Method and device for calculating chord height of central spherical surface of front windshield of vehicle

Abstract

The invention discloses a vehicle front windshield center spherical chord height calculation method and device, and the method comprises the steps: obtaining the point cloud information of a triangular point cloud grid file, calculating the height average value of the Y-axis coordinate components of all grid vertexes, building a height reference plane according to the height average value, and enabling the Y-axis coordinates of the height reference plane to be equal to the height average value; according to the height reference plane and the point cloud information, determining intersection points of a triangular point cloud grid of the front windshield model and the height reference plane; determining a spherical chord end point according to the value of the X-axis coordinate of the intersection point, and determining the chord length according to the coordinate of the spherical chord end point; taking the intersection point as a type value point of the segmented spline curve, expressing the segmented spline curve as a segmented cubic B-spline function by using a second derivative at the type value point, and according to the condition that a first derivative of the cubic B-spline function at the type value point is continuous and parabolas at the first segment and the last segment of the segmented spline curve are taken as boundary conditions, calculating the boundary of the segmented spline curve. Determining a second derivative value at the type value point, and determining a cubic B-spline function according to the second derivative value at the type value point; sampling points on the segmented spline curve according to the preset step length of the X-axis coordinate component, and respectively calculating the distance from each sampling point to the spherical chord, so that the height of the central spherical chord is equal to the maximum value of the distance.

Description

Technical Field

[0001] The present invention relates to the technical field of a method for calculating central spherical surface parameters of a front windshield in a vehicle development stage, and in particular to a method and device for calculating the central spherical surface chord height of a front windshield of a vehicle. Background Art

[0002] During the automobile development process, the geometric characteristics of the automobile windshield need to be analyzed to ensure process formability, among which chord height is an important geometric parameter. However, in the early concept development stage, the point cloud data obtained by scanning the clay model is a discrete surface, and it is impossible to use CAD engineering software such as Catia and UG to measure the chord height.

[0003] When measuring the chord height of front and rear windshields, most OEMs first generate shape data and surface data, and then measure them using CAD engineering software such as Catia and UG. Generating shape data and surface data first and then measuring chord height requires additional manpower and is time-consuming, which affects development efficiency. Summary of the invention

[0004] In order to solve at least one aspect of the above problems, the present invention provides a method for calculating the central spherical chord height of a vehicle windshield, comprising: obtaining a windshield model, generating a triangular point cloud mesh file based on the windshield model; reading point cloud information in the triangular point cloud mesh file, calculating the height average of the Y-axis coordinate components of all mesh vertices according to the point cloud information, creating a height reference plane according to the height average, the height reference plane being a plane perpendicular to the Y-axis, and the Y-axis coordinate of the height reference plane being equal to the height average; determining the intersection of the triangular point cloud mesh of the windshield model and the height reference plane according to the height reference plane and the point cloud information; and The endpoints of the spherical chord are determined according to the values ​​of the X-axis coordinates of the intersection points, and the chord length is determined according to the coordinates of the endpoints of the spherical chord; the intersection points are used as the form value points of the piecewise spline curve, and the piecewise spline curve is expressed as a piecewise cubic B-spline function using the second-order derivatives at the form value points. According to the continuity of the first-order derivatives of the cubic B-spline function at the form value points, and the first and last segments of the piecewise spline curve are parabolas as boundary conditions, the second-order derivative values ​​at the form value points are determined, and the cubic B-spline function is determined according to the second-order derivative values ​​at the form value points; sampling points are taken on the piecewise spline curve according to the preset step size of the X-axis coordinate component, and the distances from each sampling point to the spherical chord are calculated respectively, and the height of the central spherical chord is equal to the maximum value of the distance.

