SPEED CONTROL SYSTEM AND SPEED CONTROL METHOD FOR CURVED ROAD SECTIONS

Abstract

Speed ​​control system for a curved road section, which features: a radio communication module (15) that supports communication with roadside units (1) and receives road information for multiple points on a curved road adjacent to the roadside units from the roadside units (1); a calculation unit (25) for permissible speed, which calculates permissible maximum speeds, which are the highest speeds at which a vehicle travels, for the multiple points using the road information; a calculation unit (30) for optimal speed, which calculates an optimal speed of the vehicle within an acceleration and deceleration range set taking into account a predetermined acceleration and deceleration limit of the vehicle; and a control module (20) that displays the optimal speed calculated by the calculation unit (30) for optimal speed or that provides the calculated optimal speed to another control system in the vehicle in such a way that the speed of the vehicle is controlled, wherein the road information includes the number of points received by one of the roadside units (1), and The control module (20) predicts, according to the number of points, how much the curved road changes.

Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit under 35 USC § 119(a) of Korean Patent Application No. 10-2014-0134305, filed on October 6, 2014, which is hereby incorporated by reference for all purposes as if fully disclosed herein. BACKGROUND OF THE INVENTION 1. Field of the Invention

[0002] The present invention relates to a speed control system for a curved road section, and more particularly, to a technology that calculates the maximum allowable speed and an optimum speed on a curved road using information supplied from a roadside unit and the like to present it to the driver or to control a vehicle speed so that the vehicle can be driven stably and the driver's safety can be ensured on a curved road section. 2. Description of the state of the art

[0003] In modern societies, as vehicle use has increased dramatically, hundreds of millions of people are killed or injured each year due to vehicle accidents. Accordingly, various vehicle technologies have been developed to reduce injuries and economic losses caused by traffic accidents. These technologies include automatic cruise control (ACC) technology, lane change assistance technology, lane departure warning technology, and parking assistance technology.

[0004] However, since these technologies use sensors, cameras, or the like installed in vehicles, their detection range and effects are limited. Accordingly, technologies for detecting a driving environment in a wider range have been developed. One of these is V2X technology. V2X is the acronym for "Vehicle to Everything" and includes V2V (Vehicle to Vehicle), V2I (Vehicle to Infrastructure), and V2N (Vehicle to Nomad). Here, the infrastructure includes a roadside unit (RSU) installed on one side of the road to communicate with the vehicles. The vehicles communicate with the roadside units installed near the road to form a network to ensure traffic safety, receive various information from the roadside units, guide roads, and deliver information such as various multimedia content, and prevent traffic congestion.

[0005] The vehicle speed should be increased or decreased according to the degree of curvature of a curved road while the vehicle is being driven. It is difficult to increase or decrease the vehicle speed appropriately because the field of view is small due to the characteristics of the curved road. Accordingly, maintaining a safe speed on a curved road requires prompt judgment and driving skill from the driver. Accordingly, to ensure vehicle safety on a curved road, it is necessary to provide appropriate information to adjust the driver's vehicle speed using roadside units that can detect a relatively wide driving environment.

[0006] Systems and methods for speed control in curved road sections are known in the state of the art.

[0007] DE 102 10 546 A1 shows a method for automatic vehicle guidance in which infrastructure data are transmitted wirelessly to the vehicle and commands for the vehicle guidance are calculated on the basis of the infrastructure data, wherein the infrastructure data for at least one immediately preceding section of the route are loaded into a vehicle's own memory, the current position of the vehicle is continuously determined using a positioning system and the commands are calculated on the basis of the position data and the stored infrastructure data.

[0008] DE 10 2008 035 115 A1 discloses a system and method for detecting a road curve as a vehicle approaches the curve, automatically providing road curvature information, and controlling the vehicle's speed. The system uses a tracking device and a map database to determine the vehicle's position. Depending on the vehicle's speed, the system generates a curvature profile for various curvature data points in front of the vehicle at or around the curve. The target speed profile and the actual vehicle speed are compared at each profile point to determine whether the vehicle is traveling too fast for the target speed. The acceleration calculation can be improved by providing a driver cornering mode input, which the vehicle operator can select based on how aggressively the driver wants the system to slow the vehicle.

