, or fuel. Therefore, for example, the cost function associated with the route planning algorithm is used to determine the first cost for crossing a road segment, and the objective function is used to determine the second cost for crossing the road segment, (for example) wherein the second cost is one of time, distance, fuel or energy. The optimal path leading to the road segment is (for example) the path with the lowest cumulative first cost. In such embodiments, the parameter associated with the explored road segment is the cumulative second cost of one or more road segments forming the optimal path from the position associated with the first position to the road segment, for example, the time required for crossing the path, the distance of the path, the fuel required for crossing the path, etc. Therefore, it will be understood that the search algorithm preferably includes a non-directional forward search, and when the parameter exceeds the obtained value on all explored paths, the non-directional forward search stops.

[0122] Because the present invention includes determining whether the explored road segment is reachable, the method of determining a first boundary representing a safe return route may also include determining a third boundary enclosing a portion of the navigable network in the geographic area, the portion representing a reachable area relative to the first location assuming the parameter at the first location has the obtained value. In practice, it is preferred that the first boundary and the third boundary be determined in the method of the present invention so that representations of both boundaries can be displayed to the user (e.g., simultaneously).

[0123] As discussed above, the first boundary and / or the third boundary enclose a portion of the geographic area. The boundaries can be defined in any suitable and desired manner. For example, the boundaries can be defined by multiple discrete locations (e.g., multiple nodes of an electronic map), wherein the boundaries are defined by interconnecting these locations. For example, in the case of the first boundary, the node farthest from the first location along the segment of each of the explored paths can be used as the multiple discrete locations. For example, and as described in WO 2014 / 001565 A1 (the entire contents of which are incorporated herein by reference), the portion of the geographic area around the first location can be divided into multiple sectors (e.g., 16 sectors), and for each sector, the farthest point (e.g., node) of the determined boundary from the first location is stored. The discrete locations (e.g., nodes) are preferably connected by lines (e.g., arcs) to form a continuous boundary.

[0124] In the present invention, for each road segment that has been explored and deemed reachable, the method includes determining whether the road segment is located within a second boundary, the second boundary being associated with a value of the parameter that is greater than the value of the parameter associated with the corresponding road segment. The second location is preferably a location selected by the user, and is preferably a location that represents a location commonly used by the user. For example, the second location may be a 'home' location, and thus the safe return distance is an area that can be reached from the first location (e.g., the current location) on the navigable network while still allowing the user to reach the home. However, it will be understood that the second location may be any predetermined location, such as the user's 'work' location or the residence of a family member.

[0125] The second boundary is one of a plurality of predetermined second boundaries, each of the plurality of predetermined second boundaries being associated with a different value of the parameter. Each second boundary encloses a portion of a geographic area around the second location representing an area from which the second location can be reached, such that the plurality of second boundaries effectively form a series of rings or layers around the second location. Data indicating the plurality of second boundaries is preferably stored in a memory of the device. The data is preferably stored in non-volatile memory, for example, such that the data is retained in the memory upon powering off and on the device. The method preferably includes determining the plurality of second boundaries.

[0126] Determining the second boundary for the value of the parameter preferably includes: determining a position on a road segment representing the second location; and exploring the road segment of the electronic map relative to the determined position representing the second location using a search (or route planning) algorithm with an associated cost function. The search algorithm preferably comprises an undirected search and thus operates to identify an optimal path or route (e.g., typically a lowest-cost path) through the electronic map (and thus through the navigable network) that ends at the determined position representing the second location. The search (or route planning) algorithm is therefore preferably a "backward" search because the intended direction of travel is toward the second location. The search is undirected because there is no predetermined destination or target. In other words, the search algorithm can be considered a one-to-many algorithm and thus operates to identify optimal paths or routes from multiple nodes of the electronic map to the determined position representing the second location. The route planning algorithm of the present invention may take any suitable form as desired, such as one based on the Dijkstra algorithm or the like. As discussed above, the optimal (or lowest-cost) route referred to herein and determined by the route planning algorithm is optimized with reference to the associated cost function. The cost function may be predetermined or user-selectable, and may be intended to identify a route between two locations that has, for example, the shortest distance between the two locations, the fastest travel time between the two locations, the lowest fuel consumption between the two locations, or any combination thereof as desired. The cost of a route may be determined as the sum of the costs of traversing at least one road segment forming the route, wherein the cost for traversing each road segment is determined using a cost function and at least one attribute typically associated with the respective road segment (e.g., the length of the road segment, the expected travel speed along the road segment, the elevation change along the road segment, the curvature (or shape) of the road segment, etc.). In a preferred embodiment, the same cost function is associated with (and used in conjunction with) the search (or route planning) algorithm used to determine the first boundary and, optionally, the third boundary, and is also associated with (and used in conjunction with) the search (or route planning) algorithm used to determine the plurality of second boundaries.

