Method for determining reference points for a coordinate transformation and computer-implemented method for measuring the mechanical stress on a measured object.

Abstract

Method for determining reference points (RP1 to RP4) for a coordinate transformation for a measurement of a mechanical stress on a measured object (1), characterized by the following steps: - Positioning a plurality of measuring points (10.n) on a surface of the object being measured (1) and assigning a unique reference identifier to each positioned measuring point (10.n), - Preliminary measurement of the positioned measuring points (10.n) with the assigned reference identifier before mechanical stress on the object being measured (1) using a predetermined coordinate system (4, 5), - Remeasurement of the positioned measuring points (10.n) with the assigned reference identifier after a mechanical stress on the measuring object (10.n) using the specified coordinate system (4, 5), - Determination of distance changes between measuring points (10.n) with the assigned reference identifier of the preliminary survey and measuring points (10.n) with the same assigned reference identifier of the subsequent survey, and - Determination of those measuring points (10.n) of the preliminary survey and the subsequent survey with a specified distance change between preliminary survey and subsequent survey and - Determination of a reference triangle (17) with reference points (RP1 to RP3) based on three measuring points (10.n) with the specified distance changes - Determination of a further measuring point (10.n) as a fourth reference point (RP4), which has shifted the least relative to the reference points (RP1 to RP3) between the pre-measurement and the post-measurement, such that a solid body is formed with the reference triangle (17) and the fourth reference point (RP4), and - Transformation of the coordinates of the measurement points (10.n) of the subsequent survey into the coordinates of the preliminary survey starting from the four reference points (RP1 to RP4).

Description

[0001] The invention relates to a method for determining reference points for a coordinate transformation for measuring the mechanical stress on a test object. Furthermore, the invention relates to a computer-implemented method for measuring the mechanical stress on a test object.

[0002] In a crash test, information can typically be provided through crash vehicle measurements. For example, geometries of 3D measurement objects, such as vehicle geometries, are recorded before and after a crash test using different measurement methods.

[0003] Typically, this involves the three-dimensional acquisition of coordinates of discrete points. Based on the measurement data, it is possible to determine the deformations of individual areas, sections, and / or structures, particularly vehicle structures and / or vehicle sections, after a crash test. To analyze the measurement data before and after the crash test as effectively as possible, the measurements must be in an identical coordinate system. Using a coordinate transformation, the measurements are converted into a defined vehicle coordinate system. The coordinate transformation significantly influences the measurement result. The results of the post-test measurements vary significantly depending on the chosen transformation method and the selected transformation points, and can lead to inaccurate results. Consequently, the actual crash deformation may differ from the measured or simulated crash deformation.

[0004] The current procedure for transforming post-measurement measurements is based on the use of standardized reference point positions, known as measurement points (also called EP or EP points). Three stable measurement points are used, which experience only minimal deformation during a crash test. These measurement points are defined on the vehicle during the initial measurement and then measured together with the remaining measurement points. The coordinates of the measurement points from the initial measurement are then used in the coordinate transformation for the post-measurement.

[0005] The disadvantage is that the theoretically deformation-stable measurement points actually experience a greater displacement than assumed, and that the spatial distribution of the measurement points on the 3D measurement object, especially a vehicle, is not optimal.

[0006] For the transformation of the post-measurement data, it is common practice to select three reference points and align them using the so-called 3-2-1 method. The selection of reference points depends, for example, on the specific type of impact on the object being measured, such as the vehicle, during the crash test. Such a transformation using the 3-2-1 method offers no way to verify the accuracy of the alignment. Furthermore, errors can occur in the coordinates of the reference points, which can directly lead to errors in the observation points, i.e., the remaining measurement points.

[0007] From DE 10 2022 130 676 A1 a method for determining a deformation of a motor vehicle, an associated motor vehicle with a body surface and an associated system is known.

[0008] From DE 102 12 337 A1 a method for analyzing vehicle deformations is known, in particular vehicle deformations caused by real accidents, in which measuring points are applied to a deformed vehicle and in which the position of the measuring points is measured.

[0009] From EP 4 202 849 A1, a method and a device for detecting damage to a vehicle are known, comprising the steps of: capturing optical data of the vehicle; determining several surface parameters from the optical data; and determining a probability of damage from the several surface parameters for a plurality of points on the vehicle surface.

[0010] DE 10 2019 135 727 A1 discloses a method for determining measuring points on a surface of a workpiece to be measured in order to determine the position and orientation of the surface by determining the position of the measuring points predetermined by the method.

