Spherical spiral continuous scanning method and luminous intensity distribution reconstruction method

Abstract

The invention discloses a spherical spiral continuous scanning method and a luminous intensity distribution reconstruction method.The spherical spiral continuous scanning method comprises the steps that an azimuth axis and a pitch axis of a near-field distribution photometer synchronously and continuously rotate at a certain rotating speed ratio n, and the pitch axis continuously rotates from 0 degree to a certain angle larger than 0 degree and smaller than or equal to 180 degrees; meanwhile, the azimuth axis continuously rotates from 0 degree until the pitch axis stops rotating; an imaging brightness meter in the near-field distribution photometer forms a spherical spiral line relative to a scanning track of the measured light source; the luminous intensity distribution reconstruction method comprises the following steps: dividing a scanning spherical surface into surface elements with similar areas by using a Delaunay triangulation algorithm, calculating light data in each sampling direction, and comprehensively obtaining full-space luminous intensity distribution. According to the spherical spiral continuous scanning method and the luminous intensity distribution reconstruction method provided by the invention, the sampling data volume can be reduced, the near-field distribution luminosity measurement speed can be improved, and higher measurement precision can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of near-field distributed photometry, and in particular to a spherical spiral continuous scanning method and a luminous intensity distribution reconstruction method. Background Art

[0002] Near-field distributed photometry is an important method for obtaining the luminous characteristics of light sources and screen display performance. It collects brightness data in all directions and calculates the set of light radiation fluxes at any point on the light source based on the spatial position relationship. It can break through the limitations of physical space on light radiation measurement and achieve full-space light field measurement of light sources. Near-field distributed photometry has important applications in lighting engineering, virtual reality, light source evaluation and other fields. It can assist in the design and optimization of lighting systems, evaluate the performance and quality of light sources, and provide relevant data and indicators for lighting. It plays a vital role in the design, evaluation and research of optical systems, supporting the high-quality design of light sources and screens and the development of precision optical systems. Therefore, near-field distributed photometry has gradually become a research hotspot in optical measurement technology.

[0003] However, existing near-field distributed photometry research mostly uses a spherical grid step scanning method, that is, the azimuth axis and the pitch axis are incrementally scanned with a fixed step size. The acquired brightness data is unevenly distributed in space, and the sampling directions are repeated in the polar regions of the scanning sphere, resulting in data redundancy, affecting the brightness data acquisition speed and light field reconstruction speed. In addition, the sampling directions near the equator of the scanning sphere are often insufficient, which limits the accuracy of light field reconstruction. Summary of the invention

[0004] Purpose of the invention: To address the problems of insufficient measurement speed and accuracy of the spherical grid step scanning commonly used in near-field distributed photometry, the present invention proposes a spherical spiral continuous scanning method and a luminous intensity distribution reconstruction method.

[0005] Technical solution: The spherical spiral continuous scanning method described in the present invention is implemented as follows:

[0006] The azimuth axis and the elevation axis of the near-field goniophotometer rotate synchronously and continuously at a certain speed ratio n. The elevation axis rotates continuously from 0° to an angle greater than 0° and less than or equal to 180°, and the azimuth axis rotates continuously from 0° until the elevation axis stops rotating. The imaging luminance meter in the near-field goniophotometer forms a spherical spiral relative to the scanning trajectory of the light source being measured.

[0007] Furthermore, the near-field distribution photometer includes two motors, which respectively drive the azimuth axis and the pitch axis to rotate; a conductive slip ring is used at the connection between the measured light source and the motor to ensure that the rotation angle of the azimuth axis can be greater than 360° and continue to increase without causing cable entanglement.

[0008] Furthermore, the sampling of the imaging luminance meter is triggered by the programmable logic controller hardware in the near-field distribution photometer.

[0009] Furthermore, the azimuth angle and the elevation angle of the initial sampling direction of the imaging luminance meter are both 0°, and the intersection points of two adjacent sampling directions with the scanning sphere are distributed at equal intervals on the spherical spiral line.

[0010] Furthermore, the equal spacing s=2πr / n, wherein r is the radius of the scanning sphere.

[0011] Furthermore, the speed ratio n=360° / Δθ, wherein Δθ is the expected angle sampling accuracy.

[0012] The luminous intensity distribution reconstruction method suitable for spherical spiral continuous scanning described in the present invention is implemented as follows:

[0013] S1: Calculate the coordinates of the intersections between all sampling directions of the imaging luminance meter and the scanning sphere;

[0014] S2: using the Delaunay triangulation algorithm, taking the intersection points obtained in step S1 as vertices, the scanned sphere is divided into approximately uniform triangular units;

[0015] S3: Take the centroid of the triangular unit and project all centroids onto the scanning sphere along the radial direction to obtain a series of projected centroids;

[0016] S4: Connect the projection centroids of the triangular units that share the same vertex along the great circle to form a spherical polygon;

[0017] S5: Calculate the area ΔA of each spherical polygon;

[0018] S6: Calculate the luminous flux of each pixel corresponding to the light in all brightness images obtained by continuous spiral scanning of the spherical surface;

[0019] S7: Solid Angle The contribution of all rays in the image is added together to obtain the value at the pitch angle θ k , azimuth Luminous intensity in direction

[0020] S8: Traverse the pitch angle θ in step S7 k and azimuth Get the luminous intensity distribution of the measured light source.