[0127] The exploration step of the method for determining the plurality of second boundaries comprises determining whether a location representing the second location can be reached from a road segment assuming that the parameter has a predetermined value. If the value of the parameter resulting from traversing the optimal (e.g., lowest) cost route from the road segment is less than the predetermined value of the parameter, then the second location is determined to be reachable from the road segment. Conversely, if the value of the parameter resulting from traversing the optimal (e.g., lowest) cost route from the road segment is greater than the predetermined value of the parameter, then the second location is determined to be unreachable. In other words, for each road segment explored, there is a determined path comprising one or more road segments from the road segment to the location representing the second location that is optimal (e.g., the lowest cost route) in terms of cost. As will be appreciated, each of the one or more road segments forming the location representing the second location is associated with a value of the parameter, for example, because traversing the navigable network requires, for example, consuming a certain amount of time, distance, or fuel. Therefore, for example, the cost function associated with the route planning algorithm is used to determine the first cost for crossing the road segment, and the objective function is used to determine the second cost for crossing the road segment, (for example) wherein the second cost is one of time, distance, fuel or energy. The optimal path leading to the road segment is (for example) the path with the lowest cumulative first cost. In such embodiments, the parameter associated with the explored road segment is the cumulative second cost of one or more road segments forming the optimal path from the road segment to the location associated with the second location, for example, the time required for crossing the path, the distance of the path, the fuel required for crossing the path, etc. Therefore, it will be understood that the search algorithm preferably includes an undirected backward search, and when the parameter reaches a maximum value (for example, full) on all explored paths, the undirected backward search stops, because the parameter is considered to be zero (for example, empty) at the second location. The reachability mileage defined by the complete search preferably forms the outermost second boundary, and the other second boundaries are at intermediate parameter values ​​between zero and the maximum value.

[0128] Each of the second boundaries is associated with a different value of the parameter, such that the second boundaries effectively form a series of layers or rings around the second location. For example, in an embodiment where the parameter represents the fuel load or energy level of the vehicle, the outermost second boundary (i.e., the second boundary enclosing the largest portion of the geographic area) represents the portion of the navigable network from which the second location can be reached assuming the maximum amount of fuel or energy. The remaining second boundaries represent progressively smaller portions of the geographic area because they are associated with less than the maximum amount of fuel or energy for the vehicle. For example, boundaries can be determined for fuel or energy levels of the vehicle that are 10%, 20%, 30%, ..., up to 100% full. However, it will be understood that any number of boundaries can be determined as desired, such as for example, for distance intervals of 5 km or 10 km from the second location to the maximum reachable distance (i.e., fuel or energy levels equivalent to such distance ranges). In embodiments where the parameter indicates a time or distance that may be taken for a trip (i.e., where the obtained value of the parameter is a maximum time or distance, and where the obtained value is a value selected from a predetermined range), the plurality of second boundaries may be determined for selected time or distance intervals within the predetermined range.

[0129] In an embodiment, the plurality of second boundaries may be recalculated whenever a predetermined triggering event occurs. The triggering event may be one or more of the following: a change in the second location; a change in the electronic map; a change in the selected cost function to be used in the route planning algorithm; when the mobile device (on which the method is executed) is restarted (i.e., turned 'on' from an 'off' state); and when the software application (performing the method) is opened (i.e., executed by a software launcher application). As will be appreciated, by triggering the recalculation of the plurality of second boundaries each time the mobile device and / or software application is launched, this allows the plurality of second boundaries to be kept relatively up to date with current conditions on the navigable network (e.g., road closures, significant traffic congestion events, etc.).

[0130] Those skilled in the art will appreciate that the route planning algorithm used to determine the first boundary and, optionally, the third boundary preferably always takes into account real-time traffic and other travel conditions on the navigable network (when available), however, because the plurality of second boundaries are predetermined and stored, the plurality of second boundaries will not always represent current traffic and travel conditions on the navigable network. The safe return range determined by the method of the present invention will therefore typically be an estimate of the actual range. Thus, in embodiments, the parameters used in the present invention may not correspond to the actual fuel or energy level of the vehicle, but may include a buffer such that, for example, the outermost second boundary may correspond to a 95% fuel or charge level rather than a 100% fuel or charge level.

[0131] Each of the plurality of second boundaries encloses a portion of a geographic area and can be defined in any suitable and desired manner. For example, the boundary can be defined by a plurality of discrete locations (e.g., a plurality of nodes of an electronic map), wherein the boundary is defined by interconnecting these locations. For example, and as described in WO 2014 / 001565 A1, the portion of the geographic area around the second location can be divided into a plurality of sectors (e.g., 16 sectors), and for each sector, the farthest point of the determined boundary from the second location (e.g., a node) is stored. The discrete locations (e.g., nodes) are preferably connected by lines (e.g., arcs) to form a continuous boundary.

