A method for measuring the minimum turning radius of a car

Abstract

The present invention discloses a method for measuring the minimum turning radius of an automobile. Scanning positioning points are arranged on the front of the automobile, the front bumper and the transition plate respectively, and each scanning positioning point is collected to obtain a horizontal plane 3D point cloud image and a 3D point cloud image without a corner; the steering wheel is controlled to turn left to the limit angle, and two distances are advanced in sequence to obtain two 3D point cloud images of left turn; the steering wheel is controlled to turn right to the limit angle, and two distances are advanced in sequence to obtain two 3D point cloud images of right turn; the horizontal plane 3D point cloud image, the 3D point cloud image without a corner, the 3D point cloud image of left turn and the 3D point cloud image of right turn are processed to obtain a left track circle and a right track circle, and the average value of the radius of the left track circle and the right track circle is taken as the turning radius of the automobile. The present invention can quickly, effectively and accurately obtain the outermost contour line of the turn without the aid of other tools or equipment, solves the problem that the outermost convex point of the turn cannot be determined, and can quickly and accurately obtain the minimum turning radius through circumscribed circle fitting with high precision.

Description

Technical Field

[0001] The invention belongs to the technical field of automobiles, and in particular relates to a method for measuring a minimum turning radius of an automobile. Background Art

[0002] The minimum turning radius is an important parameter for measuring the passability of a car. It represents the car's ability to pass through narrow and curved areas. The smaller the minimum turning radius, the better the car's maneuverability. According to the different measurement boundaries and application scenarios, there are two corresponding radii.

[0003] The minimum turning radius (size code D101) refers to the radius of the circle that the center plane of the outer steering wheel rolls on the supporting plane when the vehicle is turning at the lowest stable speed when the steering wheel is turned to the extreme position; this radius measures the vehicle's passability on general roads.

[0004] The minimum turning radius (size code D102) refers to the radius of the trajectory circle that the projection of the outermost convex point of the vehicle's outer surface on the supporting plane rolls over when the steering wheel is turned to the extreme position and the vehicle is turning at the lowest stable speed. This radius measures the vehicle's passability in spaces with walls, such as underground garages, tunnels, alleys, etc.

[0005] Patent CN107655384A discloses a method for measuring the minimum turning radius of an automobile and a steering center marking system, which controls the steering wheel of an automobile to turn to a maximum angle in one direction; calibrates the first steering center of the automobile through the steering center marking system; measures the distance L from the first steering center of the automobile to the steering wheel of the automobile; controls the steering wheel of the automobile to turn in another direction and repeats the above steps to measure the second steering center of the automobile, and measures the distance L1 from the second steering center of the automobile to the steering wheel of the automobile; compares the sizes of L1 and L; and estimates whether the minimum turning radius of the automobile meets the design requirements based on the smaller of the two, the front wheelbase of the automobile and the set value of the minimum turning radius of the automobile.

[0006] This patent estimates the minimum turning radius of a vehicle through the distance from the first steering center to the steering wheel of the vehicle, the distance from the second steering center to the steering wheel of the vehicle, the front wheel spacing of the vehicle and the minimum turning radius setting value of the vehicle. This method requires measuring multiple values, and the final value obtained is also an estimated value, and the result may not be accurate. At the same time, this method cannot be used to measure the minimum turning radius (size code D102).

[0007] Patent CN113074965A discloses a static measurement method for the minimum turning radius of a vehicle, wherein a laser displacement sensor is used to measure the distance from the left and right edges of the measuring front wheel, and the turning angle of the front wheel of the measuring vehicle relative to the laser position sensor is calculated in the initial state; the steering wheel of the measuring vehicle is turned to the extreme position, and the laser displacement sensor is used to measure the distance from the left and right edges of the front wheel of the measuring vehicle; the maximum deflection angle of the front wheel of the measuring vehicle relative to the laser position sensor is calculated; the corrected maximum deflection angle of the front wheel relative to the laser displacement sensor is calculated; and the minimum turning radius of the measuring vehicle for right turn and left turn is calculated respectively according to the actual maximum deflection angle of the front wheel. When measuring the angle in this patent, the left and right edge positions of the front wheel can only be visually observed and cannot be accurately located; the formula and steps for angle calculation are complex and have large errors; the minimum turning radius is also a calculated value, and the wheelbase L is required, but there is no accurate measurement method for the wheelbase, and this method cannot be used to measure the minimum turning radius (size code D102).