[0005] Preferably, the step of determining the intersection of the triangular point cloud mesh of the front windshield model with the height reference plane according to the height reference plane and the point cloud information further includes: traversing the triangular point cloud mesh, determining the number of intersections of each triangular point cloud mesh with the high-speed reference plane, and respectively calculating the product of the difference between the Y-axis component of the vertex of each triangular point cloud mesh and the height average value; when d1d2<0 and d1d3<0, finding the intersection of P1P2, P1P3 with the high-speed reference plane; when d1d2<0 and d2d3<0, finding P1P 2. The intersection of P2P3 and the high-speed reference plane; when d1d3<0 and d2d3<0, find the intersection of P1P3, P2P3 and the high-speed reference plane; when one of d1, d2, and d3 is zero, determine the product of the other two. If the product is greater than zero, the intersection is not saved. If the product is less than zero, the intersection is calculated and saved. If the product is equal to zero, the two vertices are saved, where P1, P2, and P3 are vertices of the triangular point cloud mesh, respectively, and d1, d2, and d3 are the differences between P1, P2, and P3 and the average height.

[0006] Preferably, the step of determining the intersection of the triangular point cloud mesh of the front windshield model and the height reference plane based on the height reference plane and the point cloud information also includes: obtaining the X-axis coordinate component of the intersection, and deleting one intersection when the difference between the X-axis coordinate components of the two intersections is less than a preset threshold.

[0007] Preferably, the preset step size is 0.01.

[0008] On the other hand, a device for calculating the center spherical chord height of a vehicle's front windshield is provided, characterized in that it includes a memory and a processor, the memory includes a computer program, and the computer program, when executed by the processor, executes the method for calculating the center spherical chord height of the vehicle's front windshield as described in any of the above.

[0009] The method and device for calculating the chord height of the central spherical surface of the front windshield of a vehicle according to an embodiment of the present invention have the following beneficial effects: by averaging the coordinate components of the y-axis of all vertices to obtain a value of m, a height reference plane is created, and the plane created and the triangular mesh of the curved surface will have intersections, and these intersections are obtained by a program, and redundant points are removed. These intersections can be regarded as the form value points of the spline curve, and a matrix equation about the second-order derivative Mi at the form value points is established, and the second-order derivative Mi of these form value points is obtained by a program. The curve is represented as a segmented cubic B-spline curve using the second-order derivative Mi at the form value points, and the function expression of the curve of each segment is obtained. Points on the curve are taken at a step size of 0.01, and the distance from the point to the straight line is calculated. The maximum value of the distance is the chord height. It avoids the need to first create modeling data and surface data, so that the development efficiency is improved, and the process formability analysis of the front windshield of the automobile can be performed quickly and accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to better understand the above and other purposes, features, advantages and functions of the present invention, reference may be made to the embodiments shown in the accompanying drawings. The same reference numerals in the accompanying drawings refer to the same components. It should be understood by those skilled in the art that the accompanying drawings are intended to schematically illustrate the preferred embodiments of the present invention and have no limiting effect on the scope of the present invention, and the components in the drawings are not drawn to scale.

[0011] Figure 1 A flow chart showing a method for calculating the central spherical chord height of a front windshield of a vehicle according to an embodiment of the present invention is shown;

[0012] Figure 2 A schematic diagram showing the intersection of a triangular point cloud grid and a height reference plane according to a method for calculating the central spherical chord height of a front windshield of a vehicle according to an embodiment of the present invention;

[0013] Figure 3 A schematic diagram showing another intersection point of a triangular point cloud grid and a height reference plane according to a method for calculating the central spherical chord height of a front windshield of a vehicle according to an embodiment of the present invention;

[0014] Figure 4 A schematic diagram showing the central spherical chord height of a method for calculating the central spherical chord height of a front windshield of a vehicle according to an embodiment of the present invention

[0015] Figure 5 A schematic diagram of the central spherical chord height where the yz plane intersects the central spherical surface of the front windshield in a vehicle body coordinate system according to a method for calculating the central spherical chord height of the front windshield of a vehicle according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0016] The following is a description of exemplary embodiments of the present disclosure in conjunction with the accompanying drawings, including various details of the embodiments of the present disclosure to facilitate understanding, which should be considered as merely exemplary. Therefore, it should be recognized by those of ordinary skill in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present disclosure. Similarly, for the sake of clarity and conciseness, descriptions of well-known functions and structures are omitted in the following description.