[0011] The invention is based on the objective of providing an improved method for determining reference points for a coordinate transformation for measuring the mechanical stress of a measured object, as well as an improved computer-implemented method for measuring the mechanical stress of a measured object during a crash.

[0012] The first-mentioned problem is solved according to the invention by a method for determining reference points for a coordinate transformation with the features of claim 1. The second-mentioned problem is solved according to the invention by a computer-implemented method for measuring a mechanical stress on a measuring object with the features of claim 7.

[0013] Advantageous embodiments of the invention are the subject of the dependent claims.

[0014] The inventive method for determining reference points for a coordinate transformation for measuring a mechanical stress on a measured object is characterized by the following steps: - Positioning a plurality of measuring points on a surface of the object being measured and assigning a unique reference identifier to each positioned measuring point, - Preliminary measurement of the positioned measuring points with the assigned reference identifier before mechanical stress on the object being measured, using a predefined coordinate system, - Remeasurement of the positioned measuring points with the assigned reference identifier after mechanical stress on the object being measured, using the specified coordinate system, - Determination of distance changes between measuring points with the assigned reference identifier of the preliminary survey and measuring points with the same assigned reference identifier of the subsequent survey, and - Determination of those measuring points of the preliminary survey and the subsequent survey with a specified change in distance between preliminary survey and subsequent survey and - Determination of a reference triangle with reference points based on three measuring points with the specified distance changes, - Determination of a further measuring point as a fourth reference point, which has shifted the least relative to the reference points between the preliminary and subsequent measurements, such that a solid body is formed with the reference triangle and the fourth reference point, and - Transformation of the coordinates of the measurement points of the subsequent survey into the coordinates of the preliminary survey starting from the four reference points.

[0015] The method according to the invention allows a 3D data set, in particular a point cloud, of a 3D measurement object, such as a vehicle, to be displayed and simulated with high accuracy in a coordinate system.

[0016] The invention enables optimized coordinate transformation, particularly for object simulation, especially object measurement, such as crash vehicle measurement. The method is based on the computational determination of reliable reference points that have only minimal deformation after the crash test and exhibit improved spatial distribution. The coordinate transformation is then performed using these determined reference points, for example, with the so-called best-fit method. Preliminary measurement creates a model of the object before mechanical stress. For this purpose, a plurality of measuring points are positioned on the object. During the preliminary measurement, coordinates in the predefined coordinate system are assigned to each measuring point and its associated reference identifier. The predefined coordinate system can, for example, be an object coordinate system.As part of the preliminary measurement, an optional transformation from a machine coordinate system to the specified coordinate system can be performed to compensate for differences between various measurements by the measuring system.

[0017] During the subsequent measurement process, the measuring points of the object are measured after mechanical stress and new coordinates are assigned to each point within the specified coordinate system. Consequently, the subsequent measurement creates a model of the object after mechanical stress. Optionally, a transformation from a machine coordinate system to the specified coordinate system can also be performed to compensate for differences between various measurements taken by the measuring system.

[0018] To investigate the effects of mechanical stress, the coordinates of the measurement points from the post-survey must be transformed into the coordinates of the measurement points from the pre-survey. First, the changes in distance between the measurement points with the assigned reference identifier from the pre-survey and measurement points with the same assigned reference identifier from the post-survey are determined. Then, those measurement points from the pre-survey and post-survey that exhibit a predefined change in distance between the two are identified. A reference triangle is then formed from three measurement points with the predefined change in distance between the pre-survey and post-survey, with these three measurement points serving as the reference points of the reference triangle.Using an additional measurement point as a fourth reference point, a solid is formed with the reference triangle. The measurement point selected as the fourth reference point is the one that has shifted the least relative to the reference points between the initial and subsequent measurements. The resulting solid is a so-called tetrahedron. Finally, the coordinates of the measurement points from the subsequent measurement are transformed into the coordinates of the initial measurement, starting from the four reference points.

[0019] The inventive method allows for a significantly more accurate coordinate transformation of the coordinates of the measuring points from the subsequent survey into the coordinates of the preliminary survey.

[0020] Advantageously, the distances between each measuring point with the assigned reference identifier from the preliminary survey and each measuring point with the same assigned reference identifier from the subsequent survey can be determined using two distance matrices. This enables efficient data processing.

[0021] In one embodiment of the invention, the maximum change in distance between the reference points in the base triangle or the reference triangle can be specified as an input parameter for determining the reference triangle. Alternatively, a minimum change in distance could also be specified.

