A method for planning vehicle U-turn routes
By calculating road space width and planning U-turn routes of various shapes, the problem of poor adaptability in traditional methods is solved, and optimized path planning under different intersection relationships is achieved, avoiding collisions and wasted space.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHENGZHOU YUTONG BUS CO LTD
- Filing Date
- 2021-12-10
- Publication Date
- 2026-05-26
AI Technical Summary
Traditional vehicle U-turn route planning methods only consider parallel intersections and cannot adapt to complex traffic environments with non-parallel intersections, resulting in poor adaptability of route planning.
By acquiring intersection information and vehicle attributes, the relationship between intersections is determined, the road space width is calculated, and U-turn paths in the shape of arcs, bows, pears, or semi-pears are planned according to different situations. The paths are then optimized by combining obstacle information.
It enables path planning under different intersection relationships, improves the adaptability of U-turn paths, avoids collisions with obstacles, and optimizes space utilization.
Smart Images
Figure CN116252799B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for planning vehicle U-turn routes, belonging to the field of intelligent driving technology. Background Technology
[0002] For autonomous vehicles, U-turn path planning at intersections with complex traffic flow needs to achieve two basic functions: First, accurate point-to-point path planning (the orientation of the planning start and end points meets the requirements); Second, within a limited operating area, the planned trajectory should occupy as little space as possible and avoid collisions with surrounding obstacles.
[0003] Traditional U-turn route planning only considers the case where the entrance and exit are parallel, and then makes a route plan with the minimum turning radius based on the road width. The route plan can be planned in various shapes such as semi-circular turns, bow turns, pear turns, and fishtail turns. However, with the increasing complexity of road traffic, the phenomenon of entrances and exits not being parallel often occurs. Therefore, traditional U-turn route planning cannot meet the needs of all roads and has poor adaptability. Summary of the Invention
[0004] The purpose of this application is to provide a vehicle U-turn route planning method to solve the problem that existing planning methods only consider parallel cases, resulting in poor adaptability of the planned routes.
[0005] To achieve the above objectives, this application proposes a technical solution for a vehicle U-turn path planning method, comprising the following steps:
[0006] 1) Obtain road information for entrances and exits, maximum speed limit for U-turns, lateral acceleration for U-turns, and minimum turning radius of vehicles; road information includes the direction of road extension and the location of the road;
[0007] 2) Determine the minimum turning radius based on the maximum speed limit for U-turns, the lateral acceleration for U-turns, and the vehicle's minimum turning radius;
[0008] 3) Determine the pose of the starting point at the entrance and the pose of the ending point at the exit. The pose includes position and heading angle. The heading angle of the starting point is the same as the extension direction of the entrance and the heading angle of the ending point is the same as the extension direction of the exit.
[0009] 4) Determine the relationship between the entrance and exit based on the road information at the entrance and exit, and then determine the road space width for the U-turn:
[0010] If the entrance and exit are parallel, the vertical width of the two roads is the same as the road space width when making a U-turn.
[0011] If the entrance and exit intersect at an acute angle, then draw circles tangent to the entrance and exit roads, respectively, with the starting point and the ending point as the points of tangency. Take the radius of the smaller circle as the width of the road space when making a U-turn. The acute angle intersection occurs when the distance between the entrance and exit decreases along the extension direction of the entrance.
[0012] If the entrance and exit intersect at an obtuse angle, draw circles tangent to the entrance and exit roads, respectively, with the starting and ending points as the points of tangency. Take the radius of the larger circle as the width of the road space when making a U-turn. An obtuse angle means that the distance between the entrance and exit increases along the extension direction of the entrance.
[0013] 5) Determine the shape of the planned path trajectory based on the relationship between the road space width during a U-turn and the minimum turning radius:
[0014] If half of the road space width at the time of the U-turn is greater than or equal to the minimum turning radius, then the U-turn path should be planned in an arc or bow shape.
[0015] If half of the road space width at the time of the U-turn is less than the minimum turning radius, then the U-turn path should be planned according to a pear shape or a semi-pear shape.
