Positioning and guiding system for farmland community planning

Abstract

The invention relates to the field of surveying and mapping geographic information and intelligent agriculture, and discloses a positioning and guiding system for farmland community planning, and the method and the system utilize a high-precision data acquisition module and a portable controller to accurately acquire and record an irregular boundary point sequence of a to-be-planned plot; then, on the controller, according to a standard cell size set by a user and a planned datum line direction angle, a theoretical grid is automatically generated; and the grid is geometrically cut by taking an actually measured boundary as a contour, effective cell vertexes located in the boundary are screened out, and a digital planning scheme which completely adapts to the actual shape of the land parcel is formed. In the lofting stage, the system compares the current position with the selected target vertex in real time, provides dynamic navigation guidance including the distance and the direction, and triggers multi-sensory arrival prompts such as sound and light when the distance between the current position and the selected target vertex is smaller than a preset precision threshold value. According to the method, surveying and mapping, planning and lofting are integrated, and high automation and intelligence of the operation process are achieved.

Description

Technical Field

[0001] This invention relates to the fields of surveying and mapping geographic information and smart agriculture technology, specifically a positioning guidance system for farmland planning. Background Technology

[0002] In fields such as land resource management, modern agricultural production, and engineering construction, it is often necessary to divide a large, irregularly shaped plot of land into multiple regular internal sub-plots or units according to standardized dimensions. This standardized division not only facilitates refined management and optimized resource allocation but is also an important prerequisite for subsequent large-scale mechanized operations, automated irrigation, and precision agriculture practices. For example, in agricultural planting, dividing a large field into uniformly sized sub-plots facilitates independent fertilizer and water management, crop growth monitoring, and yield assessment in different sub-plots.

[0003] Traditional land delineation relies heavily on professional surveyors. They typically use optical surveying instruments such as total stations to perform tedious angle and distance measurements on-site, then determine the coordinates of each plot's vertices through manual calculations or with the aid of simple calculation tools, and finally stake out each point. The entire process is technically demanding, requires collaboration from multiple people, consumes a significant amount of manpower and resources, and is time-consuming and inefficient, making it difficult to meet the demands of modern agriculture for rapid and flexible responses.

[0004] With the development of Global Navigation Satellite Systems (GNSS), especially Real-Time Dynamic Differential (RTK) technology, the accuracy and efficiency of field data acquisition have been revolutionaryly improved, making it possible for a single person to quickly obtain coordinates with centimeter-level accuracy. However, in current technical practices, this high-precision positioning capability has not been seamlessly integrated with the internal planning and design process of a site. The usual practice is that operators first use RTK equipment to survey the site boundaries, then import the collected boundary data into professional desktop CAD or GIS software in the office. Technicians then complete the planning and design of the area on a computer, calculate the coordinate list of all vertices to be staked out, and finally export these coordinate points, re-import them into the handheld RTK equipment, and the operators return to the site to stake out the points one by one based on the coordinates of the target points in the equipment.

[0005] While this process represents an improvement over traditional methods, its operational model still exhibits significant inherent fragmentation. Measurement, design, and layout are treated as three independent stages, requiring data to be repeatedly transferred between field acquisition equipment and office computers. This not only makes the operation cumbersome and error-prone but also significantly extends the overall project cycle. This model heavily relies on specialized software and designers in the office, lacking the flexibility and immediacy of on-site operations, and failing to meet the integrated needs of operators for "instant measurement, planning, and layout" on-site. When on-site conditions necessitate adjustments to the planning scheme, the entire process must be repeated, resulting in slow response times and severely hindering operational efficiency. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a positioning guidance system for farmland plot planning. It aims to solve the technical problem that in existing land plot division technologies, the on-site measurement, indoor planning, and field layout processes are disconnected, resulting in a cumbersome and inefficient overall workflow and the inability to achieve integrated and rapid on-site operations.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a positioning guidance system for farmland planning, comprising: a high-precision data acquisition module, a data processing and planning module, and a real-time positioning and guidance module.