[0022] In another embodiment, the minimum distance between the reference points in the base triangle or the reference triangle can be specified as an input parameter. Alternatively, a maximum distance could also be specified.

[0023] In another embodiment, the maximum change in distance between the fourth reference point and the reference points of the base triangle or the reference triangle can be specified as an input parameter. Alternatively, a minimum change in distance could also be specified.

[0024] In another embodiment, the minimum distance of the fourth reference point to the reference points of the base triangle or the reference triangle can be specified as an input parameter. Alternatively, a maximum distance could also be specified.

[0025] By adjusting the input parameters, the optimal reference points for measuring the mechanical stress on the object being measured can be determined. This allows for a particularly precise measurement of the stress on the object.

[0026] Computer-implemented method for determining reference points for a coordinate transformation for a measurement of a mechanical stress of a measured object, which is determined using the method according to one of the preceding claims.

[0027] The task is also solved by a computer-implemented method, in particular a simulation method, to determine reference points for a coordinate transformation for measuring a mechanical stress on a measured object.

[0028] Exemplary embodiments of the invention are explained in more detail below with reference to a drawing.

[0029] This shows: Fig. 1. Schematic exploded view of a measuring object in a measuring system for measuring the measuring object and a coordinate system. Fig. 2. Schematically, an abstraction of the measurement object according to Fig. 1 with a plurality of measuring points, Fig. 3. Schematically, the abstraction of the measurement object according to Fig. 2 after an initial local mechanical stress, Fig. 4 schematically the abstraction of the measurement object according to Fig. 2 after a second local mechanical stress, Fig. 5 schematically the abstraction of the measurement object according to Fig. 2 after a third local mechanical stress, Fig. 6 schematically the abstraction of the measurement object according to Fig. 2 after a fourth local mechanical stress, Fig. Figure 7 schematically shows a first stress scenario of the reference model according to Fig. 2, Fig. 8 schematically a second stress scenario of the reference model according to Fig. 2, Fig. 9 schematically a third stress scenario of the reference model according to Fig. 2, Fig. 10. Schematically, the abstraction of the measurement object according to Fig. 1 with a first determined reference coordinate system, and Fig. 11 schematically the abstraction of the measurement object according to Fig. 1 with a second determined reference coordinate system.

[0030] Corresponding parts are marked with the same reference symbols in all figures.

[0031] Fig. Figure 1 schematically shows an exploded view of a measurement object 1 in a measuring system 2. The measurement object 1 is, for example, a three-dimensional object 1, in particular a vehicle 3 to be measured and / or simulated. The measurement object 1 is shown in its actual shape and contour.

[0032] The measuring system 2 comprises at least one electronic measuring unit 2.1 and a computer unit 2.2, which is coupled to the measuring unit 2.1, for example, a distance meter, an optical measuring unit, or another suitable measuring unit for measuring distances and lengths. The computer unit 2.2 is coupled to the electronic measuring unit(s) 2.1 via a signal connection, in particular wirelessly and / or via a wired connection. The computer unit 2.2 is, for example, a computer, a tablet, or another suitable data processing unit.

[0033] The measured object 1 has an associated object coordinate system 4 with an associated y-object coordinate 4y, an associated x-object coordinate 4x and a z-object coordinate 4z.

[0034] The measuring system 2 has an associated measuring coordinate system 5 with an associated y-measuring coordinate 5y, an associated x-measuring coordinate 5x and a z-measuring coordinate 5z.

[0035] To align and measure the object 1, in particular to compare two measurements of the object 1, the measuring points 10.1 to 10.n are transformed from the measurement coordinate system into the object coordinate system.

[0036] The procedure described below serves to determine reference points (RP1 to RP4) for a coordinate transformation for measuring the mechanical stress on a measured object (1), which is used as an example in Fig. 7 and Fig. 8 is shown.

[0037] The current procedure for aligning a crash remeasurement is based on the use of standardized positions of reference points RP1 to RP4, the so-called calibration points EP1 to EP4 (shown in Fig. 2) For the interpretation of the measurement results, a reliable transformation into the object coordinate system 4, for example a vehicle coordinate system, as in Fig. 1 shown, essential.

[0038] New requirements, such as high-speed and truck tests, have shown that the theoretically deformation-stable measurement points EP1 to EP4 experience higher loads in practice than previously assumed. A change in the position of measurement points EP1 to EP4 after a crash has been demonstrated. The current distribution of measurement points EP1 to EP4 is not optimal, as they lie within a single plane and therefore do not adequately represent the vehicle's spatial distribution.