[0008] Patent CN108845569A discloses a semi-automatic point cloud method for generating horizontal curved driving lanes in a three-dimensional high-definition road map, the steps are: S1, dividing the original point cloud data into several data blocks; S2, gridding the contours in each data block, and selecting the main point in each grid unit; S3, extracting curb points from the original point cloud data; S4, fitting the extracted curb points into two smooth roadsides to extract road surface points; S5, performing IDW interpolation on the road surface points to generate a GRF intensity feature image; S6, extracting and denoising road markings; S7, classifying discrete road marking points; S8, fitting the clustered curve road markings to obtain the driving lanes of the horizontal curved section; S9, adjusting the driving lanes according to existing knowledge. This method cannot be used to measure the minimum turning radius (size code D102).

[0009] The existing technologies all measure the minimum turning radius (size code D101), and all have certain limitations. Currently, there is no measurement of the minimum turning radius (size code D102). Summary of the invention

[0010] The purpose of the present invention is to solve the deficiencies of the above-mentioned background technology and to provide a convenient, efficient and accurate method for measuring the minimum turning radius (size code D102) of an automobile.

[0011] The technical solution adopted by the present invention is: a method for measuring the minimum turning radius of an automobile, wherein scanning positioning points are arranged on the front of the automobile, the front bumper and the transition plate respectively, and the coordinates of each scanning positioning point are collected and processed to obtain a horizontal plane 3D point cloud image and a 3D point cloud image of the front bumper without turning corners;

[0012] Control the steering wheel to turn left to the limit angle, move forward two distances in sequence, collect the scanning positioning point coordinates of the front bumper at two positions respectively, and process them to obtain two left-turn 3D point cloud images of the front bumper;

[0013] Control the steering wheel to turn right to the limit angle, move forward two distances in sequence, collect the scanning positioning point coordinates of the front bumper at two positions respectively, and process them to obtain two right-turn 3D point cloud images of the front bumper;

[0014] The horizontal plane 3D point cloud image, the 3D point cloud image without turning corners, the left-turn 3D point cloud image and the right-turn 3D point cloud image are processed to obtain the left trajectory circle of the outermost convex point of the outer surface of the car when turning left and the right trajectory circle of the outermost convex point of the outer surface of the car when turning right. The minimum value of the radii of the left trajectory circle and the right trajectory circle is taken as the turning radius of the car.

[0015] Furthermore, the scanning positioning point is a circular patch with a reflective front and an adhesive back, with a white circle in the middle of the front and a black ring around it.

[0016] Furthermore, the distance between the centers of adjacent scanning positioning points is 1-15 cm.

[0017] Furthermore, the transition plate is perpendicular to the ground, and the top of the transition plate contacts the bottom of the front bumper.

[0018] Furthermore, the Creaform 3D laser scanning equipment system collects the coordinates of the scanning positioning points and processes them to obtain a 3D point cloud image.

[0019] Further, processing the horizontal plane 3D point cloud image, the non-corner 3D point cloud image, the left-turn 3D point cloud image, and the right-turn 3D point cloud image includes:

[0020] Fit the horizontal plane 3D point cloud image to generate a reference plane;

[0021] The 3D point cloud image without corners and the two left-turning 3D point cloud images are projected onto the fitted reference plane to obtain three maximum outer contours of the left turn, and the boundary curves of the three maximum outer contours are generated, and the tangent circles are generated according to the three boundary curves as the left trajectory circle;

[0022] The 3D point cloud image without corners and the two right-turn 3D point cloud images are projected onto the fitted reference plane respectively to obtain the three maximum outer contours of the right turn, and the boundary curves of the three maximum outer contours are generated. According to the three boundary curves, a tangent circle is generated as the right trajectory circle.