[0132] As discussed above, in the present invention, for a road segment that is explored and deemed reachable, the method includes determining whether the road segment is located within a second boundary, the second boundary being associated with a value of the parameter that is greater than the difference between the obtained value of the parameter and the value of the parameter associated with the road segment. Again as discussed above, each second boundary represents a portion of a geographic area, and therefore a portion of a navigable network, from which the second location can be reached, assuming that the parameter associated with the particular second boundary in question has that value. Thus, and as will be appreciated, when exploring a path outward from a location representing the first location, at some point along each path a road segment will be identified that is within an appropriate second boundary and from which the second location can therefore be reached, however the next road segment in the path (away from the first location) does not fall within the second boundary and from which the second location cannot therefore be reached.

[0133] In an embodiment of the present invention, the location of the current segment being explored is compared to the geographic extent of the plurality of second boundaries to identify the outermost boundary within which the segment can be found. The difference between the obtained value of the parameter and the value of the parameter associated with the segment (i.e., the difference value) can then preferably be compared with the parameter associated with the identified boundary. If the difference value is greater than the parameter associated with the boundary, then the segment is within the safe return mileage; otherwise, it can be determined that the segment is outside the safe return mileage. In an embodiment, the nodes between the segment along the path that is within the second boundary and the adjacent (or neighboring) segment along the path that is at least partially outside the second boundary can be used together with the nodes of all other paths to determine the discrete points that define the boundary of the safe return mileage.

[0134] In other embodiments of the present invention, the second boundary is preferably selected from the plurality of second boundaries based on the difference. The selected second boundary is preferably the second boundary associated with the value of the parameter closest to the difference, and more preferably the second boundary associated with the value of the parameter closest to the difference and also smaller than the difference. In other words, the selected second boundary is the outermost second boundary associated with the value of the parameter smaller than the difference for the section in question. Therefore, if the section is located within the geographic area enclosed by the selected second boundary, it is possible to reach the second location by crossing the navigable network, and therefore the section should be used to determine the first boundary. Conversely, if the section is located outside the geographic area enclosed by the selected second boundary, it is impossible to reach the second location by crossing the navigable network, and therefore the section should not be used to determine the first boundary.

[0135] In an embodiment of the present invention, information representing at least some, and preferably all, of a first boundary or an area enclosed by the first boundary is displayed to a user on a display (e.g., associated with a mobile device). Additionally, in an embodiment, information representing at least some, and preferably all, of a third boundary or an area enclosed by the third boundary is displayed to the user on a display (e.g., associated with a mobile device), preferably simultaneously with the information representing the first boundary. As will be appreciated, the plurality of second boundaries are intended to be used to determine the first boundary and are preferably not intended to be displayed to the user. In embodiments in which the method is performed by a mobile device, the first boundary and / or the third boundary, or portions thereof, may then be displayed on a display of the mobile device. Alternatively, in embodiments in which the method is performed by a server, information representing at least some, and preferably all, of the first boundary and / or the third boundary or an area or areas enclosed by the first boundary and / or the third boundary may then be transmitted to the mobile device for display thereon.

[0136] As will be appreciated, and in embodiments where the first position represents the current position of the mobile device, the method is preferably repeated as the position of the mobile device changes, such that the first boundary and optionally the third boundary are continually recalculated and are preferably the most recently calculated boundary or boundaries displayed to the user. The method may be performed at any desired frequency, such as after a specific time period, after a specific distance has been traveled, after a specific amount of fuel or energy has been used, etc.

[0137] In embodiments, it is contemplated that the method may be extended to determine and / or access data indicating a plurality of second boundaries for each of a plurality of second locations. Thus, a safe return distance may be determined for, for example, a user's 'home,' 'work,' 'gym,' etc., as desired. In such embodiments, the method may include, for example, obtaining a selection of one of a plurality of predetermined second locations based on received user input, and performing the method described above with respect to the selected predetermined second location.

[0138] Any of the methods according to the invention may be implemented at least in part using software (e.g., a computer program). The invention therefore also extends to a computer program comprising computer-readable instructions that are executable to perform or cause a navigation device and / or server to perform a method according to any of the aspects or embodiments of the invention.