[0039] The aim of the invention is to measure measuring points 10.1 to 10.n, as in Fig. Figure 2 illustrates how a specific abstraction procedure is used to determine which measurement points EP1 to EP4 correspond to the basic concept. This means identifying those measurement points 10.1 to 10.n that are deformation-stable and whose position has demonstrably not changed, or has changed only minimally, after a crash test. The abstraction procedure is described in more detail below.

[0040] Since the measurement points 10.1 to 10.n determined using this abstraction method correspond to the reference points EP1 to EP4, they can be used for a coordinate transformation. The abstraction method provides for the future reference points EP1 to EP4 to be determined individually for each crash test, based on an algorithm described below.

[0041] For example, measurements using a 3D scanning system with a large number of measurement points 10.1 to 10.n can serve as a basis.

[0042] Fig. Figure 2 shows an abstraction 10 (hereinafter referred to as reference model 10) of the measured object 1 according to Fig. 1 with a plurality of measurement points 10.1 to 10.n. The reference model 10 is, for example, an abstract or schematic model of the measurement object 1, such as a rectilinear contour model of the measurement object 1. A high number of available measurement points 10.1 to 10.n increases the probability of determining deformation-stable points as measurement points EP1 to EP4 and thus reference points RP1 to RP4.

[0043] Depending on the object to be measured 1, for example 300 to 500 measuring points 10.1 to 10.n can be manually defined as reference points RP.n on the entire object surface during scanning.

[0044] During the application of the new method, when measuring, for example, a vehicle as measurement object 1, care is taken to place additional reference points RP.n in areas that are expected to experience little deformation after a crash test. The coordinates of the reference points RP.n in the scan form the basis for the subsequent evaluation with the algorithm.

[0045] The algorithm requires certain conditions that allow it to identify the desired deformation-stable points. Firstly, points must be filtered out whose positions can be assumed to remain constant after the crash test. Secondly, care must be taken to ensure the best possible spatial network distribution.

[0046] This can be achieved by defining specific input parameters for the algorithm. For example, criteria can be specified to filter out the reference points RP.n on the vehicle surface that remained unchanged after the crash. This should make it possible in the future to align remeasurements using reliable reference points EP.n, thereby increasing the accuracy of the collected measurement data.

[0047] The procedure is explained below.

[0048] The measuring points 10.1 to 10.n are, for example, markers. The measuring unit 2.1 is configured to measure the position and / or the relative positions of each measuring point 10.1 to 10.n in a preliminary survey and / or to assign them to the respective measuring point 10.1 to 10.n. The measuring points 10.1 to 10.n form a point cloud 11 on a circumferential surface (= lateral surface and base surface) of the reference model 10.

[0049] Due to its construction, structure and material, the reference model 10 can exhibit different deformation ranges 12.1 to 12.2.

[0050] For example, a deformable vehicle outer skin forms a first deformation zone 12.1 and a rigid floor body forms a second deformation zone 12.2. In a possible accident, the first deformation zone 12.1 is more deformed than the second deformation zone 12.2.

[0051] The reference model 10 can, for example, be a thin sheet metal shell as the first deformation zone 12.1 and a robustly welded steel frame as the second deformation zone 12.2. The sheet metal shell can, for example, be welded onto this steel frame. The measuring points 10.1 to 10.n in the second deformation zone 12.2, in the steel frame, generally do not experience any deformation, only the measuring points 10.1 to 10.n in the first deformation zone 12.1, in the sheet metal shell.

[0052] The guiding principle of coordinate transformation is based on calculating distances between the individual reference points RP1 to RP.n within a measurement. The subsequent comparison of these distances from the initial and subsequent measurements should reveal which points or point combinations can still be considered stable after the crash test.

[0053] Fig. Figures 3 to 6 show the reference model 10 according to Fig. 2. after various local mechanical stresses, for example after an accident, an impact or the like.

[0054] Fig. Figure 3 shows the reference model 10, which, following an accident or mechanical stress, is partially deformed in the first deformation zone 12.1, particularly in a roof area. As a result, measuring points 10.1 to 10.3 and, if applicable, further measuring points 10.n are displaced in the affected areas, while measuring points 10.6 to 10.8 and, if applicable, further measuring points 10.n in the second deformation zone 12.2, which was not deformed at all or only slightly, are displaced or remain displaced.