[0017] As used herein, the term "including" and its variations mean open inclusion, i.e., "including but not limited to". Unless otherwise stated, the term "or" means "and / or". The term "based on" means "based at least in part on". The terms "an example embodiment" and "an embodiment" mean "at least one example embodiment". The term "another embodiment" means "at least one additional embodiment". The terms "first", "second", etc. may refer to different or the same objects. Other explicit and implicit definitions may also be included below.

[0018] In order to at least partially solve one or more of the above problems and other potential problems, the embodiment of the present disclosure proposes a method for calculating the central spherical chord height of the front windshield of a vehicle, such as Figure 4 As shown, the definition of the central sphere chord height is: the distance from a point on a curve of the Y0 section of the front windshield to the straight line connecting the two endpoints of the curve is the chord height, and the distance from the straight line connecting points A and B is the chord length. Figure 4 In the figure, L is the chord length and H is the maximum chord height, which is the distance from the point s to the straight line AB when the tangent line of the point on the curve is parallel to the straight line.

[0019] The method for calculating the spherical chord height of the center of the front windshield of a vehicle comprises: step 1, obtaining a front windshield glass model, and generating a triangular point cloud mesh file based on the front windshield glass model.

[0020] Specifically, CATIA exports a triangular point cloud mesh file of the surface model of the car's front windshield, and the mesh density is 0.2 mm.

[0021] Step 2: Read the point cloud information in the triangular point cloud mesh file, and calculate the average height of the Y-axis coordinate components of all mesh vertices based on the point cloud information.

[0022] Specifically, the point cloud information in the grid file is read in Python, and the value m is obtained by averaging the y-axis coordinate components of the vertices of the triangular point cloud grid.

[0023] Step 3: Create a height reference plane based on the height average value. The height reference plane is a plane perpendicular to the Y axis, and the Y axis coordinate of the height reference plane is equal to the height average value.

[0024] Specifically, by averaging the coordinate components of the y-axis of all vertices to obtain a value of m, a height reference plane of y=m is created.

[0025] Step 4: determine the intersection of the triangular point cloud mesh of the front windshield model and the height reference plane according to the height reference plane and the point cloud information.

[0026] Specifically, traverse the triangular point cloud mesh, determine the number of intersections between each triangular point cloud mesh and the high-speed reference plane, and calculate the product of the Y-axis component of the vertex of each triangular point cloud mesh and the height average difference. When d1d2<0 and d1d3<0, find the intersection of P1P2, P1P3 and the high-speed reference plane, such as Figure 2 As shown in pic1; when d1d2<0 and d2d3<0, find the intersection of P1P2, P2P3 and the high-speed reference plane, such as Figure 2 As shown in pic2; when d1d3<0 and d2d3<0, find the intersection of P1P3, P2P3 and the high-speed reference plane, such as Figure 2As shown in pic3; when one of d1, d2, and d3 is zero, the product of the other two is determined. If the product is greater than zero, the intersection point is not saved, such as Figure 3 As shown in pic4, if the product is less than zero, the intersection point is calculated and saved, such as Figure 3 As shown in pic5, if the product is zero, save the two vertices, such as Figure 3 As shown in pic6, P1, P2, and P3 are the vertices of the triangular point cloud mesh, and d1, d2, and d3 are the differences between P1, P2, and P3 and the average height.

[0027] In another embodiment, the value corresponding to the numerator of the distance formula from the vertex to the plane of each triangular point cloud mesh is calculated by removing the absolute value, specifically as follows: the distance formula from the point to the plane is:

[0028]

[0029] Among them, A, B, C, and D are the coefficients of the plane equation. For the height reference plane, the coefficient A is 0, B is 1, C is 0, and D is -m.