[0008] The high-precision data acquisition module is designed to acquire geospatial information of farmland to be planned. Specifically, this module collects and records the geodetic coordinates of multiple farmland boundary points, which together constitute the farmland boundary representing the farmland's extent. In a preferred embodiment, this module may employ a real-time dynamic differential device based on a Global Navigation Satellite System (GNSS) to obtain three-dimensional geodetic coordinates with centimeter-level accuracy, including longitude, latitude, and geodetic height.

[0009] The data processing and planning module, which communicates with the high-precision data acquisition module, is the core of this system's computation. This module performs the following functions: First, this module converts the geodetic coordinates of the collected farmland boundary points into local plane coordinates. To facilitate planar geometric calculations, the spherical coordinates need to be projected onto a plane. One feasible implementation is to use the Gauss-Kruger projection or UTM projection method to convert the geodetic coordinates of each farmland boundary point... Convert to two-dimensional coordinates in local plane coordinate system .

[0010] Secondly, based on the planning parameters input by the user and combined with the farmland boundaries converted to local plane coordinates, the module generates one or more vertices of a plot through algorithmic calculations. These vertices together constitute the plot vertex coordinate set. The planning parameters typically include the standard plot width, standard plot length, and planning baseline orientation angle. The planning baseline orientation angle can be automatically determined by the user by selecting any two points on the farmland boundary, or it can be specified by the user by directly inputting a specific angle value.

[0011] In the specific implementation of generating cell vertices, this module first determines the orientation angle of the planning baseline set by the user. Construct a set of orthogonal unit basis vectors: principal direction unit vectors unit vector in the normal direction Then, starting from a calculation point... Using a base point, a theoretically infinitely large grid is generated using the following formula, with its grid vertices... The coordinates are calculated as follows: ; in, This represents the standard width of the aforementioned cell. This represents the standard length of the cell. and This is an integer index that increases or decreases along the principal and normal directions. Finally, the module performs Boolean operations (e.g., clipping operations) on this theoretical mesh and the closed polygon formed by the farmland boundary, filtering and retaining all theoretical mesh vertices located inside or on the boundary of the polygon, thus forming the final valid set of cell vertex coordinates.

[0012] The real-time positioning and guidance module connects to the data processing and planning module and utilizes the real-time positioning function of the high-precision data acquisition module to assist users in accurate on-site layout. This module performs the following functions: First, the module obtains the user's current location on site and converts it into local planar coordinates. When the user selects a target point from the pre-generated set of cell vertex coordinates on the system interface, the module calculates and provides navigation guidance information from the current location to that target point in real time.

[0013] In one specific embodiment, the navigation guidance information includes at least the straight-line distance from the current location to the target point. This distance can be calculated using the following formula: ; in, The local plane coordinates of the selected target point are , and This provides the real-time local plane coordinates of the user's current location.

[0014] To provide more intuitive guidance, navigation guidance information may also include the target azimuth, used to indicate the direction of the target point relative to the current location in graphical or numerical form. This is when the calculated straight-line distance... When the accuracy is less than a preset threshold (e.g., 5 cm), the system can automatically send an arrival notification to the user, indicating that the target point has been accurately reached and marking can be performed.

[0015] This invention provides a positioning guidance system for farmland plot planning. It has the following beneficial effects: 1. This invention creatively integrates three previously independent steps—boundary surveying, site planning, and vertex setting—that required repeated movement between the field and the office, into a portable system that can be operated by a single person. After completing boundary data collection on-site, the operator can immediately begin planning and design and set-out work on the same device without any data import or export. This closed-loop "measure, plan, and set out" work mode completely eliminates data transfer delays and spatial relocation costs in traditional processes, fundamentally improving the continuity and overall efficiency of the work.

[0016] 2. Traditional land planning heavily relies on technicians performing tedious manual drawing and calculations in professional CAD or GIS software. This invention, through its built-in core planning algorithm, transforms this complex intellectual labor into simple parametric input. Operators only need to input the length and width of the plot and the desired working direction angle, and the system can automatically complete the construction of the theoretical grid, the precise trimming calculation of the measured irregular boundaries, and instantly generate the final planning scheme. This allows even ordinary agricultural technicians without surveying or mapping backgrounds to easily complete professional-level land planning and design, greatly expanding the applicability of the technology.