[0139] Accordingly, the present invention extends to a computer software carrier comprising such software, which, when used to operate a system or device comprising data processing means, causes the device or system, together with the data processing means, to perform the steps of the method of the present invention. This computer software carrier may be a non-transitory physical storage medium (e.g., a ROM chip, CD ROM, or disk), or may be a signal (e.g., an electronic signal via a wire, an optical signal, or a radio signal (e.g., to a satellite), etc.). The present invention provides a machine-readable medium containing instructions which, when read by a machine, cause the machine to operate according to the method of any of the aspects or embodiments of the present invention.

[0140] No matter how its embodiment is, the navigation device used according to the present invention may comprise a processor, a memory and the digital map data stored in the memory. The processor and the memory cooperate to provide an execution environment in which a software operating system can be set up. One or more additional software programs can be provided to enable the functionality of the control device, and various other functions are provided. The navigation device of the present invention may preferably include GPS (global positioning system) signal reception and processing functionality. The device may comprise one or more output interfaces by which information is relayed to the user. Except for the visual display, the output interface may also include a loudspeaker for audible output. The device may comprise an input interface, and the input interface comprises one or more physical buttons to control the on / off operation or other features of the device.

[0141] In other embodiments, the navigation apparatus may be implemented at least in part by means of a processing device whose application does not form part of a specific navigation device. For example, the present invention may be implemented using a suitable computer system arranged to execute navigation software. The system may be a mobile or portable computer system (e.g., a mobile phone or laptop computer) or may be a desktop system.

[0142] Where not expressly stated, it will be understood that the present invention, in any of its aspects, may include any or all of the features described with respect to other aspects or embodiments of the present invention, as long as they are not mutually exclusive. In particular, although various embodiments of operations that may be performed in the method and by the apparatus have been described, it will be understood that any one or more or all of these operations may be performed in any combination in the method and by the apparatus as desired and appropriate.

[0143] Advantages of these embodiments are set out below, and further details and features of each of these embodiments are defined in the accompanying independent technical solutions and further in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0144] Various embodiments will now be described, by way of example only, and with reference to the accompanying drawings, in which:

[0145] Figure 1 is a schematic representation of one embodiment of the present invention;

[0146] Figure 2 is a flow chart illustrating an embodiment of the present invention; and

[0147] Figure 3 is an example of how the reachable area can be visualized to be displayed to the user. DETAILED DESCRIPTION

[0148] Embodiments of the present invention will now be described with particular reference to PNDs. However, it should be borne in mind that the teachings of the present invention are not limited to PNDs, but are instead generally applicable to any type of processing device configured to execute navigation software to provide route planning and navigation functionality. It follows, therefore, that in the context of the present application, a navigation device is intended to include, but not be limited to, any type of route planning and navigation device, whether embodied as a PND, a navigation device built into a vehicle, or a computing resource that actually executes route planning and navigation software, such as a desktop or portable personal computer (PC), a mobile phone, or a portable digital assistant (PDA).

[0149] Embodiments of the present invention allow for determining an approximation of the area that can be reached from a current location (a departure node) while still reaching home or any other predefined location (a destination node), assuming the parameters constraining the reachable distance have current values. This so-called "safe return range" can then be visualized or displayed to the user on a map to help reduce their range anxiety. For example, where the parameter is the vehicle's current fuel load or charge level, a safe return range can be displayed representing the distance between the current location and the home location that can be safely reached without running out of fuel or charge and while still reaching the home location.

[0150] While in the embodiments of the present invention described below, the parameter is the charge level of the electric vehicle, it will be appreciated that the techniques described herein are not limited to this context and may also be applied with any other suitable constraints. For example, the parameter may represent travel time or distance. Naturally, the maximum travel time or distance may be related to the current fuel load or charge level, as a particular fuel load or charge level will provide a particular amount of arrival or travel time. However, it is also contemplated that the constraint may simply be the time by which a home location must be reached, or the distance a user wishes to travel (e.g., by running). It will also be appreciated that a variety of constraining factors or parameters may exist, and the techniques described herein may generally take one or more of these into account.

[0151] In an embodiment of the present invention, the safe return range is calculated in two steps, essentially using the calculation of the current reachable area. First, a series of boundaries is obtained or determined, representing the area from which the home location can be reached for different corresponding predefined values ​​of a parameter (e.g., charge level). For example, the boundaries can be obtained or determined for a series of discretely increasing values ​​of the parameter. Next, the current reachable area around the current location of the vehicle or device is determined based on the current value of the parameter (e.g., current charge level). Since the boundaries of the reachable area around the home location for different values ​​of the parameter have already been obtained or determined in the first step, it is then easy to determine whether any given location within the current reachable area is also within the reachable area of ​​the home location, assuming the current value of the parameter, simply by comparing the estimated value of the parameter at that location with the value of the parameter required to reach the home location from that location (as determined using the boundaries obtained in the first step). Therefore, there is no need to separately calculate both the current reachable range and the safe return range. The determination of whether any given location is within the safe return range of the home location can be made directly based on the calculation of the current reachable area without significantly increasing the computational workload.