[0023] Furthermore, after the reference plane is generated, the size deviation between the 3D point cloud image and the reference plane is measured. If the deviation is within the set range, the reference plane is qualified; if the deviation exceeds the set range, several points in the 3D point cloud image are reselected for fitting until the deviation is within the set range.

[0024] Furthermore, each point on the reference plane forms a projection point on the horizontal plane 3D point cloud image along the normal direction of the reference plane, and the distance between each point and the corresponding projection point is calculated respectively, and the maximum value of the calculated distances is taken as the deviation.

[0025] Further, the following steps are included:

[0026] 1) Park the car on a horizontal plane, keep the steering wheel at a fixed angle, arrange the first scanning positioning point in the horizontal plane area in front of the front of the car, collect the first scanning positioning point and process it to obtain a horizontal plane 3D point cloud image;

[0027] 2) Arrange a transition plate under the front bumper of the car, arrange a second scanning positioning point and a third scanning positioning point on the front bumper and the transition plate respectively, collect the second scanning positioning point and the third scanning positioning point and process them to obtain a corner-free 3D point cloud image of the front bumper;

[0028] 3) Remove the transition plate, keep the steering wheel at the left extreme turning angle, move the car forward a short distance, readjust the position of the transition plate, collect the second scanning positioning point and the third scanning positioning point, and process them to obtain the first left turn 3D point cloud image of the front bumper;

[0029] 4) Remove the transition plate, keep the steering wheel at the left extreme turning angle, and continue to move the car forward for a short distance. Re-adjust the position of the transition plate, collect the second scanning positioning point and the third scanning positioning point, and process them to obtain the second left turn 3D point cloud image of the front bumper;

[0030] 5) Keep the steering wheel at the right extreme turning angle, repeat steps 3) and 4) to obtain the first right turn 3D point cloud image and the second right turn 3D point cloud image of the bumper respectively;

[0031] 6) Fit the horizontal plane 3D point cloud image to obtain the reference plane,

[0032] 7) Projecting the 3D point cloud image without corners, the first left-turn 3D point cloud image and the second left-turn 3D point cloud image into the fitted reference plane respectively to obtain the three maximum outer contours of the left turn, and generating boundary curves of the three maximum outer contours, and generating tangent circles according to the three boundary curves as the left trajectory circle;

[0033] 8) Projecting the 3D point cloud image without corners, the first right-turn 3D point cloud image and the second right-turn 3D point cloud image into the fitted reference plane respectively to obtain three maximum outer contours of the right turn, and generating boundary curves of the three maximum outer contours, and generating tangent circles according to the three boundary curves as the right trajectory circle;

[0034] 9) Take the minimum value of the radius of the left track circle and the right track circle as the turning radius of the car.

[0035] Furthermore, after the car turns left and right and travels two distances respectively, the distance between the center of the first scanning positioning point on the horizontal plane and the center of the adjacent third scanning positioning point on the transition plate is 1-15 cm.

[0036] Through scanning and data processing, the present invention can quickly, effectively and accurately obtain the outermost contour line of the turn without the help of other tools or equipment, and can present 3D visualization results, which solves the problem that the outermost convex point of the turn cannot be determined. Through circumscribed circle fitting, the minimum turning radius can be quickly and accurately obtained with high accuracy, which can reach 0.1mm. At the same time, during the measurement process, the car only needs to drive forward a short distance at the extreme turning angle without making a complete 360° turn, and the measurement occupies a small space. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of arranging the first scanning positioning points in the horizontal plane area in front of the vehicle according to the present invention.