[0016] The beneficial effects of the vehicle U-turn path planning method of the present invention are as follows: The present invention determines the road space width for U-turns under the conditions of parallel, acute-angle, and obtuse-angle intersections of the entrance and exit. Then, based on the relationship between the road space width and the minimum turning radius under different conditions, the shape of the planned U-turn path is determined, thus completing the U-turn path planning. The present invention can realize U-turn path planning under conditions of parallel, acute-angle, and obtuse-angle intersections of entrances and exits, improving the adaptability of U-turn path planning at different intersections.
[0017] Furthermore, when planning a U-turn path in an arc shape, if the entrance and exit are parallel, the turning radius is half the width of the road space when making the U-turn, and the arc-shaped U-turn path is obtained based on the poses of the starting and ending points and the turning radius; if the entrance and exit intersect at an acute angle or an obtuse angle, the turning radius is the width of the road space when making the U-turn, and the arc-shaped U-turn path is obtained based on the poses of the starting and ending points and the turning radius.
[0018] Furthermore, when planning a U-turn path according to an arc shape, the turning radius changes from the minimum turning radius to the maximum turning radius, forming an arc-shaped U-turn path cluster. The process of determining a specific arc-shaped U-turn path within the arc-shaped U-turn path cluster is as follows:
[0019] Using the starting point and the ending point as tangent points respectively, draw a starting circle tangent to the entrance road and an ending circle tangent to the exit road according to the turning radius. Draw tangent lines to the starting circle and the ending circle. The starting circle, tangent lines, and ending circle form an arc-shaped U-turn path.
[0020] Furthermore, among the cluster of bow-shaped U-turn paths, the bow-shaped U-turn path with the smallest space occupation is identified as the optimal bow-shaped U-turn path.
[0021] Furthermore, obstacle information is obtained, and the bow-shaped U-turn path with no obstacles and the smallest space occupies is selected as the optimal bow-shaped U-turn path from the bow-shaped U-turn path cluster.
[0022] Furthermore, when planning U-turn paths according to a pear shape or semi-pear shape, the process for determining the pear-shaped or semi-pear-shaped U-turn path is as follows:
[0023] With the starting point as the tangent point and the minimum turning radius as the first radius, construct a right-turn circle tangent to the entrance road;
[0024] Draw a left-turning circle tangent to the right-turning circle according to the second radius. The angle between the point of tangency of the right-turning circle and the left-turning circle and the arc corresponding to the starting point on the right-turning circle is less than the set angle.
[0025] The second radius changes from the minimum turning radius to the maximum turning radius, forming a cluster of pear-shaped and / or semi-pear-shaped U-turn paths:
[0026] During the process of increasing the second radius, if the left-turn circle corresponding to a certain second radius is tangent to the exit road, then a straight line is drawn from the point of tangency between the left-turn circle and the exit road to the endpoint, and the right-turn circle, left-turn circle, and straight line form a half-pear-shaped U-turn path; if the left-turn circle corresponding to a certain second radius intersects with the exit road, then a return circle tangent to the exit road is drawn with the endpoint as the point of tangency and the minimum turning radius as the third radius, and the right-turn circle, left-turn circle, and return circle form a pear-shaped U-turn path.
[0027] Furthermore, among the pear-shaped and / or semi-pear-shaped U-turn path clusters, the U-turn path with the smallest space occupation is identified as the optimal U-turn path.
[0028] Furthermore, obstacle information is also obtained, and among the pear-shaped and / or semi-pear-shaped U-turn path clusters, the U-turn path with no obstacles and the smallest space occupation is identified as the optimal U-turn path.
[0029] Furthermore, if all paths in the bow-shaped U-turn path cluster contain obstacles, the starting point is shifted along the heading angle direction of the starting point, and the bow-shaped U-turn path cluster is replanned.
[0030] Furthermore, if all paths in the pear-shaped and / or semi-pear-shaped U-turn path cluster contain obstacles, the starting point is shifted along the heading angle direction of the starting point, and the pear-shaped and / or semi-pear-shaped U-turn path cluster is replanned. Attached Figure Description
[0031] Figure 1 This is a flowchart of the vehicle U-turn path planning method of the present invention;
[0032] Figure 2a This is a schematic diagram showing the road space width when making a U-turn, assuming the entrance and exit are parallel according to the present invention.
[0033] Figure 2b This is a schematic diagram showing the road space width when making a U-turn at an acute angle where the entrance and exit of the road intersect.
[0034] Figure 2c This is a schematic diagram showing the road space width when making a U-turn at an obtuse angle where the entrance and exit of the road intersect.