[0055] Fig. Figure 4 shows the reference model 10, which is partially deformed in the first deformation area 12.1, particularly in a front area, after an accident or mechanical stress.

[0056] Fig. Figure 5 shows the reference model 10, which, after an accident or mechanical stress, is partially deformed in the first deformation area 12.1, particularly in a front area and a rear area.

[0057] Fig. Figure 6 shows the reference model 10, which, after an accident or mechanical stress, is partially deformed in the first deformation area 12.1, in particular in a roof area, a front area and a rear area.

[0058] Typically, three fixed measurement points EP1 to EP3 are specified in the second deformation area 12.2, which is not deformed at all or only very slightly, for example in the area of ​​a sill or in the vehicle floor area.

[0059] The invention is based on the consideration that it depends on the load case and the location of the mechanical stress.

[0060] Fig. Figures 7 to 9 show different stress scenarios 13.1 to 13.3 and the previous method of using fixed measurement points EP1 to EP9 and their weighting to reduce these measurement points EP1 to EP12 to three fixed measurement points EP1 to EP3.

[0061] All three Fig. Figures 7 to 9 show the measurement object 1 with several predefined measurement points EP1 to EP9, which can be weighted differently depending on the stress scenario 13.1 to 13.3, in particular according to the so-called 3-2-1 method of weighting the object coordinates 4x, 4y, 4z at three fixed of several predefined measurement points EP1 to EP12:

[0062] Fig. Figure 7 shows the measuring object 1 after a frontal impact 14 on the left, in which the right rear measuring point EP6 remains stable or fixed or is least displaced and the left front measuring point EP1 is most displaced compared to a prior measurement due to the deformation.

[0063] To determine the object coordinate system 4, the y-object coordinate 4y, the z-object coordinate 4z and the x-object coordinate 4x are weighted at the measurement point EP6 as a so-called full pass point; in particular, the measurement point EP6 receives the coordinates (0,0,0) because there was no or only a slight displacement.

[0064] The right front measurement point EP4 is shifted less in the x-direction than the left front measurement point EP1. Therefore, measurement point EP4 is weighted, for example, only in the y-object coordinate 4y and the z-object coordinate 4z, and in particular, it is weighted less. Similarly, the left rear measurement point EP3 is weighted, for example, only in the z-coordinate 6z, and in particular, it is weighted less than measurement points EP1 and EP4.

[0065] Fig. Figure 8 shows the measuring object 1 after a further frontal impact 15 on the left with a slight rollover, in which the right rear measuring point EP8 remains stable or fixed or is least displaced and the left front measuring point EP1 is most displaced compared to a previous measurement due to the deformation.

[0066] To determine the object coordinate system 4, the y-object coordinate 4y, the z-object coordinate 4z and the x-object coordinate 4x are weighted at the measurement point EP8 as a so-called full pass point; in particular, the measurement point EP8 receives the coordinates (0,0,0) because there was no or only a slight displacement.

[0067] The measurement point EP7 is weighted with respect to the y-object coordinate 4y and the z-object coordinate 4z. The upper measurement point EP9 is weighted with respect to the z-object coordinate 4z.

[0068] Fig. Figure 8 shows the measuring object 1 after a side impact 16, in which the three measuring points EP10, EP11, EP12 on the opposite side remain stable or fixed or are at least displaced compared to a pre-measurement due to the deformation on the other side of the vehicle.

[0069] To determine the object coordinate system 4, the y-object coordinate 4y, the z-object coordinate 4z and the x-object coordinate 4x are weighted at the right front measurement point EP10 as a so-called full pass point; in particular, the measurement point EP10 receives the coordinates (0,0,0) because there was no or only a slight displacement.

[0070] The right rear measurement point EP12 is weighted with respect to the y-object coordinate 4y and the z-object coordinate 4z. The middle measurement point EP11 is weighted with respect to the y-object coordinate 4y.

[0071] This previous weighted determination of three fixed measurement points EP1 to EP3 from the several measurement points EP1 to EP12 can lead to errors, especially since these lie on one plane.

[0072] The method according to the invention is based on the computational determination of four reliable reference points RP1 to RP4, which deformed only minimally after the crash test and exhibit a better spatial distribution. Using these four determined reference points RP1 to RP4, the coordinate transformation is then performed using the so-called best-fit method instead of the known 3-2-1 method. The best-fit method means that all selected measurement points 10.1 to 10.n are considered full-fit points for calculating the spatial similarity transformation, and no separate weighting of the individual coordinate axes is carried out.