[0152] exist Figure 1 This approach is schematically illustrated in for an electric vehicle whose travelable distance is constrained by the level of charge stored in the battery.

[0153] Figure 1 A map data area around a fixed home location 2 is schematically shown, wherein a vehicle has a current location 1. Figure 1, but it will be understood that the region generally contains a network comprising a series of interconnected nodes and links (i.e., roads and intersections) along which vehicles can travel. Thus, vehicles are constrained to travel along specific links, and generally no straight-line path can exist between any two nodes or points within the region. A series of boundaries 21, 22, 23, 24, 25 around the home location 2 are illustrated, with each boundary 21, 22, 23, 24, 25 enclosing an area representing the distance from which the home location 2 can be reached with increasing charge levels. For example, the first boundary 21 may represent a series of points from which the home location 2 can be reached with only 20% of the remaining charge. A second boundary 22 may then represent a range of points from which Home Location 2 can be reached with only 40% of the charge remaining, a third boundary 23 represents a range of points from which Home Location 2 can be reached with 60% of the charge remaining, a fourth boundary 24 represents a range of points from which Home Location 2 can be reached with 80% of the charge remaining, and a fifth boundary 25 represents a range of points from which Home Location 2 can be reached with a fully charged (100%) battery. For points outside of fifth boundary 25 (i.e., that would require more than 100% charge to travel to Home Location 2), Home Location 2 is inaccessible (unless, for example, the battery is recharged), so these points are always outside the safe return range.

[0154] It will be appreciated that each boundary 21, 22, 23, 24, 25 encloses an area representing locations that are potentially reachable using the charge level associated with that boundary. The annular area defined between adjacent boundaries thus defines locations that are reachable using the range of charge levels defined between those two boundaries. For example, relative to the area enclosed by first boundary 21 representing the area reachable using a 20% charge, the annular area defined between first boundary 21 and second boundary 22 represents an additional area reachable using a 40% charge. It will be appreciated that the shape and extent of boundaries 21, 22, 23, 24, 25 are generally determined using map data and a route-finding algorithm (as discussed in more detail below) and are therefore generally arbitrary polygons representing routes through the network between home location 2 and the boundary used to determine the boundary. However, in its simplest implementation, the boundary can simply be approximated as a series of circles around the home location.

[0155] Figure 1Also shown is a current reachable area 3 around the current location 1, which can be determined in real time based on map data (e.g., live map data) and the current charge value. The vehicle's current location 1 can be determined using GPS data. It will be understood that "live" map data refers to information related to current or relatively current conditions in the map area (e.g., including traffic and weather conditions that may affect travel times and / or speeds of links in the network traversing the map area). This live data can be provided to the device via (i.e., downloaded from) an external server as is known in the art and can be updated regularly. Using boundaries 21, 22, 23, 24, and 25, the safe return distance to the home location 2 for any given location 12 within the current reachable area 3 can be easily determined. For example, for a given location 12 within the current reachable area 3, it is straightforward to determine between which two of the boundaries 21, 22, 23, 24, and 25 surrounding the home location the location 12 lies—i.e., in the illustrated scenario, the location 12 lies between the first boundary 21 and the second boundary 22. To determine whether location 12 is within the safe return range to home location 2, it is then necessary to compare the expected remaining charge after traveling from current location 1 (e.g., along route 112) to that location 12 with the charge value associated with the corresponding boundary 22. For example, if the remaining charge level at location 12 is 50%, then it would be possible to reach that location 12 from current location 1 while still reaching home location 2 (e.g., by traveling along route 122, which may be selected as the shortest route between location 12 and home location 2 using a routing algorithm) because location 12 is within the 40% boundary around home location 2. However, if the remaining charge at location 12 is only 20% (or less), then home location 2 would not be reachable because it is located beyond the 20% boundary.

[0156] It will be appreciated that the accuracy of the approximation can, in principle, be increased by using more or more closely spaced boundaries (e.g., corresponding to smaller increments of charge value). However, it will also be appreciated that the boundaries themselves are only approximations, and the expected charge value at any given location is at best an estimate. Because the boundaries are only approximations, it may be desirable to include a certain buffer in the charge level associated with each boundary, so that a boundary 21 identified to the user as a 20% charge level may actually correspond to, for example, an 18% charge level. It may also be desirable to display to the user, for a particular location, the confidence level associated with that location being within the safe return range. For example, a location determined to be only just within the safe return range may be indicated with a different shading or color than a location expected to be completely within the safe return range.

