Calibration Module and Its Usage Method

Abstract

The present invention relates to the technical field of reflection detection, and provides a calibration module and a method for using the same. The calibration module includes: a plurality of observation planes, at least two of the planes where the plurality of observation planes are located intersect, and there is a definite spatial position relationship between the plurality of observation planes; an observation area is provided on each observation plane, and each observation area has a corresponding calibrated BRDF value. By providing a calibration module in the shape of a polyhedron, the present invention improves the accuracy of measuring the attitude of the calibration module and the incident angle of the light source, and further improves the accuracy of measuring the BRDF characteristics of the surface of the object to be measured.

Description

Technical Field

[0001] The present invention relates to the technical field of reflection detection, and particularly to a calibration module and a method for using the same. Background Art

[0002] When detecting the optical properties of the surface of an object to be measured, a standard plate is often used as a calibrator for calibration. However, it is difficult for the standard plate to well characterize the optical properties of the object to be measured, resulting in low accuracy in detecting the optical properties of the surface of the object to be measured. Summary of the Invention

[0003] The present invention provides a calibration module and a method for using the same, which are used to solve or improve the problem of low detection accuracy when detecting the optical properties of the surface of an object to be measured by using a standard plate.

[0004] The present invention provides a calibration module, including: a plurality of observation planes, at least two of the plurality of observation planes intersect, and there is a definite relative spatial position relationship between the plurality of observation planes; an observation area is provided on each of the observation planes, and each of the observation areas has a corresponding calibrated bidirectional reflection spatial distribution function value.

[0005] According to the calibration module provided by the present invention, the shape of the observation area includes: an equilateral triangle, a square, a regular pentagon, a regular hexagon and a regular octagon.

[0006] According to the calibration module provided by the present invention, the observation area is divided into a plurality of assignment areas, and the bidirectional reflection spatial distribution function values of any two of the assignment areas in the same observation area are different.

[0007] According to the calibration module provided by the present invention, the plurality of observation planes enclose a closed cavity.

[0008] The present invention also provides a method for using the calibration module as described above, including:

[0009] Placing the calibration module in the light source environment where the object to be measured is located; obtaining the first image information of the calibration module and the second image information of the object to be measured;

[0010] Based on the first image information, determining the attitude of the calibration module and the incident angle of the light source; based on the second image information, determining the first radiance value of the surface of interest on the object to be measured;

[0011] According to the first radiance value, matching the surface of interest with the observation area, and determining the BRDF characteristic of the surface of interest in the light source environment.

[0012] A method for using a calibration module provided by the present invention, which determines the attitude of the calibration module and the incident angle of the light source based on the first image information, includes:

[0013] Perform ellipse fitting on the vertices of one of the observation regions on the first image information to obtain a fitted ellipse;

[0014] Obtain the center coordinates, major axis length, and minor axis length of the fitted ellipse;

[0015] Based on the center coordinates, major axis length, and minor axis length of the fitted ellipse, determine the orientation of the observation plane corresponding to the fitted ellipse to obtain the attitude of the calibration module.

[0016] A method for using a calibration module provided by the present invention, which determines the attitude of the calibration module and the incident angle of the light source based on the first image information, further includes:

[0017] Based on the first image information, determine the second radiance value and irradiance value corresponding to each observation region on the first image information;

[0018] According to the irradiance value, determine the length of the normal vector of the plane where the corresponding observation region is located;

[0019] Synthesize the normal vectors corresponding to multiple observation regions to obtain the incident angle of the light source.

[0020] A method for using a calibration module provided by the present invention, which matches the surface of interest with the observation region according to the first radiance value and determines the BRDF characteristic of the surface of interest in the light source environment, includes:

[0021] Match the first radiance value with multiple second radiance values to determine the observation region corresponding to the surface of interest;

[0022] Based on the BRDF characteristic of the observation region in the light source environment, determine the BRDF characteristic of the surface of interest in the light source environment.

[0023] A method for using a calibration module provided by the present invention, which determines the attitude of the calibration module and the incident angle of the light source based on the first image information, further includes:

[0024] Obtain the echo time and echo intensity of each observation region of the calibration module;

[0025] Determine the attitude of the calibration module according to the echo time and echo intensity.