[0073] The method also provides for performing the coordinate transformation with an additional fourth reference point, RP4, instead of the minimum required three reference points RP1 to RP3. This additional reference point RP4 defines a solid body, which, due to the improved spatial distribution of the transformation points on the measurement object 1, the vehicle, ensures greater transformation stability.

[0074] The invention therefore provides to determine four measuring points 10.1 to 10.n as four reference points RP 1 to RP4 for a coordinate transformation.

[0075] In order to determine an accident or other mechanical stress on the reference model 10, the invention therefore provides to identify four stable measuring points 10.1 to 10.n as reference points RP1 to RP4 after a mechanical stress. For this purpose, the information from the measured point clouds of the pre-measurement and the post-measurement is used.

[0076] As well as Fig. 10 as well Fig. Figures 11 each schematically show the reference model 10 of the measurement object 1 according to Fig. 1 with a reference coordinate system 6 of the reference model 10, wherein four reference points RP1 to RP4 are determined based on several determined stable measurement points 10.1 to 10.n. Starting from the four reference points RP1 to RP4, the coordinates of the measurement points 10.1 to 10.n from the subsequent measurement are then transformed into the coordinates of the measurement points 10.1 to 10.n of the subsequent measurement.

[0077] The inventive method for determining reference points RP for a coordinate transformation is based on a 3D data set, in particular the point cloud 11 consisting of measurement points 10.1 to 10.n, which are distributed on a circumferential surface of the reference model 10, and which are or have been simulated, in particular measured at various events, in particular pre-measured and post-measured.

[0078] The following steps are carried out: - Positioning the majority of measuring points 10.1 to 10.n on a surface of the 3D measuring object 1 or the reference model 10, as in Fig. 3 to 6, shown using a predefined coordinate system, in particular the object coordinate system 4 or the measurement coordinate system 5, and assigning a unique reference identifier (= own ID number) to each positioned measurement point 10.1 to 10.n, - Preliminary measurement of the positioned measuring points 10.1 to 10.n with the assigned reference identifier before mechanical stress on the reference model 10 or the simulated 3D measuring object 1 using the specified coordinate system with three stable measuring points 10.1 to 10.n, - Remeasurement of the positioned measuring points 10.1 to 10.n with the assigned reference identifier after a mechanical stress on the reference model 10 or the simulated 3D measuring object 1 using the specified coordinate system, - Feeding the point cloud (of measurement points 10.1 to 10.n with assigned reference identifier = ID identifier) ​​into the algorithm according to the invention, - Determination of the distances a.1 to an between the measuring points 10.1 to 10.n with the assigned reference identifier of the pre-measurement and the measuring points 10.1 to 10.n with the same assigned reference identifier of the post-measurement (for example, by subtracting two matrices and determining a distance change matrix which contains the changes in the pairwise measured distances an between the measuring points 10.1 to 10.n as a result of the crash test; in other words: the matrices contain the pairwise measured distances between the measuring points 10.1 to 10.n of a point cloud), and - Determination of those measuring points 10.1 to 10.n of the preliminary survey and the subsequent survey with the smallest changes in distance between the preliminary survey and the subsequent survey, and - Determination of a reference triangle 17 (also called base triangle) with three reference points RP1 to RP3 based on the three measuring points 10.3 with the smallest changes in distance and a fourth measuring point 10.4, which has shifted the least relative to the three measuring points 10.1 to 10.3 of the reference triangle 17 between the initial and subsequent measurements and which forms a fourth reference point RP4. For example, possible three-point combinations are determined based on two input parameters and a base triangle is constructed. The first input parameter for calculating the base triangle can, for example, be the minimum distance between the vertices. The second input parameter specifies, for example, the maximum permissible change in the distance between the vertices of the triangle. The accuracy of the base or reference triangle 17 can be set via this input parameter. - Determination of a reference tetrahedron with the four reference points RP1 to RP4 as reference measurement points based on the determined reference triangle 17 and the determined fourth measurement point 10.4, and - Transformation of the coordinates of the measurement points of the subsequent survey into the coordinates of the preliminary survey starting from the four reference points.