[0038] Figure 2 It is a schematic diagram of arranging the second scanning positioning point and the third scanning positioning point on the front bumper and the transition plate of the automobile respectively according to the present invention.

[0039] Figure 3 This is a schematic diagram of the steering wheel of the present invention maintaining the left limit turning angle and the car moving forward a short distance.

[0040] Figure 4 The schematic diagram of the present invention is that the steering wheel maintains the left limit turning angle and the automobile continues to move forward for a short distance.

[0041] Figure 5 Schematic diagram of three 3D point cloud images of the bumper obtained when the steering wheel is turned right to the limit according to the present invention.

[0042] Figure 6 It is a schematic diagram of boundary curves of the three outermost outer contours generated when the steering wheel is in the extreme right turn state of the present invention.

[0043] Figure 7 It is a schematic diagram of the right trajectory circle of the outermost convex point on the outer surface of the automobile when the steering wheel turns right to the limit according to the present invention.

[0044] In the figure, 1-car; 2-first scanning positioning point; 3-second scanning positioning point; 4-third scanning positioning point; 5-front bumper; 6-transition plate; 7-boundary line; 8-tangent circle; 9-ground. DETAILED DESCRIPTION

[0045] The specific embodiments of the present invention are further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0046] In order to measure the minimum turning radius of a car, it is necessary to determine the outermost convex point of the turn to determine the trajectory circle. However, the outer surface of the car is curved and has an irregular shape, so general tools and methods cannot accurately determine it.

[0047] The present invention utilizes Creaform 3D laser scanning equipment system (MAXShot Next photogrammetry positioning system + HandyScan 700 3D laser scanner) and the principle of laser scanning to obtain 3 groups of 3D point clouds of the front bumper during the extreme corner turning of the car, project the point clouds to obtain the maximum contour surface, generate 3 groups of boundary lines of the contour surfaces, and fit the circumscribed circles of the 3 groups of boundary lines. The tangent point is the outermost convex point of the turn, and the radius of the circumscribed circle is the minimum turning radius of the car. This is a digital solution.

[0048] According to the above principle, the present invention provides a method for measuring the minimum turning radius of an automobile, wherein scanning positioning points are arranged on the front of the automobile, the front bumper and the transition plate, and the coordinates of each scanning positioning point are collected and processed to obtain a 3D point cloud image of the horizontal plane and a 3D point cloud image of the front bumper without turning corners. The point cloud is a point set generated by a large amount of point coordinate information collected by a three-dimensional laser scanning instrument by irradiating the surface of an object, and a 3D point cloud image is formed by acting on the interface;

[0049] Control the steering wheel to turn left to the limit angle, move forward two distances in sequence, collect the scanning positioning point coordinates of the front bumper at two positions respectively, and process them to obtain two left-turn 3D point cloud images of the front bumper;

[0050] Control the steering wheel to turn right to the limit angle, move forward two distances in sequence, collect the scanning positioning point coordinates of the front bumper at two positions respectively, and process them to obtain two right-turn 3D point cloud images of the front bumper;

[0051] The horizontal plane 3D point cloud image, the 3D point cloud image without turning corners, the left-turn 3D point cloud image and the right-turn 3D point cloud image are processed to obtain the left trajectory circle of the outermost convex point of the outer surface of the car when turning left and the right trajectory circle of the outermost convex point of the outer surface of the car when turning right. The average of the radii of the left trajectory circle and the right trajectory circle is taken as the turning radius of the car.

[0052] In the above scheme, the scanning positioning point is a circular patch with reflective properties on the front and adhesive on the back, which is used for coordinate positioning. The middle of the front is a white circle and the surrounding is a black ring. Of course, as long as the front has certain reflective properties, it is not limited to white and black.