[0157] Figure 2 This is a more detailed diagram of the above Figure 1 Flowchart of the described embodiment. Figure 2 The embodiment related to determining a safe return range to a home location for a PND installed in an electric vehicle will be described again.

[0158] In a first step 101, a "backward" route search relative to the home location is performed to generate a series of boundaries, each associated with an increasing charge level (e.g., a range of kilometers). Thus, each boundary encloses an area that includes locations that are reachable assuming a particular charge level. Thus, the series of boundaries defines a series of concentric or annular areas around the home location, each annular area associated with a different range of charge values ​​(i.e., the charge values ​​associated with the two adjacent boundaries defining the annular area). For example, while the home location is reachable using up to 20% of the charge enclosed by the 20% boundary, the annular area enclosed between the 20% boundary and the 40% boundary represents additional locations that are reachable using up to 40% of the charge.

[0159] The boundaries of the enclosed reachable area for a given charge level can be determined by any suitable method, including, for example, the method described in WO 2014 / 001565. Generally speaking, for the purposes of the present invention, a one-to-many search algorithm can be used to determine the boundaries around a given node (e.g., a home location) for a particular value of a constraint parameter. The one-to-many search algorithm explores many possible links extending away from a single node and assigns a cost in terms of the constraint parameter to each link, such that each route consisting of a series of connected links has an associated cumulative cost corresponding to the cost associated with traversing each link along the route. Thus, any given point at the end of a route is determined to be reachable as long as the cumulative cost does not exceed a specific threshold related to the initial value of the parameter at that node. Thus, a set of points that are just reachable using a particular value of the parameter is used to determine a specific boundary associated with that value of the parameter. These maximally reachable point locations can be connected to define a boundary, for example, for visualization purposes, as described in more detail below with respect to step 105.

[0160] For example, where the constraint parameter is the charge level of the electric vehicle (as in the specific embodiment described above), the search algorithm proceeds by searching the map to explore the links extending from the node and assigning a cost in terms of charge level (i.e., the amount of charge required to traverse the link). For the specific case of charge, it will be appreciated that, for example, if the electric vehicle is traveling downhill, the battery can be recharged, so that the cost associated with the link can be positive or negative. Thus, any given route from a node to a specific point on the map has an associated cost that represents the cumulative cost of traversing each of the links along the route. Assuming a specific charge level at the node, the point is determined to be reachable as long as the cumulative cost to reach it from the node does not exceed the charge level at the node. The set of points that are reachable with a specific charge level defines a boundary associated with that charge level. It will be appreciated that determination of the reachable boundary can proceed similarly where the parameter is not charge level. For example, where the constraint parameter is time, the time taken to traverse each link, and therefore the total time to traverse each route, may be used to determine the boundaries.

[0161] The determination of the reachable area can also be based on one or more routing criteria. That is, the search algorithm can also take into account the navigation system's routing preferences and constraint parameters. For example, the routing algorithm may guide the user along the route with the shortest travel time or distance, or the route that is most energy- or fuel-efficient, or may guide the user away from specific road types. The routing criteria can be defined in terms of cost for the routing function. For example, if the routing criterion is to determine the fastest route between a node and a specific point, each link can be assigned a cost based on the time spent traveling along the link, and a route can be selected based on a series of links that minimizes the cumulative travel time along the route. Other routing criteria may assign a cost based on, for example, the length of the link, the average speed along the link, or the expected fuel or energy consumption associated with traversing the link. Therefore, a suitable search algorithm that takes into account routing preferences and constraint parameters may involve assigning a first cost in terms of a parameter (i.e., charge) to each link and a second cost using a cost function associated with the routing algorithm, such that each route has a first cumulative cost in terms of the parameter and a second cumulative cost that is the minimum / maximum cumulative of the second costs. The reachable area is then defined by a number of points that can be reached based on the initial values ​​of the parameters along a route selected based on the route planning criteria (eg, along the shortest or fastest route).

[0162] Since the home location is generally a fixed location that does not change often, it can be assumed that the reachable area relative to the home location for a particular charge value does not change significantly. Therefore, the series of boundaries and / or reachable areas surrounding the home location determined in step 101 can be stored in the mobile device's persistent memory, such that the series of boundaries and / or reachable areas survive device reboots. The boundaries and / or reachable areas may only need to be recalculated under specific circumstances (e.g., a change in the home location or a change in map data). Therefore, the boundaries and / or series of areas determined in step 101 can be retrieved from the device's memory without having to recalculate them. This advantageously further reduces computational load.

[0163] In a second step 102, once the reachable area associated with the home location has been determined and / or retrieved, the current reachable area relative to the device's current location based on the current charge level is calculated by route searching. The determination of the current reachable area can be performed in the manner described above, optionally also taking into account the navigation device's routing preferences. For each point in the current reachable area reached during the route search, the expected remaining charge value at that point is determined based on the cost associated with reaching that point from the current location.