[0035] Figure 3a This is a schematic diagram of the arc-shaped U-turn path cluster when the entrance and exit are parallel according to the present invention;
[0036] Figure 3b This is a schematic diagram of the arc-shaped U-turn path cluster when the entrance and exit of the present invention intersect at an acute angle;
[0037] Figure 4a This is a schematic diagram of the arc-shaped U-turn path when the entrance and exit of the present invention are parallel;
[0038] Figure 4b This is a schematic diagram of the arc-shaped U-turn path when the intersection and exit of the road intersect at an acute angle according to the present invention;
[0039] Figure 5a This is a schematic diagram of the semi-pear-shaped U-turn path when the intersection and exit are parallel according to the present invention;
[0040] Figure 5b This is a schematic diagram of the semi-pear-shaped U-turn path when the entrance and exit of the present invention intersect at an obtuse angle;
[0041] Figure 6 This is a schematic diagram of the pear-shaped U-turn path when the entrance and exit are parallel according to the present invention;
[0042] Figure 7a This is a schematic diagram of the pear-shaped U-turn path cluster with increased second radius according to the present invention;
[0043] Figure 7b This is a schematic diagram of the pear-shaped U-turn path cluster of the present invention, which changes the set angle and increases the second radius;
[0044] Figure 8 This is a flowchart of the screening trajectory of the present invention. Detailed Implementation
[0045] Example of a vehicle U-turn route planning method:
[0046] The main concept of this invention is to address the problem of poor adaptability in U-turn path planning when only considering the parallelism of the entrance and exit. This invention determines the relationship between the entrance and exit, and then calculates the road space width for U-turns under various conditions based on whether the entrance and exit are parallel, intersecting at an acute angle, or intersecting at an obtuse angle. Based on the road space width for U-turns and the minimum turning radius, it determines arc-shaped, bow-shaped, pear-shaped, or semi-pear-shaped U-turn paths.
[0047] Specifically, the vehicle U-turn path planning method is as follows: Figure 1 As shown, it includes the following steps:
[0048] 1) Obtain road information at the entrance and exit, maximum speed limit for U-turns, lateral acceleration for U-turns, minimum turning radius of the vehicle, vehicle length, and obstacle information; and determine the pose of the starting point at the entrance and the pose of the ending point at the exit.
[0049] In this step, the road information includes the direction of road extension and the location of the road, which can be obtained from the map. That is, the road information for the entrance is the straight line L1, and the equation of the straight line L1 is: A1*x+B1*y+C1=0; the road information for the exit is the straight line L2, and the equation of the straight line L2 is: A2*x+B2*y+C2=0.
[0050] The maximum speed limit for U-turns, V_max, and the lateral acceleration for U-turns, a, are fixed values specified for road driving.
[0051] Minimum turning radius of vehicle R_min 车 The vehicle length, car_length, is a vehicle attribute value, and different vehicles have different attribute values.
[0052] Obstacle information (OBS) is obtained from the map and the vehicle's perception module. Here, obstacle information (OBS) refers to static obstacle information around the vehicle, such as curbs.
[0053] Determine the pose (x1, y1, phi_1) of the starting point A at the entrance and the pose (x2, y2, phi_2) of the ending point B at the exit; (x1, y1) is the coordinate position of the starting point, and phi_1 is the heading angle of the starting point; (x2, y2) is the coordinate position of the ending point, and phi_2 is the heading angle of the ending point; the heading angle of the starting point is the same as the extension direction of the entrance, and the heading angle of the ending point is the same as the extension direction of the exit.
[0054] 2) Determine the minimum turning radius and the maximum turning radius.
[0055] The minimum turning radius is based on the maximum speed limit for U-turns (V_max), the lateral acceleration for U-turns (a), and the vehicle's minimum turning radius (R_min). 车 Therefore, when turning at an intersection, in order to prevent skidding, Combined with the vehicle's minimum turning radius R_min 车 The minimum turning radius is obtained as follows:
[0056] R_min = max(Rv, R_min) 车 );
[0057] Where R_min is the minimum turning radius; V_max is the maximum speed limit for a U-turn; a is the lateral acceleration for a U-turn; R_min 车 This is the vehicle's minimum turning radius.