[0009] US 2010 / 0 292 904 A1 shows a vehicle travel control system with a speed pattern generation unit that generates a speed pattern according to a target travel path, a travel control unit that controls the travel of the vehicle based on the speed pattern, a first speed condition correction unit that corrects speed conditions in a direction from a start position of the travel control to an end position of the travel control on the target travel path, and a second speed condition correction unit that corrects speed conditions in a direction from the end position of the travel control to the start position of the travel control on the target travel path.

[0010] DE 10 2006 028 277 A1 shows a device for advance warning of curves with a control unit which is connected to a memory containing map data and which determines a current position by means of position determination means, wherein for a predeterminable section of the route ahead a curvature of the route can be calculated on the basis of the map data and a curve target speed can be calculated and displayed as a recommendation on the basis of the curvature and an input value which can preferably be entered by an operator by means of input means. SUMMARY OF THE INVENTION

[0011] The present invention provides a speed control system for a curved road section for calculating a maximum allowable speed and an optimum speed on a curved road using information supplied from a roadside unit and the like to supply it to the driver or to automatically control a vehicle speed so that the vehicle can be driven stably and the safety of the driver on a curved road section can be ensured.

[0012] According to one aspect of the present invention, there is provided a speed control system for a curved road section, including: a radio communication module that supports communication with roadside units and receives road information for a plurality of points on a curved road adjacent to the roadside units from the roadside units; a permissible speed calculation unit that calculates the permissible maximum speeds, which are the highest speeds at which a vehicle is driven, for the plurality of points using the road information; an optimal speed calculation unit that calculates an optimal speed within an acceleration and deceleration range set in consideration of a predetermined acceleration and deceleration limit of the vehicle;and a control module that externally displays the optimal speed calculated by the optimal speed calculation unit or supplies the calculated optimal speed to another control system in the vehicle, thereby controlling the speed of the vehicle. The road information includes the number of points received from one of the roadside units. The control module predicts the degree of curved road changes based on the number of points.

[0013] According to another aspect of the present invention, there is provided a speed control method for a curved road section, which includes: receiving road information for a plurality of points on a curved road adjacent to roadside units from the roadside units; calculating permissible maximum speeds at the plurality of points; calculating an optimal speed of the vehicle in an acceleration and deceleration range set in consideration of a predetermined acceleration and deceleration limit of the vehicle; and controlling the vehicle such that the speed of the vehicle is changed by displaying the optimal speed to the outside or by supplying the optimal speed to another control system in the vehicle. The road information includes the number of points received from one of the roadside units.The control module predicts how much the curved road will change based on the number of points.

[0014] The curved road section speed control system according to the present invention receives the curvature information of a curved road section using the roadside units, calculates permissible maximum speeds at which the vehicle can be driven in the curved sections using the information, and calculates optimal speeds that do not exceed the permissible maximum speeds so that the vehicle can be driven stably in a curved section. Accordingly, the vehicle can be driven stably, and the driver has a safe and comfortable feeling while driving the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings in which: Fig. 1 is a block diagram of a speed control system for a curved road section according to the present invention; Fig. Figure 2 is an exemplary view of a curved road section; Fig. 3 is a diagram showing the maximum permissible speed and the optimum speed when maximum permissible speeds are calculated on the center lines corresponding to the points of Fig. 2 are calculated, changed; Fig. 4 is a flowchart showing a process of controlling the speed in a curved road section by communication with a roadside unit in a speed control system for a curved road section according to Fig. 1 illustrated; and Fig. Figure 5 is a diagram showing a change in the maximum permitted speeds and the optimal speeds calculated in road sections or at points. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] Hereinafter, some embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same components are denoted by the same reference numerals even though they are shown in different drawings. Furthermore, in the following description of the present invention, a detailed description of known functions and configurations included therein will be omitted if doing so would impair the clarity of the subject matter of the present invention.

[0017] Additionally, terms such as first, second, A, B, (a), (b), or the like may be used herein when describing components of the present invention. These terms are used merely to distinguish one structural element from other structural elements, and a property, order, sequence, and the like of a corresponding structural element are not limited by the term. It should be noted that when the description states that one component is "connected," "coupled," or "joined" to another component, a third component may be "connected," "coupled," and "joined" between the first and second components, although the first component may be directly connected, coupled, or joined to the second component.

