A method for positioning the center point of a tire

Abstract

The present invention relates to the field of computer vision three-dimensional measurement and intelligent transportation technology, and discloses a tire center point positioning method, step 1: using the Ransac space circle fitting method to fit the tire point cloud set tire to obtain an initial circle; step 2: in the plane where the initial circle is located, find all point clouds P in a ring with O0 (x0, y0, z0) as the circle center, R0 as the inner circle radius, and R0+D as the outer circle radius. i ; Step 3: Calculate all point clouds P in the ring i The difference δ between the average coordinate value of and the coordinate value of the initial center O0 (x0, y0, z0) x , δ y , δ z ; Step 4: Update the initial circle center coordinate value and the initial circle radius; Step 5: Enter the step 2 loop until the number N of point clouds found in the ring is 0; By using the method of the present invention to locate the tire center point, it can be unaffected by the uneven distribution of point clouds on the tire surface and the incomplete point clouds at the edge of the tire, and the tire center point position can be accurately fitted.

Description

Technical Field

[0001] The present invention relates to the field of computer vision three-dimensional measurement and intelligent transportation technology, and in particular to a method for locating the tire center point by fitting the minimum circumscribed circle of a tire point cloud and then based on the center position of the minimum circumscribed circle. Background Art

[0002] With the continuous development of computer vision 3D measurement, it is now being used in the intelligent transportation sector to achieve non-contact measurement of vehicle dimensions and wheelbase. To measure wheelbase, the tire center must be located. The wheelbase can be calculated based on the positions of the front and rear tire centers. Therefore, tire center location is a critical step in vehicle wheelbase measurement.

[0003] Based on the circular shape of the tire, the positioning of the tire center point can be converted into the fitting of a space circle. Currently, many scholars have proposed different space circle fitting methods, among which the technical solution that is closer to the present invention is: Reference (Feng Dinghao, Zhang Xi, et al. Spatial circle fitting algorithm based on RANSAC and its application in manipulator motion detection [J]. Optical Technology, 2016, 42 (2): 156-160.) proposed to directly use the Ransac space circle fitting method to fit the manipulator motion trajectory. Once the density of the point cloud is uneven during the fitting process, the Ransac method will make the fitted space circle move toward the point cloud density in order to make more points belong to the inner point. The larger directional deviation, and if the point cloud is incomplete at the edge of the tire during tire circle fitting, the fitted circle will also be offset in the opposite direction of the incomplete position; the literature (Li Xu. Application of spatial circle fitting method in subway tunnel portal coordinate calculation [J]. Surveying and Spatial Geographic Information, 2015, 38 (3): 177-181.) proposed to first use the least squares method to fit the plane where the subway tunnel portal is located, and then use the plane equation as a constraint condition to perform the least squares method spatial sphere fitting. The circle formed by the intersection of the fitted sphere and the plane is the fitted spatial circle. In order to minimize the error of the least squares method, the circle fitted by this method will also shift towards the direction with higher point cloud density or more point clouds; the literature (Tian Xiao, Li Quanhai. A new method for spatial circle fitting detection based on projection points [J]. Engineering Survey, 2014 (5): 72-74.) also proposed to first perform plane fitting on the spatial point cloud, then project all points onto the plane, and use the geometric relationship between the projection points and the center of the circle to list the error equation, and solve the equation with the center of the circle on the plane as the constraint condition to obtain the center and radius of the fitted circle. This method has high requirements for the collected point cloud data, and uneven point cloud density will also cause deviations in the fitted circle. The tire point cloud data obtained by laser radar scanning often has uneven density distribution.

[0004] In summary, the current spatial circle fitting method has the following shortcomings when applied to tire center point positioning: (1) It has high requirements for the distribution of tire point clouds. The uneven distribution of point clouds on the tire surface will cause deviations in the fitted spatial circle; (2) It cannot be correctly fitted when there are incomplete point clouds at the edge of the tire. Summary of the Invention

[0005] In response to the above-mentioned problems existing in the existing spatial circle fitting method when applied to tire center point positioning, the present invention proposes a method for fitting the minimum circumscribed circle of the tire point cloud and then positioning the tire center point based on the center position of the minimum circumscribed circle.