[0164] At step 103, for each point in the currently reachable area reached during the route search, a check is performed to determine which of the annular areas surrounding the home location (i.e., which of the adjacent boundaries within which the point is located) contains the point. A comparison is then made between the expected remaining charge level of the electric vehicle at that point and the charge level associated with the annular area / boundary within which the point is located (step 104). This comparison makes it easy to determine whether any given point in the currently reachable area is within the safe return range of the home location. For example, if the expected remaining charge level of the electric vehicle at a given road segment is 50%, and the road segment is within the 40% reachable area of ​​the home location, then the home location is reachable. However, if the road segment is within the 60% reachable area of ​​the home location, then the home location is unreachable.

[0165] If the method is run indefinitely or, for example, performed offline, these checking and comparison steps (steps 103 and 104) may be performed for each point within the currently reachable area. However, particularly where the method is performed in real time, this step may only be performed for certain of the points within the currently reachable area. Typically, the checking and comparison steps (steps 103 and 104) will be performed for each point within the currently reachable area when the route search algorithm reaches that point (i.e., while the route search (step 102) is ongoing). It will be appreciated that the checking and comparison steps (steps 103 and 104) are relatively simple and can therefore be easily performed during the route search (step 102) without significantly increasing computational load or processing time.

[0166] The safe return range is then visualized and displayed to the driver at step 105, comprising the currently reachable point from which the home location can still be reached, assuming the current charge level, as determined in step 104. Any suitable technique may be used to visualize and display the safe return range. For example, the same visualization technique used to plot the currently reachable range (e.g., the visualization technique described in WO 2014 / 001565) may be used to visualize the safe return range. The safe return range and the currently reachable range may be displayed to the driver simultaneously, or at least be available simultaneously, allowing the driver to instantly switch between the displays. Generally speaking, the currently reachable area and / or safe return range will include multiple discrete point locations. The area / range may then be formed by interconnecting these point locations, or a selected number of these point locations. For example, the visualization process may involve dividing the area surrounding the current location into multiple sectors, wherein the area is visualized using point locations from each sector. The resolution of the display may be increased by increasing the number of sectors / points used in the visualization process. This is described in WO 2014 / 001565. For ease of visualization, the discrete points used to shape the region can be connected by arcuate lines to provide a smooth region reflecting the approximate safe return range. The accuracy or confidence level associated with the safe return range can be indicated on the display using shading or coloring. For example, points close to the border of the safe return range can be shaded lighter or darker than points completely within the safe return range.

[0167] Figure 3 The diagram illustrates how the reachable area can generally be visualized. Figure 3In the scenario illustrated in , the reachable area around a node 32 is determined by interconnecting a series of maximally reachable points 33, 34. The points can be directly interconnected 36 to provide the boundaries of the reachable area. However, for ease of visualization, it is generally best to display the reachable area to the user as a smooth approximation 30. Therefore, the connections between adjacent points 33, 34 around the perimeter of the reachable area can be approximated by arcuate lines to provide a smooth representation of the reachable area 30 for display to the user. This technique can be used for both visualization of the current reachable area relative to the current location of the device and visualization of the safe return distance. If it is desired to display the reachable area or boundary around the home location, then the same or similar technique can be used.

[0168] Steps 102 to 105 are typically performed repeatedly, continuously, and in real time as the current location (and current charge level) of the electric vehicle changes. It will be appreciated that because the current location is constantly changing, the route search algorithm may not have time to explore every link or reachable point around the current location, and thus the area generated and visualized in these steps may be incomplete.

[0169] In the embodiments described above, the reachable area or boundary around the home location can be stored in persistent device memory and reused except in exceptional circumstances. Thus, the reachable area relative to the home location is determined using only static data in the map and does not take into account received live data (e.g., indicating current traffic conditions). This is effective because it can be assumed that the home location will not change, and the static data can provide a sufficient approximation of the safe return range to reduce the user's range anxiety. Storing the reachable area in persistent memory and then retrieving it for comparison with locations within the current reachable range can be advantageous. This can be particularly advantageous when performing the described techniques on a device with limited processing power (e.g., a user's smartphone) because constantly recalculating the reachable area unless necessary (e.g., to account for changes in the home location or changes in map data) can be computationally expensive. However, it is also contemplated that, for example, when the described method is applied to a server so that processing power is less limited, the reachable area and boundary around the home location can be recalculated on a more regular basis to provide a more accurate approximation (e.g., to account for current or recent traffic conditions).