[0017] 3. In actual operation, planning schemes often need to be adjusted due to the actual terrain, obstacles, or the owner's temporary ideas. This invention completely delegates planning decision-making power to on-site operators. When it is necessary to change the arrangement direction or size of the area, simply re-enter the direction angle or length and width parameters on the portable controller, and the system can complete the recalculation and layout of all vertices within seconds and display it on the screen in real time. This instant feedback and modification capability gives on-site operations unprecedented flexibility and avoids the long rework cycle caused by scheme changes in the traditional model.

[0018] 4. This invention provides an extremely intuitive navigation interface during the layout stage. Through a dynamic arrow that always points to the target and constantly updated real-time distance, the task of finding an abstract centimeter-level coordinate point is transformed into a simple follow-along process similar to a "treasure hunt." In particular, when the distance meets the preset accuracy requirements, the system triggers a multi-sensory "arrival" signal, including interface color changes, sound prompts, and equipment vibration, providing the operator with a clear, unambiguous, and unmistakable confirmation instruction. This design greatly reduces human error during the layout process, ensuring that every physical marker is accurately positioned.

[0019] 5. For the prevalent irregular plots of land, this invention uses the boundary polygons mapped on-site as rigid constraints, performing precise Boolean operations on the theoretically generated infinite grid to ensure that every vertex of the final output cell is strictly located inside the plot or on its boundary. This algorithmically guarantees that the planning scheme will not exceed the land boundary, avoiding the risk of creating unusable abandoned spaces in corner areas or encroaching on neighboring plots, thus achieving meticulous calculation and optimal utilization of every inch of land resources. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure and working environment of the system of the present invention; Figure 2 This is a geometric schematic diagram illustrating the core planning algorithm of this invention. Figure 3 This is a schematic diagram of the theoretical mesh generation and boundary trimming process of this invention; Figure 4 This is a flowchart of the overall system method of the present invention. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see the appendix Figure 1-4 This invention provides a positioning and guidance system for farmland planning. Physically, the system mainly consists of two parts: a high-precision data acquisition module serving as the on-site spatial data acquisition terminal, and a portable controller serving as the core for human-computer interaction and computation. The data processing and planning module, as well as the real-time positioning and guidance module, are encapsulated and run as core application software within the portable controller.

[0023] Specifically, the high-precision data acquisition module is shaped like a GNSS-RTK mobile station integrating a high-gain antenna and a multi-satellite, multi-frequency receiver motherboard. Its core function is to receive and process raw carrier phase observations from multiple global navigation satellite systems (such as GPS, GLONASS, BeiDou, and Galileo) in real time, providing high-precision three-dimensional spatial position information for the entire system.

[0024] The portable controller can be a rugged industrial-grade tablet or a large-screen smartphone, with an application specifically designed to implement the functions of this invention installed inside. This application not only provides users with a graphical user interface to display farmland boundaries, planning results, and navigation information, but also undertakes the computational tasks of core algorithms such as coordinate transformation and plot segmentation, which will be detailed later.

[0025] A stable and reliable data communication link is established between the high-precision data acquisition module and the portable controller carrying the core application. This link can be implemented through short-range wireless communication (such as Bluetooth technology) or through wired connection (such as USB or RS-232 serial port). The function of this link is to ensure that the high-frequency, high-precision coordinate data calculated by the GNSS-RTK rover can be transmitted to the portable controller without delay and loss, for use by the data processing and planning module and the real-time positioning and guidance module.

[0026] To ensure the system achieves and maintains centimeter-level positioning accuracy throughout the operation, the high-precision data acquisition module must receive and process differential correction data in real time. In this embodiment, the acquisition path for the differential correction data is flexible. One approach is for the operator to utilize the mobile communication function (e.g., 4G or 5G network) built into the portable controller to access the Continuously Operating Reference Stations (CORS) network on the Internet and subscribe to and receive real-time differential correction data streams via the standard Ntrip protocol.