[0006] The technical solutions of the present invention are as follows:

[0007] A tire center point positioning method includes the following steps:

[0008] Step 1: Use the Ransac space circle fitting method to fit the tire point cloud set tire to obtain an initial circle. The center of the circle is recorded as O0 (x0, y0, z0) and the radius is recorded as R0, where (x0, y0, z0) are the coordinate values of the center of the circle;

[0009] Step 2: In the plane of the initial circle, find all point clouds P in the circle with O0(x0,y0,z0) as the center, R0 as the inner radius, and R0+D as the outer radius. i , i=1,2,…,N, where D represents the pre-set expansion distance, P i represents the i-th point cloud in the ring, and N represents the number of point clouds in the ring;

[0010] Step 3: Calculate all point clouds P in the ring according to formula (1) i The difference δ between the average coordinate value of and the coordinate value of the initial center O0 (x0, y0, z0) x , δ y , δ z ;

[0011]

[0012] Among them, (x i ,y i , z i ) represents the i-th point cloud P in the ring i The coordinate value of

[0013] Step 4: Update the initial circle center coordinates according to formula (2), and update the initial circle radius according to formula (3);

[0014]

[0015]

[0016] Where scale represents the update step value calculated according to formula (4);

[0017]

[0018] Step 5: Enter the loop of step 2 until the number of point clouds N found in the ring is 0. At this time, O0 (x0, y0, z0) and R0 are the center point and radius of the tire respectively.

[0019] The beneficial effects of the present invention are as follows: by using the method of the present invention to locate the center point of the tire, it can accurately fit the position of the tire center point without being affected by the uneven distribution of the point cloud on the tire surface and the incomplete point cloud at the edge of the tire. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A tire point cloud set tire map selected in an embodiment of the present invention;

[0021] Figure 2 This is a diagram showing the center point positioning results of the tire in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The following describes in detail the specific implementation of the tire center point positioning method of the present invention in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] A tire center point positioning method of the present invention comprises the following steps:

[0024] Step 1: Use the Ransac space circle fitting method to fit the tire point cloud set tire to obtain an initial circle. The center of the circle is recorded as O0 (x0, y0, z0), and the radius is recorded as R0, where (x0, y0, z0) is the coordinate value of the center of the circle. In this embodiment, the tire point cloud set tire is selected as follows: Figure 1 As shown, the Ransac space circle fitting distance threshold is set to 40 mm and the maximum number of iterations is 10,000;

[0025] Step 2: In the plane of the initial circle, find all point clouds P in the circle with O0(x0,y0,z0) as the center, R0 as the inner radius, and R0+D as the outer radius. i , i=1,2,…,N, where D represents the pre-set expansion distance, P i represents the i-th point cloud in the ring, N represents the number of point clouds in the ring, and in this embodiment, D is set to 10 mm;

[0026] Step 3: Calculate all point clouds P in the ring according to formula (1) i The difference δ between the average coordinate value of and the coordinate value of the initial center O0 (x0, y0, z0) x , δ y , δ z ;

[0027]

[0028] Among them, (x i ,y i , z i ) represents the i-th point cloud P in the ring i The coordinate value of

[0029] Step 4: Update the initial circle center coordinates according to formula (2), and update the initial circle radius according to formula (3);

[0030]

[0031]

[0032] Where scale represents the update step value calculated according to formula (4);

[0033]

[0034] Step 5: Enter step 2 and loop until the number of point clouds N found in the ring is 0. At this time, O0 (x0, y0, z0) and R0 are the center point and radius of the tire respectively. In this embodiment, the center point of the tire is located as follows: Figure 2 As shown, it can be seen that the center point of the tire is accurately located.

Claims

1. A tire center point positioning method, characterized in that: The steps include: Step 1: Use the Ransac space circle fitting method to fit the tire point cloud set tire to obtain an initial circle. The center of the circle is recorded as O0 (x0, y0, z0) and the radius is recorded as R0, where (x0, y0, z0) are the coordinate values of the center of the circle; Step 2: In the plane of the initial circle, find all point clouds P in the ring with O0(x0,y0,z0) as the center, R0 as the inner radius, and R0+D as the outer radius. i , i=1,2,…,N, where D represents the pre-set expansion distance, P i represents the i-th point cloud in the ring, and N represents the number of point clouds in the ring; Step 3: Calculate all point clouds P in the ring according to formula (1) i The difference δ between the average coordinate value of and the coordinate value of the initial center O0 (x0, y0, z0) x , δ y , δ z ; Among them, (x i ,y i , z i ) represents the i-th point cloud P in the ring i The coordinate value of Step 4: Update the initial circle center coordinates according to formula (2), and update the initial circle radius according to formula (3); Where scale represents the update step value calculated according to formula (4); Step 5: Enter the loop of step 2 until the number of point clouds N found in the ring is 0. At this time, O0 (x0, y0, z0) and R0 are the center point and radius of the tire respectively.

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