[0058] The maximum turning radius R_max is generally directly equal to the vehicle length car_length; the reason is:
[0059] When the steering wheel is turned at a fixed angle and a U-turn is made in one go, the trajectory is the easiest to track. Therefore, when the intersection space is large, it is appropriate to consider using a large arc trajectory with a turning radius R > R_min to pass through in one go. Considering that the intersection should occupy as little space as possible, we define the maximum turning radius R_max = k * car_length, and in general, k = 1.
[0060] 3) Determine the relationship between the entrance and exit based on the road information of the entrance and exit, and then determine the road space width (road_width) when making a U-turn.
[0061] From the equations of the approach road line L1 (A1*x+B1*y+C1=0) and the exit road line L2 (A2*x+B2*y+C2=0) in step 1), we can obtain the intersection relationship between the approach and exit roads.
[0062] like Figure 2a As shown, if the entrance and exit are parallel, that is, straight lines L1 and L2 are parallel, then A1 = A2 = A, B1 = B2 = B, and the vertical width of the two roads is the road space width when making a U-turn (road_width).
[0063]
[0064] like Figure 2bAs shown, if the entrance and exit intersect at an acute angle (an acute angle means that the distance between the entrance and exit decreases along the extension direction of the entrance), then, using point A as the tangent point, draw a circle with radius r1 that is tangent to both lines L1 and L2 simultaneously. Similarly, using point B as the tangent point, draw a circle with radius r2 that is tangent to both lines L1 and L2 simultaneously. The road width (road_width) for the U-turn is:
[0065] road_width = min(r1, r2);
[0066] like Figure 2c As shown, if the entrance and exit intersect at an obtuse angle (an obtuse angle means that the distance between the entrance and exit increases along the extension direction of the entrance), then, using point A as the tangent point, draw a circle with radius r1 that is tangent to both lines L1 and L2 simultaneously. Similarly, using point B as the tangent point, draw a circle with radius r2 that is tangent to both lines L1 and L2 simultaneously. The road width (road_width) for the U-turn is:
[0067] road_width = max(r1, r2).
[0068] 4) Determine the width of the road space when making a U-turn, and then determine the shape of the generated path trajectory based on the width of the road space when making a U-turn, and generate a U-turn path cluster according to the corresponding path trajectory shape.
[0069] In this step, if half of the road space width when making a U-turn (road_width / 2) is greater than or equal to the minimum turning radius (R_min), then the U-turn path is planned in either an arc or an arc shape.
[0070] If half of the road width (road_width / 2) at the time of the U-turn is less than the minimum turning radius (R_min), then the U-turn path is planned according to a pear shape or a semi-pear shape.
[0071] Specifically, the case where road_width / 2 ≥ R_min can be further divided into the following two cases:
[0072] The first scenario: When road_width / 2 > R_max, it indicates that the road space width is relatively large when making a U-turn. Generally, an arc-shaped U-turn path is planned, such as... Figure 3a , Figure 3b As shown ( Figure 3a For the case where lines L1 and L2 are parallel, Figure 3b(When lines L1 and L2 intersect at an acute angle), when planning a U-turn path according to an arc shape, the turning radius R changes from the minimum turning radius to the maximum turning radius, forming an arc-shaped U-turn path cluster. An arc-shaped U-turn path includes two circular arc segments and a straight line segment between the two arcs. The two circular arc segments include the arc of the starting circle tangent to the approach road and the arc of the ending circle tangent to the exit road. The straight line segment is a tangent line simultaneously tangent to both circles. The process of determining a specific arc-shaped U-turn path within the arc-shaped U-turn path cluster is as follows:
[0073] Using the starting point A and the ending point B as tangent points respectively, draw a starting circle tangent to the entrance road and an ending circle tangent to the exit road according to the turning radius R. Draw the tangent lines of the starting circle and the ending circle. The starting circle, the tangent lines, and the ending circle form an arc-shaped U-turn path.