[0053] In the above scheme, in order to facilitate identification of all scanning positioning points and then positioning, the distance between the centers of adjacent scanning positioning points needs to be within a certain range. In the present invention, the range is selected as 1-15 cm, preferably 5 cm or 10 cm.

[0054] The following is a detailed description of the method for measuring the minimum turning radius of an automobile according to the present invention in conjunction with the accompanying drawings:

[0055] Step 1: Park the car on a horizontal surface, keep the steering wheel at a fixed angle, and arrange the first scanning positioning point in the horizontal area in front of the car, such as Figure 1 As shown, the arranged horizontal plane area needs to ensure that after the car has traveled two distances for extreme left and right turns respectively, the distance between its first scanning positioning point and the center of the adjacent third scanning positioning point on the transition plate below is still within the set range, so as to ensure that the position of the scanning positioning point can still be identified after the car has traveled a certain distance.

[0056] Step 2: Open the VXShot module of the VXelements software, use the MAXShot Next photogrammetry system to complete the photogrammetry positioning of the scanning positioning points, and output a positioning point file (txt format) containing the positions of all the first scanning positioning points (i.e., the coordinates in the coordinate system calibrated by the measurement system).

[0057] Step 3: Open the VXScan module of the VXelements software, import the positioning point file in step 2, perform a 3D point cloud scan of the horizontal plane, and output the scan file (i.e., the horizontal plane 3D point cloud image) (stl format).

[0058] Step 4: Arrange the second scanning positioning point on the front bumper of the car (or the skin); arrange the third scanning positioning point on the transition plate and place it between the ground and the front bumper, such as Figure 2As shown, the transition plate is perpendicular to the ground, and the top of the transition plate contacts the bottom of the front bumper. The distance between the front bumper and the ground is generally large. If scanning positioning points are only arranged on the front bumper and the ground, the distance between the adjacent scanning positioning points is large and may not be recognized. Therefore, a transition plate is arranged between the two, and a third scanning positioning point is arranged on the transition plate to form a transition area to connect the scanning positioning points on the front bumper and the ground, which is easy to identify.

[0059] Step 5: In the VXScan module of the VXelements software, import the positioning point file of step 2, use the transition plate to complete the transition and identification of the second scanning positioning point on the front bumper, perform a 3D point cloud scan of the front bumper, and output the scan file (i.e., 3D point cloud image without corners) (stl format).

[0060] Step 6: Remove the transition plate, keep the steering wheel at the left extreme angle, and move the car forward a short distance. Figure 3 As shown, the distance traveled depends on the area of ​​the first scanning positioning point arranged on the horizontal plane. As long as the distances of the two travels do not exceed the horizontal plane area where the first scanning positioning point is arranged, the distances of the two travels can be the same or different. Re-adjust the position of the transition plate, import the positioning point file of step 2 in the VXelements software VXScan module, use the transition plate to complete the transition and identification of the second scanning positioning point on the front bumper in this state, perform a 3D point cloud scan of the front bumper, and output the scan file (i.e., the first left turn 3D point cloud image) (stl format).

[0061] Step 7: Remove the transition plate, keep the steering wheel at the left limit angle, and continue to move the car forward for a short distance. Figure 4 As shown, readjust the position of the transition plate, import the positioning point file of step 2 in the VXScan module of the VXelements software, use the transition plate to complete the transition and identification of the second scanning positioning point on the front bumper in this state, perform a 3D point cloud scan of the front bumper skin, and output the scan file (i.e., the second left-turn 3D point cloud image) (stl format).

[0062] Step 8: Keep the steering wheel at the right limit angle, repeat steps 6 and 7, and obtain the first right turn 3D point cloud image and the second right turn 3D point cloud image of the bumper, as shown in Figure 5 shown.

[0063] Step 9: Through steps 1 to 8, 6 3D point cloud scanning files are obtained, which are horizontal plane point clouds and 3D point clouds of the front bumper skin at 5 different positions (car turning left, car turning right), all of which are imported into Catia software.