[0027] Another approach is to set up a dedicated GNSS reference station in an open, unobstructed area near the farmland to be planned (usually within a 2-kilometer radius). After precisely calibrating its position, the reference station continuously compares its observation data with known coordinates, calculates differential corrections, and broadcasts this information to a high-precision data acquisition module (rover) via an ultra-high frequency (UHF) radio. Upon receiving this signal, the rover eliminates most common errors and calculates high-precision real-time coordinates. Both methods effectively mitigate the impact of major error sources such as ionospheric / tropospheric delay, satellite orbital errors, and satellite clock biases, thereby ensuring that all coordinates output by the system have extremely high absolute and relative accuracy.

[0028] In this embodiment, accurate mapping of farmland boundaries is the data foundation for all subsequent automated planning work, directly determining the accuracy of the final planning scheme. Therefore, this invention provides a detailed and flexible implementation method for high-precision mapping of farmland boundaries, aiming to accurately capture the actual geometric contours of the farmland to be planned through on-site surveys.

[0029] In practice, the operator carries an integrated device consisting of a high-precision data acquisition module and a portable controller, and walks to the starting point of the boundary of the farmland to be planned. After confirming that the GNSS-RTK rover has successfully obtained a "fixed solution" (i.e., achieved centimeter-level accuracy), the boundary acquisition function can be activated. The operator moves along the physical boundary line of the farmland (such as field ridges, ditch edges, or the line connecting plot boundary markers), and the system simultaneously records the key spatial location points on the operator's movement trajectory.

[0030] To adapt to the characteristics of different types of farmland boundaries, the application in this invention provides two main data acquisition modes for users to choose from based on the site conditions.

[0031] The first mode is "key point acquisition." This mode is particularly suitable for farmland with a relatively regular shape and boundaries composed of several straight line segments. The operator only needs to briefly pause at each obvious turning point of the farmland boundary and manually trigger a coordinate recording command by pressing a designated button on the touchscreen or a physical button on the device. Each trigger will accurately record the three-dimensional geodetic coordinates of the GNSS-RTK antenna phase center at the current moment. ,in Longitude Latitude The elevation is determined by the terrain. By recording all the turning points in sequence, a sparse point set that can accurately describe the outline of the farmland can be constructed.

[0032] The second mode is "continuous trajectory acquisition," which is more suitable for farmland with irregular curves or rich details. After activating this mode, the operator does not need to intervene manually; the system will automatically and continuously record boundary points according to a pre-set acquisition strategy. This strategy can be time-interval triggered, such as recording one point every second; or distance-interval triggered, such as recording one point every 0.5 meters. This automated recording method can meticulously depict every minute change in the farmland boundary in the form of a high-density point cloud, ensuring the fidelity of complex boundary contours.

[0033] Regardless of the acquisition mode used, all recorded coordinate points The data is collected in the order it was acquired, forming an ordered sequence of coordinate points. This sequence is stored in real-time in the non-volatile memory of the portable controller, typically in a specific file format (such as CSV or a custom binary format). This file serves not only as the raw digital archive of the farmland boundaries but also as direct input data for subsequent data processing and planning modules to perform coordinate transformations and geometric calculations. After data acquisition, the system automatically connects the first and last points to form a closed polygon, which is then visualized on the screen for the operator to perform initial checks and confirmations.

[0034] First, in order to perform accurate planar geometric calculations, the system must convert the geodetic coordinates of the farmland boundary points collected in the previous step, based on ellipsoidal models such as WGS-84, into geodetic coordinates. This is converted into two-dimensional rectangular coordinates that can be considered as a plane within a local area. This invention employs a standard geodetic projection method, such as the Gauss-Kruger projection, to achieve this conversion. During the projection process, the system automatically selects or recommends a central meridian based on the longitude of the area where the farmland to be planned is located, in order to minimize projection distortion. This is achieved through a projection function. Each geodetic coordinate point is uniquely mapped to a planar coordinate point. This results in a closed polygon representing the farmland boundary, formed by local plane coordinate points.

[0035] Next, the system will guide the user to input the key parameters necessary for community planning. On the application's user interface, the user needs to explicitly specify two core dimensions: the standard width of the community. and the standard length of the community In addition, users need to define the overall orientation of the planned community grid, i.e., the orientation angle of the planning baseline. To provide flexible and convenient operation, this invention designs two ways to define this direction angle: First, the user can select any two points on the farmland boundary outline displayed on the screen with their finger, and the system will immediately calculate the angle between the line connecting these two points and the due north direction of the local coordinate system, and automatically set it as the angle. Secondly, users can also directly enter a specific angle value in a numerical input box. For example, entering 0 degrees means that the edges of all cells will be parallel to the due north-south direction.