[0074] The second scenario: When R_min <= road_Ridth / 2 <= R_max, it indicates that the turning space is appropriate. Considering both the difficulty of tracking and the space occupied by the trajectory, two line shapes can be used for planning: circular arc trajectory and bow-shaped trajectory. When planning the turning path according to the circular arc shape, as follows... Figure 4a As shown, if the entrance and exit are parallel, then the turning radius R (R = road_width / 2) is half the width of the road space when making a U-turn. Based on the poses of the starting and ending points and the turning radius, an arc-shaped U-turn path is obtained. Specifically, a circle is drawn with the starting point as the tangent point and half the width of the road space when making a U-turn as the turning radius R, tangent to both the entrance and exit roads. The positional relationship between the tangent point of this circle and the exit road and the ending point is determined.
[0075] If the point of tangency between the circle and the road at the exit coincides with the endpoint, then the arc of the circle is the arc-shaped U-turn path.
[0076] If the point of tangency between the circle and the road at the exit is above the endpoint, then draw a straight line from the point of tangency to the endpoint. The arc segment plus the straight line segment forms an arc-shaped U-turn path.
[0077] If the point of tangency between the circle and the exit road is below the endpoint, or if the circle cannot be tangent to the exit road (i.e., a trajectory cannot be formed), then adjust the position of the starting point (move point A up or down), and redraw a circle tangent to the entrance and exit roads with the starting point as the point of tangency and half the width of the road space when making a U-turn as the turning radius R.
[0078] like Figure 4bAs shown, if the entrance and exit intersect at an acute angle or an obtuse angle, the turning radius R (R = r1 or R = r2) is taken as the width of the road space at the time of the U-turn. Based on the poses of the starting and ending points and the turning radius, an arc-shaped U-turn path is obtained. Specifically, a circle tangent to the entrance and exit roads is drawn with the starting point as the tangent point and the turning radius R as the width of the road space at the time of the U-turn. The positional relationship between the tangent point of this circle and the exit road and the ending point is determined.
[0079] If the point of tangency between the circle and the road at the exit coincides with the endpoint, then the arc of the circle is the arc-shaped U-turn path.
[0080] If the point of tangency between the circle and the road at the exit is above the endpoint, then draw a straight line from the point of tangency to the endpoint. The arc segment plus the straight line segment forms an arc-shaped U-turn path.
[0081] If the point of tangency between the circle and the exit road is below the endpoint, or if the circle cannot be tangent to the exit road, then adjust the position of the starting point, and draw a circle tangent to both the entrance and exit roads, with the starting point as the point of tangency and the width of the road space at the time of the U-turn as the turning radius R.
[0082] In the second scenario, the arc shape is easy to track, and generally the endpoint is below the starting point. It's rare for the circle and the exit road to be tangent at the endpoint, or for the circle and the exit road to not be tangent. Therefore, an arc-shaped U-turn path can usually be successfully planned in one attempt. However, if there are obstacles on the planned arc-shaped U-turn path, an bow-shaped path cluster is used for planning. While bow-shaped planning is preferred in the first scenario, arc-shaped planning can also be used; this invention does not impose any limitations on this.
[0083] When road_width / 2 < R_min, it indicates that the U-turn space is relatively narrow, and a one-time arc-shaped U-turn trajectory and bow-shaped U-turn path cluster cannot be formed. In this case, the U-turn path is planned according to a pear shape or a semi-pear shape.
[0084] When planning a U-turn path based on a pear-shaped or semi-pear-shaped pattern, the process for determining the pear-shaped or semi-pear-shaped U-turn path is as follows:
[0085] With the starting point A as the tangent point and the minimum turning radius R_min as the first radius R1, construct a right-turn circle tangent to the entrance road (see attached diagram). Figure 1 (circle S1 in the middle);
[0086] Draw a left-turning circle tangent to the right-turning circle using the second radius R2 (see attached diagram). Figure 1In circle S2), the angle between the tangent point of the right turn circle and the left turn circle and the arc corresponding to the starting point on the right turn circle is less than the set angle (0 < set angle < 90°). (In order to find the optimal turning trajectory, the angle between the tangent point of the right turn circle and the left turn circle and the arc corresponding to the starting point on the right turn circle can be changed).