[0064] Step 10: In Catia software, fit the horizontal point cloud to a plane, select the "Create Plane-Average Through Points" command, click and select no less than 10 points on the point cloud to fit the digital geometric reference plane; after generating the reference plane, measure the deviation △ between the horizontal point cloud and the reference plane. If △ is within the range of ±0.1mm, the reference plane is considered qualified. If △ exceeds the range of ±0.1mm, reselect points for fitting until it is qualified. Among them, each point on the reference plane forms a projection point on the horizontal plane 3D point cloud image along the normal direction of the reference plane, and the distance between each point and the corresponding projection point is calculated respectively. The maximum value of the calculated distance is taken as the deviation. The smaller the absolute value of the deviation, the closer the reference plane generated by fitting is to the actual ground, and the higher the accuracy of the minimum turning radius finally measured.

[0065] Step 11: Take the 3D point cloud image of the front bumper at three different positions of the car's left turn state (including no turning angle and two left extreme turning angles), select the "Point Cloud Projection" command, project the point cloud into the fitted reference plane, and obtain the three maximum outer contours; select the "Boundary Line" command to generate the boundary curves of the outermost contours of the three positions.

[0066] Step 12: Select the "Create Circle - Tangent Circle" command, select 3 boundary curves, and generate a tangent circle. The tangent circle is the left trajectory circle of the outermost convex point on the outer surface of the car when turning left. Measure the radius of the left trajectory circle, which is the minimum turning radius R1 when the car turns left.

[0067] Step 13: Repeat steps 11 and 12 for the 3D point cloud of the front bumper at three different positions of the car's right turn state to obtain the minimum turning radius R2 when the car turns right, as shown in Figure 6 , Figure 7 shown.

[0068] Step 14: Compare the sizes of R1 and R2, and take the minimum value of the two as the minimum turning radius of the car.

[0069] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in the field.

Claims

1. A method for measuring the minimum turning radius of an automobile, characterized in that: Arrange scanning positioning points on the front of the car, the front bumper and the transition plate respectively, collect the coordinates of each scanning positioning point and process them to obtain a horizontal plane 3D point cloud image and a non-corner 3D point cloud image of the front bumper; Control the steering wheel to turn left to the limit angle, move forward two distances in sequence, collect the scanning positioning point coordinates of the front bumper at two positions respectively, and process them to obtain two left-turn 3D point cloud images of the front bumper; Control the steering wheel to turn right to the limit angle, move forward two distances in sequence, collect the scanning positioning point coordinates of the front bumper at two positions respectively, and process them to obtain two right-turn 3D point cloud images of the front bumper; The horizontal plane 3D point cloud image, the 3D point cloud image without turning corners, the left-turn 3D point cloud image and the right-turn 3D point cloud image are processed to obtain the left trajectory circle of the outermost convex point of the outer surface of the car when turning left and the right trajectory circle of the outermost convex point of the outer surface of the car when turning right. The minimum value of the radii of the left trajectory circle and the right trajectory circle is taken as the turning radius of the car.

2. The method for measuring the minimum turning radius of an automobile according to claim 1, characterized in that: The scanning positioning point is a circular patch with a reflective front and an adhesive back, with a white circle in the middle of the front and a black ring around it.

3. The method for measuring the minimum turning radius of an automobile according to claim 1, characterized in that: The distance between the centers of adjacent scanning positioning points is 1-15cm.

4. The method for measuring the minimum turning radius of an automobile according to claim 1, characterized in that: The transition plate is perpendicular to the ground, and the top of the transition plate contacts the bottom of the front bumper.

5. The method for measuring the minimum turning radius of an automobile according to claim 1, characterized in that: The Creaform 3D laser scanning system collects the coordinates of the scanning positioning points and processes them to obtain a 3D point cloud image.