[0018] Fig. 1 is a block diagram of a speed control system for a curved road section according to the present invention. Fig. 2 is an exemplary view of a curved road section.

[0019] The curved road section speed control system 10 according to the present invention calculates a permissible maximum speed at which the vehicle can be driven in a curved section using information supplied from a roadside unit 1, and calculates an optimal speed at which the vehicle can be optimally driven based on the calculated permissible maximum speed, so that the vehicle can be guided to be driven at an optimal speed and thus driven safely.

[0020] The speed control system 10 for a curved road section may include: a radio communication module 15 for radio communication with an external device such as a roadside unit 1; a permissible speed calculation unit 25 that calculates permissible maximum speeds of the vehicle at points of a curved road using information obtained by the roadside unit 1; an optimal speed calculation unit 30 that calculates an optimal speed that does not exceed the permissible maximum speed, taking into account the preset limits of acceleration and deceleration of the vehicle; and a control module 20 that controls operations of the components including the radio communication module 15 and generates a command signal such that the driving of the vehicle can be controlled according to the optimal speed.

[0021] It has been described that an example of an external device that can supply required information to the speed control system while communicating with the speed control system 10 is the roadside unit 1, but the present invention is not limited to this, and the external device includes all types of vehicles that supply road information (an altitude and a latitude, radius information, and the like) required for calculating a permissible maximum speed according to the present invention.

[0022] The radio communication module 15 supports a communication method for radio communication with the roadside unit 1, and the roadside unit 1 and the radio communication module 15 can communicate with each other in a dedicated short-range, high-speed packet communication scheme called Dedicated Short Range Communication (DSRC). The DSRC communication scheme uses bidirectional short-range communication between the roadside unit 1 and the radio communication module 15, a one-to-multiple communication function, a communication environment that maintains a line-of-sight, a high-speed transmission function, and a low-cost and simple modulation technology.

[0023] The radio communication module 15 receives information about the latitude, altitude, and radii of a plurality of points from the roadside unit 1 while communicating with the roadside unit 1, and the corresponding information is provided to the speed limit calculation unit 25. Here, the plurality of points are points located within a predetermined radius from the roadside unit 1, and they may be points whose radii vary on a curved road.

[0024] When the roadside unit 1 selects the points, it selects a location of a road side at which the radius thereof is changed on a curved road, draws a vertical line toward the center of the road from the location of the road side corresponding to the radius, and determines the location point at which the vertical line and the center line of the road meet.

[0025] Among the information provided by the roadside unit 1, the radius information represents a degree by which the curved road is curved, and it can have a (+) or (-) value according to the direction of curvature at the point. For example, as shown in Fig. 2, the curved road at point 1 and point 2 is curved to the right and indicated by (+), and the curved road at point 3 and point 4 is curved to the left and indicated by (-). In contrast, the radii at point 1 and point 2 may be indicated by (-), and the radii at point 3 and point 4 may be indicated by (+). The radius information may be contained in a 16-bit data packet.

[0026] The latitude and altitude are required to determine a location and degree of curvature of a curved road, and they can be contained in data packets of 32 bits each.

[0027] The radio communication module 15 can receive information regarding the number of points provided from the roadside unit 1 to the vehicle, along with information about the latitudes, altitudes, and radii from the roadside unit 1. Accordingly, the control module 20 can compare the number of pieces of information actually received from the roadside unit 1 with the number of points provided by the roadside unit 1 and can determine whether information about all points has been received.

[0028] In general, since the range that can be detected by the roadside unit 1 has been determined, the amount of change of the curved road can be predicted according to the number of points detected by the roadside unit 1. That is, when the number of points detected by the roadside unit 1 is larger, it can be predicted that the curved road changes more.

[0029] The roadside units 1 are communication devices installed at a predetermined distance (for example, 1 km) on the road, and they are identified by unique ID and store information (the curvature of the road, radius information, and the like) about the road area covered by the roadside units 1, in addition to information (altitudes and latitudes) about the locations thereof, and broadcast the information to the outside at a predetermined interval.