[0087] The second radius R2 changes from the minimum turning radius to the maximum turning radius (i.e., R2 belongs to [R_min, R_max]), forming a cluster of U-turn paths including pear-shaped and / or semi-pear-shaped paths. During the increase of the second radius R2, the left-turn circle and the straight line L2 may be in a state of separation, tangency, or intersection:
[0088] If the left-turn circle corresponding to a certain second radius R2 is separate from the exit road, a U-turn trajectory cannot be formed, and the second radius R2 is further increased;
[0089] like Figure 5a , Figure 5b As shown ( Figure 5a Lines L1 and L2 are parallel. Figure 5b If lines L1 and L2 intersect at an obtuse angle, and the left-turn circle corresponding to a certain second radius R2 is tangent to the exit road, then determine the positional relationship between the point of tangency of the left-turn circle and the exit road and the endpoint. If the point of tangency is above the endpoint, draw a straight line from the point of tangency of the left-turn circle and the exit road to the endpoint. The arc segments of the right-turn circle and the left-turn circle, along with the straight line, form a semi-pear-shaped U-turn path. If the point of tangency is below the endpoint, then adjust the position of the starting point and replan.
[0090] like Figure 6 As shown, if a left-turn circle corresponding to a certain second radius R2 intersects the exit road, then a return circle tangent to the exit road is constructed with the endpoint as the tangent point and the minimum turning radius as the third radius R3 (see attached diagram). Figure 1 The circular arc segments of the circle S3 in the middle, the right-turn circle, the left-turn circle, and the return circle form a pear-shaped U-turn path.
[0091] The final form is as follows Figure 7a , Figure 7b As shown ( Figure 7a The path cluster formed by increasing the second radius R2, Figure 7b The pear-shaped and / or semi-pear-shaped U-turn path clusters (formed by changing the setting angle and increasing the second radius R2) include the following three cases:
[0092] In the first case, as the second radius R2 increases, until R2 increases to R_max, the left-turning circle is tangent to the straight line L2, at which point a semi-pear-shaped U-turn path cluster is formed;
[0093] In the second case, the process of increasing the second radius R2 includes the state where the left-turning circle and the straight line L2 go from being tangent to intersecting, at which point a cluster of turning paths from a half-pear shape to a pear shape is formed.
[0094] In the third scenario, based on the settings, only pear-shaped turning trajectories are selected to form a pear-shaped turning path cluster in the second scenario.
[0095] 5) Filtering trajectories (i.e.) Figure 1 (Trajectory post-processing in the process).
[0096] The screening process is as follows Figure 8 As shown, collision detection is performed on the generated U-turn path cluster to find the U-turn path cluster without obstacles. Among the U-turn path clusters without obstacles, the U-turn path with the smallest space is selected as the optimal U-turn path.
[0097] If all paths in various U-turn path clusters contain obstacles, then the starting point A is shifted along the heading angle of the starting point or the ending point B is shifted along the heading angle of the ending point (that is, point A moves up and point B moves down), and various U-turn path clusters are replanned until a usable trajectory is available.
[0098] This invention can realize U-turn path planning in cases where the entrance and exit are parallel, intersecting at acute angles and obtuse angles, thus improving the adaptability of U-turn path planning at different intersections.
Claims
1. A method for planning a vehicle U-turn path, characterized in that, Includes the following steps: 1) Obtain road information for entrances and exits, maximum speed limit for U-turns, lateral acceleration for U-turns, and minimum turning radius of vehicles; road information includes the direction of road extension and the location of the road; 2) Determine the minimum turning radius based on the maximum speed limit for U-turns, the lateral acceleration for U-turns, and the vehicle's minimum turning radius; 3) Determine the pose of the starting point at the entrance and the pose of the ending point at the exit. The pose includes position and heading angle. The heading angle of the starting point is the same as the extension direction of the entrance and the heading angle of the ending point is the same as the extension direction of the exit. 4) Determine the relationship between the entrance and exit based on the road information at the entrance and exit, and then determine the road space width for the U-turn: If the entrance and exit are parallel, the vertical width of the two roads is the same as the road space width when making a U-turn. If the entrance and exit intersect at an acute angle, then draw circles tangent to the entrance and exit roads, respectively, with the starting point and the ending point as the points of tangency. Take the radius of the smaller circle as the width of the road space when making a U-turn. The acute angle intersection occurs when the distance between the entrance and exit decreases along the extension direction of the entrance. If the entrance and exit intersect at an obtuse angle, draw circles tangent to the entrance and exit roads, respectively, with the starting and ending points as the points of tangency. Take the radius of the larger circle as the width of the road space when making a U-turn. An obtuse angle means that the distance between the entrance and exit increases along the extension direction of the entrance. 5) Determine the shape of the planned path trajectory based on the relationship between the road space width during a U-turn and the minimum turning radius: If half of the road space width at the time of the U-turn is greater than or equal to the minimum turning radius, then the U-turn path should be planned in an arc or bow shape. If half of the road space width at the time of the U-turn is less than the minimum turning radius, then the U-turn path should be planned according to a pear shape or a semi-pear shape.