[0026] The calibration module provided by the present invention and its usage method form a three-dimensional calibration module by setting multiple observation planes, and each observation plane has a definite relative spatial position relationship. It can be understood that the included angle between the normal vectors of any two observation planes is a preset value. As long as the orientations of any two intersecting observation planes are known, the attitude of the calibration module can be determined. At the same time, each observation area has been pre-assigned and calibrated, so that each observation area has a known BRDF value. Therefore, when using the calibration module to measure the BRDF characteristics of the surface of the object to be measured, the calibration module is placed in the same light source environment as the object to be measured. By calculating the attitude of the calibration module and the incident angle of the light source, according to the known BRDF values of each observation area, the BRDF characteristics corresponding to each observation area in this light source environment can be obtained. By collecting the radiance of the surface of the object to be measured, the observation area close to the radiance of the object to be measured is traversed in multiple observation areas, that is, the surface of the object to be measured is matched with the observation area, and then the BRDF characteristics of the surface of the object to be measured under this light source can be obtained. By setting a three-dimensional calibration module, the attitude of the calibration module and the incident angle of the light source can be measured from multiple angles, improving the accuracy of measuring the attitude of the calibration module and the incident angle of the light source, and further improving the accuracy of measuring the BRDF characteristics of the surface of the object to be measured, avoiding the visual blind area and improving the accuracy and precision of the measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1 is a schematic diagram of the principle of attitude measurement of the calibration module provided by the present invention;

[0029] Figure 2 is a schematic diagram of the principle of measuring the incident angle of the light source provided by the present invention;

[0030] Figure 3 is a schematic diagram of the layout of the calibration module and the object to be measured provided by the present invention;

[0031] Figure 4 is a schematic flowchart of the usage method of the calibration module provided by the present invention;

[0032] REFERENCE SIGNS:

[0033] 1: calibration module; 2: object to be measured; 3: camera; 4: lidar; 5: circular track. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the protection scope of the present invention.

[0035] The following will describe Figures 1 to 4 the calibration module provided by the present invention and its usage method.

[0036] As Figure 1 and Figure 2 shown, the calibration module shown in this embodiment includes: a plurality of observation planes, at least two of the plurality of observation planes intersect, and there is a definite spatial position relationship between the plurality of observation planes; an observation area is provided on each observation plane, and each observation area has a corresponding calibrated BRDF value.

[0037] Specifically, for the calibration module 1 shown in this embodiment, by setting a plurality of observation planes, the plurality of observation planes form a three-dimensional calibration module, and there is a definite relative spatial position relationship between each observation plane. It can be understood that the included angle between the normal vectors of any two observation planes is a preset value. As long as the orientations of any two intersecting observation planes are known, the attitude of the calibration module can be determined; at the same time, each observation area has been pre-assigned and calibrated so that each observation area has a known BRDF value. Thus, when using the calibration module to measure the BRDF characteristics of the surface of the object to be measured, the calibration module 1 is placed in the same light source environment as the object to be measured 2. By calculating the attitude of the calibration module and the incident angle of the light source, based on the known BRDF values of each observation area, the BRDF characteristics corresponding to each observation area in this light source environment can be obtained. By collecting the radiance of the surface of the object to be measured 2, the observation areas close to the radiance of the object to be measured are traversed within a plurality of observation areas, that is, the surface of the object to be measured is matched with the observation areas, and then the BRDF characteristics of the surface of the object to be measured under this light source are obtained; by setting the calibration module 1 in a three-dimensional shape, the attitude of the calibration module 1 and the incident angle of the light source can be measured from multiple angles, improving the accuracy of measuring the attitude of the calibration module 1 and the incident angle of the light source, and further improving the accuracy of measuring the BRDF characteristics of the surface of the object to be measured 2, while avoiding the visual field blind area and improving the measurement accuracy and accuracy.

[0038] It should be noted that BRDF refers to the Bidirectional Reflectance Distribution Function (abbreviated as BRDF); given the orientations of any two intersecting viewing planes in the calibration module 1, the specific method for determining the attitude of the calibration module 1 will be described later.

[0039] Among them, in order to improve the detection accuracy and efficiency of the BRDF characteristics of the surface of the object to be measured 2, a calibration module 1 similar in shape to the object to be measured 2 can be 3D printed according to the contour of the object to be measured 2, and each viewing area is assigned after printing.

[0040] In some embodiments, as Figure 1 shown, the shapes of the viewing areas shown in this embodiment include: equilateral triangle, square, regular pentagon, regular hexagon, and regular octagon.

[0041] Specifically, one viewing area is set on each viewing plane. By setting the viewing area as a regular polygon, the viewing area can reflect light evenly, thereby improving the calibration accuracy of the calibration module 1.

[0042] Among them, the shape of the viewing area is not limited to a regular polygon and can also be an irregular polygon; the number of viewing areas in the shape of a regular polygon is less than or equal to the number of viewing planes; setting the shape of the viewing area as a regular polygon is beneficial to determining the attitude of the calibration module 1, which will be specifically described later.