6. The method for measuring the minimum turning radius of an automobile according to claim 1, characterized in that: Processing of the horizontal plane 3D point cloud image, the non-corner 3D point cloud image, the left-turn 3D point cloud image and the right-turn 3D point cloud image includes: Fit the horizontal plane 3D point cloud image to generate a reference plane; The 3D point cloud image without corners and the two left-turning 3D point cloud images are projected onto the fitted reference plane to obtain three maximum outer contours of the left turn, and the boundary curves of the three maximum outer contours are generated, and the tangent circles are generated according to the three boundary curves as the left trajectory circle; The 3D point cloud image without corners and the two right-turn 3D point cloud images are projected onto the fitted reference plane respectively to obtain the three maximum outer contours of the right turn, and the boundary curves of the three maximum outer contours are generated. According to the three boundary curves, a tangent circle is generated as the right trajectory circle.

7. The method for measuring the minimum turning radius of an automobile according to claim 6, characterized in that: After the reference plane is generated, the deviation between the 3D point cloud image and the reference plane is measured. If the deviation is within the set range, the plane is qualified; if the deviation exceeds the set range, several points in the 3D point cloud image are reselected for fitting until the deviation is within the set range.

8. The method for measuring the minimum turning radius of an automobile according to claim 7, characterized in that: Each point on the reference plane forms a projection point on the horizontal plane 3D point cloud image along the normal direction of the reference plane, and the distance between each point and the corresponding projection point is calculated respectively, and the maximum value of the calculated distances is taken as the deviation.

9. The method for measuring the minimum turning radius of an automobile according to claim 1, characterized in that: The following steps are included 1) Park the car on a horizontal plane, keep the steering wheel at a fixed angle, arrange the first scanning positioning point in the horizontal plane area in front of the front of the car, collect the first scanning positioning point and process it to obtain a horizontal plane 3D point cloud image; 2) Arrange a transition plate under the front bumper of the car, arrange a second scanning positioning point and a third scanning positioning point on the front bumper and the transition plate respectively, collect the second scanning positioning point and the third scanning positioning point and process them to obtain a corner-free 3D point cloud image of the front bumper; 3) Remove the transition plate, keep the steering wheel at the left extreme turning angle, move the car forward a short distance, readjust the position of the transition plate, collect the second scanning positioning point and the third scanning positioning point, and process them to obtain the first left turn 3D point cloud image of the front bumper; 4) Remove the transition plate, keep the steering wheel at the left extreme turning angle, and continue to move the car forward for a short distance. Re-adjust the position of the transition plate, collect the second scanning positioning point and the third scanning positioning point, and process them to obtain the second left turn 3D point cloud image of the front bumper; 5) Keep the steering wheel at the right extreme turning angle, repeat steps 3) and 4) to obtain the first right turn 3D point cloud image and the second right turn 3D point cloud image of the bumper respectively; 6) Fit the horizontal plane 3D point cloud image to obtain the reference plane, 7) Projecting the 3D point cloud image without corners, the first left-turn 3D point cloud image and the second left-turn 3D point cloud image into the fitted reference plane respectively to obtain the three maximum outer contours of the left turn, and generating boundary curves of the three maximum outer contours, and generating tangent circles according to the three boundary curves as the left trajectory circle; 8) Projecting the 3D point cloud image without corners, the first right-turn 3D point cloud image and the second right-turn 3D point cloud image into the fitted reference plane respectively to obtain three maximum outer contours of the right turn, and generating boundary curves of the three maximum outer contours, and generating tangent circles according to the three boundary curves as the right trajectory circle; 9) Take the minimum value of the radius of the left track circle and the right track circle as the turning radius of the car.

10. The method for measuring the minimum turning radius of an automobile according to claim 9, characterized in that: After the car turns left and right and travels two distances respectively, the distance between the center of the first scanning positioning point on the horizontal plane and the center of the adjacent third scanning positioning point on the transition plate is 1-15 cm.

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