2. The vehicle U-turn path planning method according to claim 1, characterized in that, When planning a U-turn path in an arc shape, if the entrance and exit are parallel, the turning radius is half the width of the road space at the time of the U-turn, and the arc-shaped U-turn path is obtained based on the poses of the starting and ending points and the turning radius. If the entrance and exit intersect at an acute angle or an obtuse angle, the turning radius is the width of the road space at the time of the U-turn, and the arc-shaped U-turn path is obtained based on the poses of the starting and ending points and the turning radius.
3. The vehicle U-turn path planning method according to claim 1, characterized in that, When planning a U-turn path in an arc shape, the turning radius changes from the minimum turning radius to the maximum turning radius, forming an arc-shaped U-turn path cluster. The process of determining a specific arc-shaped U-turn path within this cluster is as follows: Using the starting point and the ending point as tangent points respectively, draw a starting circle tangent to the entrance road and an ending circle tangent to the exit road according to the turning radius. Draw tangent lines to the starting circle and the ending circle. The starting circle, tangent lines, and ending circle form an arc-shaped U-turn path.
4. The vehicle U-turn path planning method according to claim 3, characterized in that, Among the cluster of bow-shaped U-turn paths, the bow-shaped U-turn path with the smallest space occupation is selected as the optimal bow-shaped U-turn path.
5. The vehicle U-turn path planning method according to claim 3, characterized in that, It also acquires obstacle information, and in the cluster of bow-shaped U-turn paths, finds the bow-shaped U-turn path with no obstacles and the smallest space occupation as the optimal bow-shaped U-turn path.
6. The vehicle U-turn path planning method according to claim 1, characterized in that, When planning a U-turn path based on a pear-shaped or semi-pear-shaped pattern, the process for determining the pear-shaped or semi-pear-shaped U-turn path is as follows: With the starting point as the tangent point and the minimum turning radius as the first radius, construct a right-turn circle tangent to the entrance road; Draw a left-turning circle tangent to the right-turning circle according to the second radius. The angle between the point of tangency of the right-turning circle and the left-turning circle and the arc corresponding to the starting point on the right-turning circle is less than the set angle. The second radius changes from the minimum turning radius to the maximum turning radius, forming a cluster of pear-shaped and / or semi-pear-shaped U-turn paths: During the process of increasing the second radius, if the left-turn circle corresponding to a certain second radius is tangent to the exit road, then a straight line is drawn from the point of tangency between the left-turn circle and the exit road to the endpoint, and the right-turn circle, left-turn circle, and straight line form a half-pear-shaped U-turn path; if the left-turn circle corresponding to a certain second radius intersects with the exit road, then a return circle tangent to the exit road is drawn with the endpoint as the point of tangency and the minimum turning radius as the third radius, and the right-turn circle, left-turn circle, and return circle form a pear-shaped U-turn path.
7. The vehicle U-turn path planning method according to claim 6, characterized in that, Among the pear-shaped and / or semi-pear-shaped U-turn path clusters, the U-turn path with the smallest space occupies is identified as the optimal U-turn path.
8. The vehicle U-turn path planning method according to claim 6, characterized in that, It also acquires obstacle information, and in the pear-shaped and / or semi-pear-shaped U-turn path clusters, finds the U-turn path with no obstacles and the smallest space occupation as the optimal U-turn path.
9. The vehicle U-turn path planning method according to claim 5, characterized in that, If all paths in the bow-shaped U-turn path cluster contain obstacles, then the starting point is shifted along the heading angle of the starting point, and the bow-shaped U-turn path cluster is replanned.
10. The vehicle U-turn path planning method according to claim 8, characterized in that, If all paths in the pear-shaped and / or semi-pear-shaped U-turn path cluster contain obstacles, then the starting point is shifted along the heading angle direction of the starting point, and the pear-shaped and / or semi-pear-shaped U-turn path cluster is replanned.