[0043] In some embodiments, a plurality of standard areas are divided in the viewing area, and the plurality of standard areas have at least two BRDF characteristics.

[0044] Specifically, on the plurality of standard areas in the same viewing area, each standard area is assigned a BRDF value. By setting at least two BRDF values, at least two BRDF characteristics are provided in the same viewing area, which is equivalent to increasing the number of viewing areas, increasing the matchable range of the surface of the object to be measured 2, and improving the versatility of the calibration module 1.

[0045] In some embodiments, as Figure 1 shown, the plurality of viewing planes shown in this embodiment enclose a closed cavity. Correspondingly, the calibration module 1 has a polyhedron structure, so that light can be irradiated onto the calibration module 1 from any angle, and the calibration module 1 can generate reflected light, avoiding an irradiation blind area.

[0046] Among them, the shape of the calibration module 1 can be set to be the same as that of an Archimedean polyhedron.

[0047] As Figure 4As shown in the figure, the present invention also provides a method for using a calibration module, including: step 410, step 420, and step 430.

[0048] Step 410: Place the calibration module in the light source environment where the object to be measured is located; obtain the first image information of the calibration module and the second image information of the object to be measured.

[0049] By placing the calibration module and the object to be measured in the same light source environment, the BRDF characteristics of the object to be measured in this light source environment can be obtained with the help of the calibration module.

[0050] Among them, since the BRDF characteristics depend on the incident angle of the light source, and when the spatial range of the light source environment is small, for example, when measuring in an indoor environment with a fluorescent lamp as the light source, if the distance between the calibration module and the object to be measured is large, the incident angle of the light irradiating on the calibration module is different from the incident angle of the light irradiating on the object to be measured. At this time, the credibility of the BRDF characteristics of the object to be measured obtained through the calibration module is low; therefore, the calibration module needs to be set close to the object to be measured.

[0051] When the spatial range of the light source environment is large, for example, when measuring in an open outdoor environment with natural light as the light source, the distance between the calibration module and the object to be measured has little influence on the incident angle of the light source at this time, and the distance between the calibration module and the object to be measured can be appropriately increased.

[0052] The first image information and the second image information can be obtained by a camera.

[0053] Step 420: Based on the first image information, determine the attitude of the calibration module and the incident angle of the light source; based on the second image information, determine the first radiance value of the surface of interest on the object to be measured.

[0054] Among them, in step 420, the method for determining the attitude of the calibration module includes: step 421, step 422, and step 423.

[0055] Step 421: Perform elliptical fitting on the vertices of one of the observation regions on the first image information to obtain a fitted ellipse.

[0056] Specifically, the first image information collected by the camera is a planar image, and the calibration module is in the shape of a polyhedron. Then the planar image is the projection view of the calibration module. Therefore, the shape of each observation region on the planar image is not the true shape of the observation region, that is, the shape of the observation region has changed. According to the degree of change in the shape of the observation region, the orientation of the observation region relative to the camera can be indirectly calculated.

[0057] As described above, the observation region is set as a regular polygon, which is convenient for fitting the vertices of the regular polygon.

[0058] First, establish a coordinate system as shown in Figure 1 . In this coordinate system, point O is the center of the calibration module. The line where the Z-axis lies is the connection line between point O and the camera. The X-axis is parallel to the horizontal plane, the Y-axis is perpendicular to the X-axis, and the Z-axis is perpendicular to the X-Y plane.

[0059] Among them, the connection line between the center of each observation area and the center of the calibration module is perpendicular to the plane where the observation area is located.

[0060] Perform elliptical fitting on each vertex of one of the observation areas. The contour of the fitted ellipse is shown by the center dash line in Figure 1 . The expression of the fitted ellipse in this coordinate system is:

[0061] ax 2 +2bxy + cy 2 +2dx + 2fy + g = 0

[0062] where a, b, c, d, f, and g are all constants.

[0063] Step 422: Obtain the center coordinates, major axis length, and minor axis length of the fitted ellipse.

[0064] According to each constant in the above expression, calculate the center coordinates (x 0 , y 0 ) of the fitted ellipse. Thus, the vector formed by the center of the fitted ellipse and point O is perpendicular to the plane where the fitted ellipse is located, that is, this vector is the normal vector.

[0065] Among them, the calculation formula for x 0 is:

[0066]

[0067] The calculation formula for y 0 is:

[0068]

[0069] According to each constant in the above expression, calculate the lengths of the major axis and minor axis of the fitted ellipse respectively.