[0030] When the permissible speed calculation unit 25 receives information about latitudes, altitudes, and radii of a plurality of points from the roadside unit 1, it can calculate permissible maximum speeds at which the vehicle can be driven at maximum speeds at points, and can supply the calculated permissible maximum speeds to the optimal speed calculation unit 30.

[0031] The permissible maximum speeds can be calculated based on values ​​obtained by multiplying the radii R of several points and a permissible maximum lateral speed ay.

[0032] For example, the permissible speed calculation unit 25 calculates the permissible maximum speeds at the points using Equation 1, by which a lateral acceleration is obtained. ay=V2R

[0033] In Equation 1, V denotes a permissible maximum speed, R denotes a radius, and ay denotes a lateral acceleration. Here, the radius R is obtained from the roadside unit 1, and the permissible lateral acceleration ay is predetermined by the designer.

[0034] Accordingly, the permissible speed calculation unit 25 obtains a permissible maximum speed at which the lateral acceleration ay is less than a predetermined value. For example, if the permissible maximum lateral acceleration ay is set to 0.3 g, the permissible speed calculation unit 25 can obtain a permissible maximum speed when the lateral acceleration ay is less than 0.3 g.

[0035] For example, if the maximum lateral acceleration ay is set to 0.3 g, the permissible speed calculation unit 25 can calculate the permissible maximum speed V according to Equation 2. V=0.3R

[0036] The optimal speed calculation unit 30 can calculate the optimal target speed of the vehicle using the permissible maximum speeds at the points obtained by the permissible speed calculation unit 25.

[0037] The optimal speed calculation unit 30 can calculate an optimal speed such that the allowable maximum speed is not exceeded, taking into account the limits of preset acceleration and deceleration, and a range within which the optimal speed can be changed, that is, the range of a slope value of the speed change or the acceleration / deceleration value is set in advance taking into account the limits of acceleration and deceleration.

[0038] Here, the acceleration and deceleration limits are set experimentally by measuring the acceleration and deceleration ranges in which the driver feels comfortable when accelerating and decelerating the vehicle, and by limiting the maximum acceleration and deceleration ranges. Generally, it is preferable to consider the maximum range in which the vehicle can accelerate and decelerate according to the vehicle type and model.

[0039] Generally, when considering the physical limits or driving comfort of a vehicle, the upper limit of acceleration that can be exerted by the vehicle can be set to approximately +0.1 g, and the upper limit of deceleration can be set to approximately -0.3 g. In this case, the optimal speed calculation unit 30 calculates an optimal speed based on the maximum allowable speed within a range that does not deviate from the acceleration and deceleration range.

[0040] The procedure for calculating the maximum permissible speed and the optimum speed is described in detail with reference to Fig. 5 described.

[0041] The control module 20 operates the radio communication module 15 to control the radio communication module 15 such that the radio communication module 15 transmits and receives information to and from the roadside unit 1. If information is not automatically obtained from the roadside unit 1, a request for information about the number of points, along with information about the altitudes, latitudes, and radii of the points, may be made by the radio communication module 15 to the roadside unit 1. The control module 20 may supply the information supplied by the roadside unit 1 to the permissible speed calculation unit 25.

[0042] When the permissible speed calculation unit 25 calculates the permissible maximum speeds for the points, the control module 20 may compare the permissible maximum speeds for the neighboring points. That is, with reference to Fig. 2, the permissible maximum speed for point 3 is obtained, and the control module 20 compares the permissible maximum speed with the permissible maximum speed for point 2. If the permissible maximum speeds for point 2 and point 3 are the same or differ by a degree less than a predetermined value in the comparison result, the control module 20 can control the maximum speed calculation unit 30 so that the maximum speed calculation unit 30 does not calculate the optimal speed. The function of the control module 20 is prepared against a case in which the roadside unit 1 provides information about a point other than the points at which the radii thereof are changed.Accordingly, if the roadside unit 1 sends information only about a point at which the radius thereof is changed, the control module 20 does not need to compare the permissible maximum speeds of the points.

[0043] The control module 20 can guide the driver to change the vehicle speed to the corresponding optimal speed by displaying the optimal speed calculated by the optimal speed calculation unit 30 to the driver. Together, the control module 20 can automatically control the vehicle speed by providing a command signal to an engine control unit for automatically controlling the vehicle speed.