[0036] After obtaining all the necessary planning parameters, the system's core planning algorithm begins execution. The first step of the algorithm is to determine the direction angle of the given planning baseline. Construct a set of orthogonal unit basis vectors to define the mesh structure. Principal direction unit vectors. The normal unit vector along the planning baseline. Then it is perpendicular to it. The mathematical expressions for these two vectors are as follows:

[0037]

[0038] These two unit vectors act like two "rulers," defining the direction of subsequent mesh generation in the two principal directions.

[0039] The algorithm then proceeds to the generation phase of the theoretical mesh vertices. The system selects a starting point for computation. For example, you can select any of the vertices of the farmland boundary. The point with the smallest projection in a given direction is used as the starting point to optimize computational efficiency. Based on this starting point, the system generates a theoretically infinitely extending regular grid lattice covering the entire farmland area through a double loop using the following formula. Any theoretical grid vertex... The coordinates are given by the following formula:

[0040] In this formula, and These are integer indices, representing the "steps" from the starting point in the principal direction and normal direction, respectively; and These are the standard width and length of the cell input by the user, which are respectively related to the basis vectors. and Multiplication together determines the "step length" of each step.

[0041] Finally, and crucially, the generated theoretical mesh is trimmed to perfectly fit the irregular farmland boundaries. The system iterates through every vertex of the theoretical mesh. An inclusion test algorithm is applied to determine whether a vertex lies within or exactly on the boundary of a previously defined farmland polygon. An efficient and robust implementation uses the RayCasting Algorithm. This method starts from the vertex to be tested, draws a ray in any fixed direction (e.g., the positive X-axis), and then calculates the number of intersections between the ray and all edges of the polygon. If the number of intersections is odd, the point is inside the polygon; if it is even, it is outside. Through this precise filtering, all invalid vertices located outside the farmland are discarded, and only those located inside or on the boundary are retained. These vertices together constitute the final valid set of vertex coordinates for the plot. This coordinate set not only defines the precise location and shape of all standard and non-standard plots but also serves as the direct basis for the next step of on-site layout guidance.

[0042] In this embodiment, after the data processing and planning module successfully generates the coordinate set of all cell vertices, the system seamlessly switches to the real-time positioning and stakeout guidance function stage. The core task of this stage is to accurately reproduce the digital planning results into the physical world, that is, to guide on-site operators to accurately find and mark each planned cell vertex.

[0043] At the start of operation, the portable controller's screen loads and displays a map showing the planned farmland plots, including the farmland's boundary outlines and the vertices of all internal cells. The operator can freely zoom and pan the map, and select any cell vertex they wish to stake out. Once a vertex is selected, the system immediately extracts it from the cell vertex coordinate set and sets its local plane coordinates. Set as the current target point for lofting.

[0044] Meanwhile, the real-time positioning and guidance module continuously receives real-time location information from the high-precision data acquisition module. Each set of raw geodetic coordinates is immediately converted into local plane coordinates using the same projection parameters and methods as in the planning phase, thus obtaining the operator's precise current location. This process runs silently in the background at a high frequency (e.g., 5 times per second or higher), ensuring the real-time nature of the location information.

[0045] To provide operators with clear navigation guidance, the system calculates two core navigation parameters in real time based on the positions of the target point and the current point. The first parameter is the straight-line distance between the two. It visually reflects the distance between the operator and the target point. The formula for calculating this distance is as follows:

[0046] in, Let be the local plane coordinates of the target point, and This provides the real-time local planar coordinates of the current location. The calculated distance value will be prominently displayed in large font at a fixed position on the screen and will refresh in real time as the operator moves.

[0047] The second core navigation parameter is direction guidance. Knowing only the distance is insufficient for efficient target arrival; therefore, the system also needs to calculate the target point's direction relative to the current location, i.e., the target azimuth. This angle can be precisely obtained using the following arctangent function:

[0048] One intuitive way to provide guidance is to render a dynamic arrow on the portable controller's screen. The arrow's direction follows the target's azimuth in real time. The changes in the arrows mean that the operator only needs to adjust their direction of travel to align the equipment with the direction indicated by the arrows, thus ensuring that they are heading straight for the target point.