[0070] The calculation formula for the major axis a' is:

[0071]

[0072] The calculation formula for the minor axis b' is:

[0073]

[0074] Step 423: Based on the center coordinates, major axis length, and minor axis length of the fitted ellipse, determine the orientation of the observation plane corresponding to the fitted ellipse to obtain the attitude of the calibration module.

[0075] If the observation plane is facing the camera directly, that is, the normal vector of the observation plane coincides with the Z-axis, then the circumcircle corresponding to the observation area is the fitted ellipse. When the observation plane is deflected, the major axis and minor axis of the fitted ellipse change. Therefore, from the ratio between the major axis and minor axis of the fitted ellipse, the deflection angle of the observation plane is calculated correspondingly. The deflection angle is the angle θ between the normal vector n of the observation plane and the Z-axis. The calculation formula of θ is as follows:

[0076]

[0077] Since θ can only represent the orientation of the fitted ellipse relative to the camera, therefore, it is also necessary to calculate the orientation of the plane where the fitted ellipse is located in the coordinate system, that is, to determine the angle δ between the plane formed by the normal vector n and the Z-axis and the X-Z plane. The calculation formula of δ is as follows:

[0078]

[0079] Where Φ is the complementary angle of δ, and the calculation formula of Φ is as follows:

[0080] When b = 0 and a < c, Φ = 0;

[0081] When b = 0 and a < c,

[0082] When b ≠ 0 and a < c,

[0083] When b ≠ 0 and a > c,

[0084] Through θ and δ, the orientation of the observation plane where the fitted ellipse is located in the coordinate system can be determined.

[0085] Similarly, select an observation area that intersects with the plane where the above-mentioned fitted ellipse is located, use the above method to perform ellipse fitting on each vertex of this observation area, and obtain the orientation of the plane where this observation area is located in the coordinate system.

[0086] Through the orientations of the two intersecting planes in the coordinate system, the attitude of the calibration module in the coordinate system can be obtained.

[0087] In the above steps, when performing ellipse fitting according to each vertex of the observation area, it depends on the first image information. Under the condition of weak light, the contour of the observation area in the first image information is relatively blurred, resulting in poor accuracy of the fitted ellipse. At this time, the lidar 4 can be used to assist the camera 3 to determine the attitude of the calibration module 1, such as Figure 3As shown in the figure, the lidar 4 is arranged close to the camera 3, and the calibration module 1 is arranged at the center of the circular track 5. The lidar 4 and the camera 3 can move synchronously along the circular track. The specific method for the lidar 4 to determine the attitude of the calibration module 1 is as follows:

[0088] The lidar 4 is used to obtain the echo time and echo intensity of each observation area of the calibration module 1; the attitude of the calibration module 1 is determined according to the echo time and echo intensity.

[0089] Through the echo time, the propagation distance between the lidar 4 and the calibration module 1 can be determined. The echo intensity depends on the propagation distance on the one hand and also on the angle of each observation area relative to the lidar 4, that is, the angle θ between the normal vector n and the Z-axis. When the propagation distance is fixed, the echo intensity has a corresponding relationship with θ. Thus, θ corresponding to multiple observation areas can be obtained according to the echo intensity, and the attitude of the calibration module 1 can be determined from this.

[0090] In step 420, the method for determining the incident angle of the light source includes: step 424, step 425, and step 426.

[0091] Step 424: Based on the first image information, determine the second radiance value and irradiance value corresponding to each observation area on the first image information.

[0092] Step 425: According to the irradiance value, determine the length of the normal vector of the plane where the corresponding observation area is located.

[0093] Step 426: Synthesize the normal vectors corresponding to multiple observation areas to obtain the incident angle of the light source.

[0094] Specifically, as Figure 2 shown, it is common knowledge that when the light is incident on the plane directly, the irradiance value of the plane is the largest. When the angle between the light and the plane decreases, the irradiance value of the plane decreases accordingly. Thus, by measuring the irradiance values of multiple observation areas, the irradiation direction of the light source, that is, the incident angle of the light source, can be determined.