[0044] When the driver directly changes the vehicle's speed, the control module 20 can externally display the optimal speed through a navigation system, a display unit, a human-machine interface (HMI), or the like, or can provide a voice signal to the driver. Then, the control module 20 guides the driver to ensure the vehicle reaches the optimal speed to the next point by displaying the optimal speed of the next point each time the vehicle reaches the points.

[0045] Fig. 3 is a diagram showing the maximum permissible speed and the optimum speed when the speeds on the center lines corresponding to the points of Fig. 2 calculated maximum permissible speeds may be changed.

[0046] As illustrated, when calculating the maximum allowable speeds for the points, the speed changes of the points are set to change linearly. When calculating the optimal speeds for the points, the speed changes of the points can also be set to change linearly to achieve the optimal speeds.

[0047] Accordingly, as in Fig. 3, when an optimal speed at one point is changed to an optimal speed at the next point, the control module 20 may generate a command signal such that the speed of the vehicle is changed linearly, and may provide the command signal to an engine control unit.

[0048] An operation of controlling a speed in a curved road section by communicating with the roadside unit 1 in the speed control system 10 in a curved control section will be described with reference to Fig. 4 described.

[0049] When the roadside unit 1 is detected and information at the points is not received by the roadside unit 1, the control module 20 may request information about the number of roadside units 1 together with information about altitudes, latitudes and radii from the roadside units 1 through the radio communication module 15.

[0050] When the control module 20 receives the corresponding information from the roadside unit 1 (S400), the control module 20 supplies the radius information to the permissible speed calculation unit 25, and calculates the permissible maximum speed of the vehicle whose lateral acceleration is smaller than a predetermined value using the radius information of the points (S410).

[0051] When the permissible speed calculation unit 25 calculates the permissible maximum speeds for the points, the control module 20 compares the permissible maximum speeds at the points with the permissible maximum speeds at the neighboring points, and only when the permissible maximum speed is changed in the comparison result, provides the corresponding permissible maximum speeds to the optimal speed calculation unit 30 to actuate the optimal speed calculation unit 30. This process can be omitted if the roadside units 1 only provide information for the points where their radii are changed.

[0052] The optimal speed calculation unit 30 calculates optimal speeds at points taking into account the acceleration and deceleration limits of the vehicle (S420).

[0053] The calculated optimal speeds at the points are supplied to the control module 20, and the control module 20 displays the optimal speeds to the outside so that the driver recognizes the optimal speeds according to the function of the vehicle (S430), or automatically controls the speed of the vehicle by supplying the optimal speeds to the engine control module 20 of the vehicle (S435).

[0054] Fig. Figure 5 is a graph showing a change in the maximum permissible speeds and the optimal speeds calculated in road sections or at points.

[0055] The solid line in Fig. 5 indicates a maximum permissible speed, and the dashed line in Fig. 5 indicates an optimal speed.

[0056] Assuming a road environment according to Fig. 2, permissible maximum speeds for road sections between points are calculated based on location information and radius information of points 1 to 4.

[0057] The maximum permissible speeds are constant values ​​at the points and are different at the points. Accordingly, as shown by the solid line in Fig. 5, the maximum permissible speeds for several points or road sections are discrete values.

[0058] However, since the actual speed of the vehicle cannot be changed discretely, the optimal speeds are calculated such that the speed of the vehicle changes continuously within the acceleration and deceleration range that takes into account the physical characteristics of the vehicle and the comfort of the driver.

[0059] As in Fig. 5, the permissible maximum speed in a road section near point 1 is determined to be V1, and the permissible maximum speed in a road section near point 2 is determined to be V2, and the two permissible maximum speeds are discontinuously changed.

[0060] Then, since the speed control system can calculate the maximum allowable speeds for the road sections the driver will next travel using information from the roadside units, it can recognize that the maximum allowable speed will be changed to V at a predetermined later time while the vehicle is traveling at point 1.

[0061] Accordingly, the speed control system calculates an optimal speed such that the vehicle starts to decelerate at point A near point 1, so that the optimal speed, which is an actual target speed, can be continuously changed.

[0062] That is, the dashed line that starts at point A of Fig. 5 indicates the optimal speed, and the slope of the dashed line should be within the acceleration and deceleration range (-0.3 g to 0.1 g) taken into account when calculating the optimal speed.