[0079] With the additional fourth reference point RP4, which is only minimally shifted relative to the vertices of the triangle, a solid, a so-called tetrahedron, can be constructed. The tetrahedron allows for a better spatial distribution of the transformation points and greater transformation stability. Possible four-point combinations are determined by combining the triangle vertices with the fourth reference point RP4. Filtering the tetrahedra requires the input of two additional parameters. These are selected analogously to the input parameters of the base triangle. The size of the tetrahedron is defined by the minimum distance of the fourth reference point RP4 to each of the triangle vertices. The accuracy of the tetrahedron can be adjusted by entering the maximum change in the distance between the individual triangle vertices and the fourth reference point RP4.After entering the parameters, the calculation of possible four-point combinations follows.

[0080] Next, one of the identified and proposed tetrahedra is selected. The coordinate transformation of the subsequent survey is performed using the points of the selected four-point combination—essentially the vertices of the tetrahedron—with the best-fit method. The coordinates of these four reference points, RP1 to RP4, in the subsequent survey are overwritten with the coordinates of the four reference points, RP1 to RP4, from the initial survey.

[0081] In summary, the procedure comprises the following steps: - Determine the reference identifier (ID number) of measuring points 10.1 to 10.n from pre- and post-survey measurements, - Check the reference identifier matches, - Importing the point clouds from the pre- and post-survey with identical reference identifiers and feeding them into the algorithm for reference point determination, - Determining the distance matrices from the point clouds of the pre- and post-survey, - Calculation of the distance change matrix from the distance matrices, - Parameter input for distance filtering to determine the base triangles, - Determination of the base triangles using the parameters, - Parameter input for distance filtering to determine the tetrahedra, - Determination of the tetrahedra based on the parameters, - Selection of a tetrahedron, - Coordinate transformation via the vertices (= reference points RP1 to RP4) of the selected tetrahedron.

[0082] The algorithm for determining the reference point is based, for example, on four input files. These input files include, for example, the two point clouds from the pre-survey and post-survey, and two area datasets from the pre- and post-survey.

[0083] The point clouds also include the reference identifiers (ID numbers) and the three-dimensional coordinates of measurement points 10.1 to 10.n. They can be loaded into the program, for example, as a 0132.csv file or a .txt file. The program then checks that the reference identifiers (ID numbers) of measurement points 10.1 to 10.n (also called reference points) from both point clouds are identical.

[0084] The three-dimensional coordinates differ. Analysis would be possible solely by displaying the point clouds. For improved analysis and visualization, the measured surface geometry can also be imported as an ".stl" file. The ".stl" format represents the surface of the measured object 1 using a multitude of small polygons (line segments).

[0085] The invention enables an optimized coordinate transformation, particularly for object simulation, especially object measurement, such as crash vehicle measurement. The method is based on the computational determination of four reliable reference points RP1 to RP4, which deform only minimally after the crash test and exhibit a better spatial distribution. Using these determined reference points RP1 to RP4 of the tetrahedron, the coordinate transformation is then performed using the so-called best-fit method.

[0086] The four reference points RP1 to RP4 define a solid body, which, due to the better spatial distribution of the transformation points, ensures higher transformation stability.

[0087] In other words, the procedure uses information from a measured point cloud 11. Each measurement point 10.n is assigned its own identifier or ID number (identification number). For the subsequent calculation, identical measurement points 10.n from the pre-survey and the post-survey must be assigned identical ID numbers. The measurement points 10.n that form the point cloud 11, from both the pre-survey and the post-survey, in particular their measured values, position values, distance values, or the like, are read into a program in which the calculation algorithm required for coordinate transformation is implemented.

[0088] Subsequently, the distances between each measurement point 10.n and each measurement point 10.n in the point cloud 11 of the preliminary survey and in the point cloud 11 of the subsequent survey are determined, for example, in the form of two distance matrices. A distance change matrix is ​​then obtained by subtracting these two distance matrices.

[0089] The sections with the smallest changes in distance between the initial and subsequent measurements are filtered using input parameters. Based on these parameters, possible three-point combinations are then determined, and a base triangle is defined and designated as reference triangle 17. Using at least one additional measurement point 10.4 (in this case, a fourth point), which has shifted only minimally relative to the triangle points (reference points RP1 to RP3) of reference triangle 17, a solid (for example, a tetrahedron) is determined. Possible multi-point combinations are then determined by combining the triangle points with the additional measurement point 10.4. To determine the additional measurement point 10.4 as the fourth measurement point EP4, additional parameters, in particular weighting parameters, limit values, or the like, can be specified and taken into account.

[0090] Subsequently, one of the software-determined multi-point combinations of the four measuring points 10.1 to 10.n is selected, which serve as reference points RP1 to RP4 for the coordinate transformation.