[0030] The coordinates of the intersection of the triangular point cloud mesh and the height reference plane have the following corresponding relationship with the vertices of the triangular point cloud mesh, taking the point P on the edge of P1P2 as 12 For example:

[0031] P 12 =P1+t(P2+P1), t=|d1| / (|d1|+|d2|).

[0032] Step 4, determine the endpoint of the spherical chord according to the value of the X-axis coordinate of the intersection point, and determine the chord length according to the coordinate of the endpoint of the spherical chord.

[0033] Specifically, after finding all the intersections of the height reference plane and the triangular point cloud grid, the intersections are saved as an intersection sequence in ascending order of the size of the X-coordinate component. In the process of finding the intersections, the same intersection may be found twice. In some embodiments, the X-axis coordinate component of the intersection is obtained, and when the difference between the X-axis coordinate components of the two intersections is less than a preset threshold, an intersection is deleted. For example, the intersections whose X-coordinate components differ by 0.000000001 are removed. Because all points are in the plane of y=m, these three-dimensional points can be simplified and viewed in a two-dimensional plane. Take out the first intersection and the last intersection in the intersection sequence. These two points determine a line segment, which is the chord length of the curve. The expression of this line segment is obtained based on an intersection and the last intersection, which is the central spherical chord.

[0034] Step 5, take the intersection point as the type value point of the piecewise spline curve, use the second-order derivative at the type value point to express the piecewise spline curve as a piecewise cubic B-spline function, according to the continuity of the first-order derivative of the cubic B-spline function at the type value point, and take the piecewise spline curve as a parabola in the first and last segments as the boundary condition, determine the second-order derivative value at the type value point, and determine the cubic B-spline function based on the second-order derivative value at the type value point.

[0035] Specifically, the intersection point is used as the shape point of the piecewise spline curve, and the second-order derivative M at the shape point is used as i The curve is represented as a segmented cubic B-spline function. For example, if there are 60 intersection points, the curve can be divided into 59 small segments, and each segment is expressed as follows:

[0036]

[0037] Utilize i (x) in P i The first-order derivative at the point is continuous, and the M at the point of the model value is solved. i ,

[0038] s i ′ (x) = b i +2c i (xx i )+3d(xx i ) 2 ,s i ′ -1 (x) = s i ′ (x),

[0039] in,

[0040] Then, λ i M i-1 +2M i +μ i M i+1 =D i ,

[0041] At this time, i=2,…,n-1; λ i +μ i =1.

[0042] There are n-2 equations in the above formula, and M cannot be solved uniquely. i . It is necessary to use boundary conditions to uniquely solve a set of M and then determine the cubic B-spline function of the point. Assume that the first and n-1 segments of the curve are parabolic segments, that is, the second-order derivative is a non-zero constant.

[0043] Let y1 ″ =y2 ″ ,y ′ n ′ -1 =y2 ″ n , 2M1-2M2=0, -2M n-1 +2M n = 0. Combine this boundary condition with D i The formulas of can form a complete linear equation system, which can be expressed as a matrix:

[0044]

[0045] Using Python programming, find the coefficient matrix on the left side of the matrix equation and the matrix on the right side of the equation to solve M i The value of M i The value of determines the function expression corresponding to the piecewise spline curve.

[0046] Step 6: Sample points on the piecewise spline curve according to the preset step size of the X-axis coordinate component, and calculate the distance from each sample point to the spherical chord. The height of the central spherical chord is equal to the maximum value of the distance.

[0047] Specifically, through s i The curve expression of each segment of the spline curve is established by using the expression of (x). Sample points are taken on each small segment of the curve with a step size of 0.01 on the X-axis coordinate component. The distance from the sample point to the central spherical chord is calculated. All the curve segments are traversed in turn. For example, the number of sample points taken in all small segments is 73488. The maximum value of the distances obtained is taken. The maximum distance is the maximum chord height H.