[0095] The plane with the maximum irradiance value can be selected as the reference plane A among multiple observation regions. As common sense, it can be roughly estimated that the light source irradiates the reference plane A in a face-to-face manner. To facilitate the synthesis calculation of vectors, the number of vectors needs to be minimized as much as possible. Therefore, only multiple observation regions around the reference plane A, namely B, C, D, E, and F, are selected. The normal vector corresponding to the observation region A is N1, the normal vector corresponding to the observation region B is N2, the normal vector corresponding to the observation region C is N3, the normal vector corresponding to the observation region D is N4, the normal vector corresponding to the observation region E is N5, and the normal vector corresponding to the observation region F is N6. As described above, there is a definite relative spatial position relationship among multiple observation planes, and the included angle between the normal vectors of any two observation planes is known. The length of the corresponding normal vector can be determined according to the irradiance value of each observation region. The greater the irradiance value, the greater the length of the normal vector. Thus, the included angle and length of each normal vector are determined. In a three-dimensional space, N1, N2, N3, N4, N5, and N6 are synthesized to obtain the vector N, and the direction corresponding to N is the reverse direction of the light source irradiation, thereby being able to determine the incident angle of the light source.

[0096] After obtaining the attitude of the calibration module and the incident angle of the light source, according to the BRDF value corresponding to each observation region, the BRDF characteristics of each observation region in this light source environment can be obtained.

[0097] Step 430: According to the first radiance value of the surface of interest on the object to be measured, match the surface of interest with the observation regions, and determine the BRDF characteristics of the surface of interest in the light source environment.

[0098] Furthermore, step 430 includes:

[0099] The second radiance value corresponding to each observation region is obtained from the first image information. By matching the first radiance value with multiple second radiance values, the second radiance value closest to the first radiance value is found. The observation region corresponding to this second radiance value is the observation region closest to the surface of interest. From the BRDF characteristics of the closest observation region in this light source environment, the BRDF characteristics of the surface of interest in this light source environment can be correspondingly obtained.

[0100] In this embodiment, by setting the calibration module in the shape of a polyhedron, the attitude of the calibration module and the incident angle of the light source can be measured from multiple angles, improving the accuracy of measuring the attitude of the calibration module and the incident angle of the light source. Furthermore, the accuracy of measuring the BRDF characteristics of the surface of the object to be measured is improved, and the accuracy and precision of the measurement are improved while avoiding the field of view blind area.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for using a calibration module, characterized in that, the calibration module includes: a plurality of observation planes, at least two of the plurality of observation planes intersect, and there is a definite relative spatial position relationship between the plurality of observation planes; an observation area is provided on each of the observation planes, and each of the observation areas has a corresponding calibrated BRDF value; the method for using the calibration module includes the following steps: placing the calibration module in the light source environment where the object to be measured is located; obtaining the first image information of the calibration module and the second image information of the object to be measured; based on the first image information, determining the attitude of the calibration module and the incident angle of the light source; based on the second image information, determining the first radiance value of the surface of interest on the object to be measured; according to the first radiance value, matching the surface of interest with the observation area to determine the BRDF characteristics of the surface of interest in the light source environment.

2. The method for using a calibration module according to claim 1, characterized in that, the shape of the observation area includes: equilateral triangle, square, regular pentagon, regular hexagon and regular octagon.

3. The method for using a calibration module according to claim 1, characterized in that, the observation area is divided into a plurality of standard areas, and the plurality of standard areas have at least two BRDF characteristics.

4. The method for using a calibration module according to claim 1, characterized in that, the plurality of observation planes enclose a closed cavity.

5. The method for using a calibration module according to claim 1, characterized in that, the determining the attitude of the calibration module and the incident angle of the light source based on the first image information includes: performing elliptical fitting on the vertices of one of the observation areas on the first image information to obtain a fitted ellipse; obtaining the center coordinates, major axis length and minor axis length of the fitted ellipse; based on the center coordinates, major axis length and minor axis length of the fitted ellipse, determining the orientation of the observation plane corresponding to the fitted ellipse to obtain the attitude of the calibration module.

6. The method for using a calibration module according to claim 1, characterized in that, the determining the attitude of the calibration module and the incident angle of the light source based on the first image information further includes: based on the first image information, determining the second radiance value and irradiance value corresponding to each observation area on the first image information; according to the irradiance value, determining the length of the normal vector of the plane where the corresponding observation area is located; synthesizing the normal vectors corresponding to the plurality of observation areas to obtain the incident angle of the light source.

7. The method for using a calibration module according to claim 6, characterized in that, the matching the surface of interest with the observation area according to the first radiance value to determine the BRDF characteristics of the surface of interest in the light source environment includes: matching the first radiance value with the plurality of second radiance values to determine the observation area corresponding to the surface of interest; Determine the BRDF characteristic of the surface of interest in the light source environment based on the BRDF characteristic of the observation region in the light source environment.

8. The method for using the calibration module according to claim 1, wherein, the determining the attitude of the calibration module and the incident angle of the light source based on the first image information further includes: obtaining the echo time and echo intensity of each observation region of the calibration module; determining the attitude of the calibration module according to the echo time and echo intensity.

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