[0091] The coordinate transformation of the resurvey is carried out using these determined reference points RP1 to RP4 of the selected multi-point combination, applying the best-fit method.

[0092] This method enables the optimization of coordinate transformation in crash vehicle measurement and the reliable determination of reference points RP1 to RP4. This simplifies and improves the quality of development processes, particularly vehicle development processes, and / or simulations such as deformation analyses, crash simulations, etc., making them more accurate and safer.

[0093] The method is designed as a computer-implemented method, in particular as a digital simulation method for measuring the mechanical stress on the object 1 during a crash, using the determined reference coordinate system 6.

[0094] The measuring points 10.1 to 10.n, the point cloud 11 and / or the calibration points EP1 to EP12 can also be specified manually. The reference points RP1 to RP4 are only determined during the subsequent measurement, i.e., after mechanical stress has been applied to the reference model 10 or the object being measured 1, as described above.

[0095] For example, the procedure for alignment and as reference points RP1 to RP4 specifies measuring points 10.1 which are located in the fixed second deformation area 12.2, for example in the steel frame.

[0096] The method can also, for example in the case of a pure frontal impact, detect and output measuring points 10.1 to 10.n with high accuracy and little deformation outside the fixed second deformation area 12.2; this is particularly dependent on the direction of action or impact.

[0097] In contrast, in the event of total loss of the first deformation area 12.1, for example the sheet metal body, only measuring points 10.n from the second deformation area 12.2, the steel frame, are determined and output as reference points RP1 to RP4.

[0098] This method allows for the determination of reliable alignment points for subsequent surveying by identifying four reference points, RP1 to RP4, for coordinate transformation. Furthermore, different orientations of the reference model 10 can be visualized and compared. Deformation analyses can also be performed on the reference model 10. The comparison of orientations can be easily and reliably demonstrated using various load cases.

Claims

[1] Method for determining reference points (RP1 to RP4) for a coordinate transformation for a measurement of a mechanical stress on a measured object (1), characterized by the following steps: - Positioning a plurality of measuring points (10.n) on a surface of the object being measured (1) and assigning a unique reference identifier to each positioned measuring point (10.n), - Preliminary measurement of the positioned measuring points (10.n) with the assigned reference identifier before mechanical stress on the object being measured (1) using a predetermined coordinate system (4, 5), - Remeasurement of the positioned measuring points (10.n) with the assigned reference identifier after a mechanical stress on the measuring object (10.n) using the specified coordinate system (4, 5), - Determination of distance changes between measuring points (10.n) with the assigned reference identifier of the preliminary survey and measuring points (10.n) with the same assigned reference identifier of the subsequent survey, and - Determination of those measuring points (10.n) of the preliminary survey and the subsequent survey with a specified distance change between preliminary survey and subsequent survey and - Determination of a reference triangle (17) with reference points (RP1 to RP3) based on three measuring points (10.n) with the specified distance changes - Determination of a further measuring point (10.n) as a fourth reference point (RP4), which has shifted the least relative to the reference points (RP1 to RP3) between the pre-measurement and the post-measurement, such that a solid body is formed with the reference triangle (17) and the fourth reference point (RP4), and - Transformation of the coordinates of the measurement points (10.n) of the subsequent survey into the coordinates of the preliminary survey starting from the four reference points (RP1 to RP4). [2] Method according to claim 1, characterized by , that distances (an) between the respective measuring point (10.n) with the assigned reference identifier of the preliminary survey and the respective measuring point (19.n) with the same assigned reference identifier of the subsequent survey are determined using two distance matrices. [3] Method according to claim 1 or 2, characterized by , that the maximum change in distance between the reference points (RP1 to RP3) in the base triangle or the reference triangle (17) is specified as an input parameter for determining the reference triangle (17). [4] Method according to claim 1 or 2, characterized by , that the minimum distance of the reference points (RP1 to RP3) in the base triangle or the reference triangle (17) is specified as an input parameter. [5] Method according to claim 1 or 2, characterized by , that the maximum change in distance of the fourth reference point (RP4) to the reference points (RP1 to RP3) of the base triangle or the reference triangle (17) is specified as an input parameter. [6] Method according to claim 1 or 2, characterized by , that the minimum distance of the fourth reference point (RP4) to the reference points (RP1 to RP3) of the base triangle or the reference triangle (17) is specified as an input parameter. [7] Computer-implemented method for determining reference points (RP1 to RP4) for a coordinate transformation for a measurement of a mechanical stress of a measuring object (1) which is determined by a method according to one of the preceding claims.

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