[0048] like Figure 5 As shown, curve BB is obtained by the intersection of the yz plane and the curved surface in the vehicle body coordinate system, and the chord height is 18.138mm and the chord length is 862.031mm. For curve BB, the relative chord height H is defined as r :

[0049]

[0050] Table 1

[0051]

[0052] The calculation results of the vehicle front windshield center spherical chord height shown in Table 1 are compared with the software measurement values. It can be seen that the error is less than 0.03%, which is very accurate.

[0053] On the other hand, a device for calculating the central spherical chord height of a vehicle's front windshield is provided, characterized in that it includes a memory and a processor, the memory includes a computer program, and the computer program, when executed by the processor, executes the method for calculating the central spherical chord height of a vehicle's front windshield as described above.

[0054] The embodiments of the present disclosure have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the present invention.

Claims

1. A method for calculating the central spherical chord height of a vehicle front windshield, characterized in that: include: Acquire a front windshield model, and generate a triangular point cloud mesh file based on the front windshield model; Reading point cloud information in the triangular point cloud mesh file, and calculating the average height of the Y-axis coordinate components of all mesh vertices according to the point cloud information; Creating a height reference plane according to the height average value, wherein the height reference plane is a plane perpendicular to the Y axis, and the Y axis coordinate of the height reference plane is equal to the height average value; Determine an intersection point of a triangular point cloud grid of the front windshield model and the height reference plane according to the height reference plane and the point cloud information; Determine the endpoint of the spherical chord according to the value of the X-axis coordinate of the intersection point, and determine the chord length according to the coordinate of the endpoint of the spherical chord; The intersection point is used as the form value point of the piecewise spline curve, and the piecewise spline curve is expressed as a piecewise cubic B-spline function by using the second-order derivative at the form value point. According to the continuity of the first-order derivative of the cubic B-spline function at the form value point, and the first and last segments of the piecewise spline curve are parabolas as boundary conditions, the second-order derivative value at the form value point is determined, and the cubic B-spline function is determined according to the second-order derivative value at the form value point; Sample points are taken on the piecewise spline curve according to the preset step size of the X-axis coordinate component, and the distance from each sample point to the spherical chord is calculated respectively, and the central spherical chord height is equal to the maximum value of the distance.

2. The method according to claim 1, characterized in that The step of determining the intersection of the triangular point cloud grid of the front windshield model and the height reference plane according to the height reference plane and the point cloud information also includes: Traversing the triangular point cloud meshes, determining the number of intersections between each triangular point cloud mesh and the high-speed reference plane, and calculating the product of the Y-axis component of the vertex of each triangular point cloud mesh and the height average value difference; When d1d2<0 and d1d3<0, find the intersection of P1P2, P1P3 and the high-speed reference plane; When d1d2<0 and d2d3<0, find the intersection of P1P2, P2P3 and the high-speed reference plane; When d1d3<0 and d2d3<0, find the intersection of P1P3, P2P3 and the high-speed reference plane; When one of d1, d2, and d3 is zero, the product of the other two is determined. If the product is greater than zero, the intersection is not saved. If the product is less than zero, the intersection is calculated and saved. If the product is equal to zero, the two vertices are saved, where P1, P2, and P3 are the vertices of the triangular point cloud mesh, and d1, d2, and d3 are the differences between P1, P2, and P3 and the average height.

3. The method according to claim 2, characterized in that The step of determining the intersection of the triangular point cloud grid of the front windshield model and the height reference plane according to the height reference plane and the point cloud information also includes: obtaining the X-axis coordinate component of the intersection, and deleting one intersection when the difference between the X-axis coordinate components of the two intersections is less than a preset threshold.

4. The method according to claim 1, characterized in that The preset step size is 0.

01.

5. A device for calculating the central spherical chord height of a vehicle front windshield, characterized in that: It comprises a memory and a processor, wherein the memory comprises a computer program, and when the computer program is run by the processor, the method for calculating the central spherical chord height of the front windshield of the vehicle as claimed in any one of claims 1 to 4 is executed.

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