[0063] In this way, the speed control system 10 according to the present invention receives curvature information about a curved road section using the roadside units 1, calculates permissible optimal speeds at which the vehicle can be driven in the curved sections using the information, and calculates optimal speeds that do not exceed the permissible maximum speed so that the vehicle can be driven stably in a curved section. Accordingly, the vehicle can be driven stably, and the driver can feel safe and comfortable while driving the vehicle.

[0064] In the above-described embodiment of the present invention, the standard contents or standard documents are omitted to keep the description brief, and they form part of the description. Accordingly, it should be noted that the process of adding some of the contents of the standard contents and standard documents to the description or claims falls within the scope of the present invention.

[0065] Although the embodiments of the present invention have been described for illustrative purposes, it will be apparent to those skilled in the art that various modifications, additions, and substitutions are possible without departing from the scope and spirit of the invention. Therefore, exemplary aspects of the present disclosure have not been described for the purpose of limitation. The scope of the present invention should be interpreted based on the accompanying claims in such a manner that all technical ideas included within the range equivalent to the claims belong to the present invention.

Claims

[1] Speed control system for a curved road section, comprising: a radio communication module (15) that supports communication with roadside units (1) and receives road information for a plurality of points on a curved road adjacent to the roadside units from the roadside units (1); a permissible speed calculation unit (25) that calculates permissible maximum speeds, which are the highest speeds at which a vehicle travels, for the plurality of points using the road information; an optimum speed calculation unit (30) that calculates an optimum speed of the vehicle in an acceleration and deceleration range set in consideration of a predetermined acceleration and deceleration limit of the vehicle; and a control module (20) which displays the optimum speed calculated by the optimum speed calculation unit (30) or supplies the calculated optimum speed to another control system in the vehicle such that the speed of the vehicle is controlled, wherein the road information comprises the number of points received by one of the roadside units (1), and the control module (20) predicts how much the curved road changes according to the number of points. [2] The speed control system according to claim 1, wherein the road information at the plurality of points includes at least one of the information about the altitudes, latitudes and radii of the curved road at the plurality of points. [3] A speed control system according to claim 1 or 2, wherein the plurality of points are located within a predetermined radius from the roadside units (1), and the points are points at which straight lines extending vertically from a location on a roadside where the radius of the road changes toward the center of the road meet the center line of the road. [4] A speed control system according to any one of claims 1 to 3, wherein the permissible speed calculation unit (25) calculates the permissible maximum speeds based on values obtained by multiplying the radii (R) of the plurality of points and a permissible maximum lateral acceleration (ay). [5] A speed control system according to any one of claims 2 to 4, wherein the radius information is indicated by (+) or (-) depending on whether the plurality of roads are curved to the right or to the left, and is supplied by the roadside units. [6] A speed control system according to any one of claims 1 to 5, wherein the optimum speed calculation unit (30) calculates the optimum speed within a range of an inclination value of a speed change set in consideration of the acceleration and deceleration limit of the vehicle. [7] A speed control system according to any one of claims 1 to 6, wherein the optimum speed calculation unit (30) calculates the optimum speed such that the optimum speed is continuously changed between two permissible maximum speeds. [8] A speed control system according to any one of claims 1 to 7, wherein the control module (20) generates a command signal for controlling the running of the vehicle such that an optimum speed is linearly changed from a point at which the optimum speed thereof is calculated to another point. [9] A speed control system according to any one of claims 1 to 8, wherein the control module (20) indicates the optimum speeds at each of the points using at least one of an image signal and a voice signal. [10] A speed control method for a curved road section, comprising: Receiving road information from the roadside units (1) for a plurality of points on a curved road adjacent to the roadside units; Calculating permissible maximum speeds at the multiple points; Calculating an optimal speed of the vehicle in an acceleration and deceleration range set taking into account a predetermined acceleration and deceleration limit of the vehicle; and Controlling the vehicle in such a way that the speed of the vehicle is changed by indicating the optimal speed or by delivering the optimal speed to another control system in the vehicle, wherein the road information comprises the number of points received by one of the roadside units (1), and the speed control method further comprises predicting how much the curved road changes according to the number of points.

Images