[0049] A more refined guidance method involves using a high-precision data acquisition module that can provide the user's instantaneous heading angle. When the user is moving in the direction indicated by the heading angle, the system can calculate the difference between the heading angle and the target azimuth angle, i.e., the turning angle. The system then converts this difference into clear instructions, such as displaying "Turn 15 degrees to the left" or "Move 0.8 meters to the right to align with the route" on the screen, thus providing users with more quantitative and precise adjustment guidelines.

[0050] As the operator follows the navigation instructions and approaches the target point, and the calculated straight-line distance... When the accuracy falls below a user-preset threshold (e.g., 5 cm depending on the job requirements), the system triggers a clear arrival notification mechanism. This mechanism can be multi-sensory; for example, the screen changes from blue (navigation status) to green (arrival status), while the device emits a continuous, high-frequency "beep" sound accompanied by regular vibration. This notification clearly informs the operator that their current position is within the allowable error range of the target point, allowing them to stop moving and perform physical marking operations such as stake driving, flag planting, or painting. After completing the layout of one point, the operator can select the next target point on the screen and repeat the above process until all planned points have been marked.

[0051] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A positioning guidance system for farmland area planning, characterized in that, include: The high-precision data acquisition module is used to collect and record the geodetic coordinates of multiple farmland boundary points of the farmland to be planned, so as to form the farmland boundary; The data processing and planning module, connected to the high-precision data acquisition module, is used to convert the geodetic coordinates of the farmland boundary points into local plane coordinates. Based on the planning parameters input by the user and combined with the farmland boundary, the algorithm generates one or more vertices of the plots, forming a set of plot vertex coordinates; The real-time positioning and guidance module is connected to the data processing and planning module and calls the real-time positioning function of the high-precision data acquisition module to: obtain the local plane coordinates of the user's current location on site; Once a user selects a target point from the set of vertex coordinates of the cell, navigation guidance information from the current location to the target point is calculated and provided.

2. The system according to claim 1, characterized in that, The high-precision data acquisition module is a real-time dynamic differential device for the Global Navigation Satellite System, and the geodetic coordinates are three-dimensional coordinates including longitude, latitude, and geodetic height.

3. The system according to claim 1, characterized in that, The specific method for coordinate transformation in the data processing and planning module is as follows: the geodetic coordinates are transformed into local plane coordinates using Gauss-Kruger projection or UTM projection.

4. The system according to claim 1, characterized in that, The planning parameters input by the user include: standard width of the cell, standard length of the cell, and direction angle of the planning baseline.

5. The system according to claim 4, characterized in that, The steps for generating cell vertices in the data processing and planning module include: According to the planning baseline direction angle Construct orthogonal unit basis vectors and ; Select the starting point for calculation And through the formula ； Generate theoretical mesh vertices, where The standard width of the cell is... The standard length of the cell is... and Integer index.

6. The system according to claim 5, characterized in that, The data processing and planning module further extracts the vertices located inside or on the boundaries of the polygon by performing Boolean operations on the generated theoretical grid vertices and the polygon formed by the farmland boundary, thus forming the final set of vertex coordinates of the plot.

7. The system according to claim 1, characterized in that, The navigation guidance information provided by the real-time positioning and guidance module includes the straight-line distance from the current location to the target point. The calculation formula is as follows: ； in, Let be the local plane coordinates of the target point. The coordinates of the current location are the local plane coordinates.

8. The system according to claim 1 or 7, characterized in that, The navigation guidance information also includes a target azimuth angle, used to indicate the direction of the target point relative to the current position.

9. The system according to claim 4, characterized in that, The orientation angle of the planning baseline is automatically determined by the user by selecting any two points on the farmland boundary, or it can be specified by the user by directly inputting the angle value.

10. The system according to claim 1, characterized in that, The real-time positioning and guidance module sends an arrival prompt to the user when the straight-line distance between the current location and the target point is less than a preset accuracy threshold.

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