[0170] Although the present invention has been described with reference to particular embodiments, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the scope of the present invention as set forth in the following claims.

Claims

1. A method of determining a first boundary enclosing a portion of a geographic area containing a navigable network, said portion representing an area reachable from a first location on the navigable network while still allowing reachability to a second location on the navigable network, assuming a parameter limiting the amount of the navigable network that can be traversed has a value, said navigable network being represented by an electronic map, said electronic map including a plurality of road segments representing navigable elements of the navigable network, said method comprising: determining a position on a road segment representing the first position and obtaining the value of the parameter at the determined position; exploring road segments of the electronic map relative to the determined location using a one-to-many route planning algorithm with an associated cost function, and for a road segment explored and determined to be reachable, wherein the road segment is reachable if a cumulative cost resulting from traversing a best-cost route from the determined location representing the first location is less than the obtained value of the parameter at the determined location; determining whether the road segment is located within a second boundary selected from a plurality of second boundaries by checking between which two adjacent second boundaries of the plurality of second boundaries the road segment is located, and comparing an expected value of the parameter at the road segment after traveling from the first location to the road segment with a value of the parameter associated with an outer second boundary of the two adjacent second boundaries between which the road segment is located; wherein each of the plurality of second boundaries encloses a portion of the geographic area around the second location, and wherein each of the plurality of second boundaries is associated with a different value of the parameter and represents an area from which the second location can be reached assuming the parameter has the associated value, The method further includes determining the first boundary using the road segments determined to be within the second boundary. The method of claim 1 , wherein the first location is a current location of a user or a mobile device. The method according to claim 1 , wherein the second position is a predetermined position. The method of claim 3 , wherein the predetermined location is a home location.

5. The method of claim 1 or 2, further comprising receiving a selection of a location, and setting the selected location as the second location.

6. The method of claim 1 or 2, wherein data indicative of the plurality of second boundaries is stored in a memory, and the method further comprises accessing the stored data to retrieve data indicative of the second boundaries.

7. The method of claim 1 or 2, further comprising determining the plurality of second boundaries, wherein the determining of second boundaries for predetermined values ​​of the parameter comprises: determining a position on the road segment representing the second position; and A one-to-many route planning algorithm having an associated cost function is used to explore the road segments of the electronic map relative to the determined location, and for the explored road segments, it is determined whether the location representing the second location is reachable from the road segments assuming the parameter has the predetermined value.

8. The method according to claim 1 or 2 further includes at least one of the following: (i) displaying information representing at least some of the first boundary or the area enclosed by the first boundary on a display; and (ii) transmitting the information representing at least some of the first boundary or the area enclosed by the first boundary to a mobile device for display thereon.

9. The method of claim 1 or 2, further comprising determining a third boundary enclosing a portion of the geographic area around the first location, the portion representing an area reachable from the first location assuming that the parameter at the first location has the obtained value.

10. The method according to claim 9 further includes at least one of the following: (i) displaying information representing at least some of the third boundary or the area enclosed by the third boundary on a display; and (ii) transmitting the information representing at least some of the third boundary or the area enclosed by the third boundary to a mobile device for display thereon.

11. A system for determining a first boundary enclosing a portion of a geographic area containing a navigable network, the portion representing an area reachable from a first location on the navigable network while still allowing reachability to a second location on the navigable network, assuming a parameter limiting the amount of the navigable network that can be traversed has a value, the navigable network being represented by an electronic map including a plurality of road segments representing navigable elements of the navigable network, the system comprising: means for determining a position on a road segment representing said first position and obtaining said value of said parameter at said determined position; Widgets for: exploring road segments of the electronic map relative to the determined location using a one-to-many route planning algorithm having an associated cost function, and for a road segment explored and determined to be reachable, the road segment is reachable if a cumulative cost resulting from traversing a best-cost route from the determined location representing the first location is less than the obtained value of the parameter at the determined location; determining whether the road segment is located within a second boundary selected from a plurality of second boundaries by checking between which two adjacent second boundaries of the plurality of second boundaries the road segment is located, and comparing an expected value of the parameter at the road segment after traveling from the first position to the road segment with a value of the parameter associated with an outer second boundary of the two adjacent second boundaries between which the road segment is located; Each of the plurality of second boundaries encloses a portion of the geographic area around the second location, and wherein each of the plurality of second boundaries is associated with a different value of the parameter and represents an area from which the second position can be reached assuming the parameter has the associated value; and Means for determining the first boundary using the road segments determined to be within the second boundary.

12. A computer program product comprising computer readable instructions which, when executed by at least one processor of a system, cause the system to perform the method according to any one of claims 1 to 10.

13. The computer program product of claim 12, wherein the computer-readable instructions are stored on a non-transitory computer-readable medium.

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