[0021] Furthermore, the area ΔA of the spherical polygon is calculated as follows:

[0022] Compute the area of ​​the triangle formed by the projected centroid and vertices:

[0023]

[0024] Wherein, m is the serial number of the triangle contained in the spherical polygon, s is half of the perimeter of the triangle, and a, b and c are the lengths of the three sides of the triangle respectively;

[0025] The area of ​​a spherical polygon is approximately equal to the sum of the areas of all the triangles it contains:

[0026]

[0027] Furthermore, the luminous flux of the light corresponding to each pixel is:

[0028]

[0029] Among them, (x w ,y w ,z w ) is the coordinate of the pixel in the world coordinate system, θ w and are the pitch angle and azimuth of the light in the world coordinate system, L is the brightness of the light, θ c is the angle between the light and the z-axis of the camera coordinate system, and ΔΩ is the solid angle of the pixel to the center of the lens exit pupil.

[0030] Furthermore, the luminous intensity for:

[0031]

[0032] Among them, (x w ,y w ,z w ) is the coordinate of the pixel in the world coordinate system, θ w and are the pitch angle and azimuth angle of the light in the world coordinate system respectively.

[0033] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects: the spherical spiral continuous scanning method for near-field distributed photometry proposed in the present invention makes the spatial distribution of the sampling direction of the imaging luminance meter more uniform, and when used in conjunction with the proposed luminous intensity distribution reconstruction method, it can achieve higher-precision light field reconstruction while reducing the sampling directions; the reduction in sampling directions can increase the measurement speed; in addition, both the azimuth axis and the pitch axis rotate continuously in one direction, avoiding frequent acceleration and deceleration caused by the reciprocating motion of the pitch axis in the spherical grid step scanning, thereby further increasing the measurement speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic diagram of a spherical spiral scanning trajectory of an imaging luminance meter relative to a light source to be measured in an embodiment of the present invention;

[0035] Figure 2 Schematic diagram of the structure of a near-field distribution photometer in an embodiment of the present invention;

[0036] Figure 3 is the azimuth of the sampling direction in the embodiment of the present invention Schematic diagram of the definition of the pitch angle θ;

[0037] Figure 4 Schematic diagram of spatial distribution of intersection points between the sampling direction of spherical spiral continuous scanning and the scanning sphere in an embodiment of the present invention;

[0038] Figure 5 Schematic diagram of spatial distribution of intersections between the sampling direction of the spherical grid step scanning and the scanning sphere in an embodiment of the present invention;

[0039] Figure 6 Schematic diagram of spherical triangulation result of spherical spiral continuous scanning in an embodiment of the present invention;

[0040] Figure 7 Schematic diagram of the distribution of projection gravity centers of the scanning spherical triangular unit in an embodiment of the present invention;

[0041] Figure 8 A schematic diagram of a spherical polygon formed by connecting the projection centroids of triangular units in an embodiment of the present invention;

[0042] Fig. 9 A schematic diagram of a spherical polygon triangulation result in an embodiment of the present invention;

[0043] Fig.10 A schematic diagram of a camera coordinate system established on an imaging luminance meter in an embodiment of the present invention;

[0044] Fig.11 Schematic diagram of luminous intensity distribution reconstructed by different measurement methods in an embodiment of the present invention. DETAILED DESCRIPTION

[0045] The present invention is further described in detail below with reference to the accompanying drawings.

[0046] The present invention proposes a spherical spiral continuous scanning method, and the specific implementation method is as follows: the azimuth axis and the pitch axis of a near-field distribution photometer rotate synchronously and continuously at a certain rotation speed ratio n, the pitch axis rotates continuously from 0° to an angle greater than 0° and less than or equal to 180°, and at the same time, the azimuth axis rotates continuously from 0° until the pitch axis stops rotating; the imaging luminance meter in the near-field distribution photometer forms a spherical spiral line relative to the scanning trajectory of the light source to be measured.

[0047] In this embodiment, the azimuth axis and the elevation axis of the near-field distribution photometer rotate synchronously and continuously at a speed ratio of n=72. The elevation axis rotates continuously from 0° to 150°, and the azimuth axis rotates continuously from 0° to 10800°. The scanning trajectory of the imaging luminance meter relative to the measured light source forms a spherical spiral line, as shown in FIG. Figure 1 shown.

[0048] Spatial scanning can be achieved by one of three motion modes: 1. The measured light source is fixed, and the imaging brightness meter performs spatial scanning under the drive mechanism of the azimuth axis and the pitch axis; 2. The imaging brightness meter is fixed, and the measured light source is driven by the drive mechanism of the azimuth axis and the pitch axis to perform spatial scanning; 3. The measuring light source rotates under the drive mechanism of the azimuth axis, and the imaging brightness meter rotates under the drive mechanism of the pitch axis to perform spatial scanning. Among them, the specific implementation of the second motion mode is as follows:

[0049] Customized near-field goniophotometers such as Figure 2 As shown, it includes two motors, which drive the azimuth axis 1 and the pitch axis 2 to rotate respectively, and drive the measured light source 3 to rotate around the luminous center. A conductive slip ring is used at the connection between the measured light source 3 and the motor to ensure that the rotation angle of the azimuth axis 1 can be greater than 360° and continue to increase without causing cable entanglement. The measured light source 3 adopts a square lamp with a luminous size of 100mm×100mm×15mm and a power of 20W. Its far-field luminous intensity distribution has been measured in advance. The imaging luminance meter 4 is composed of an industrial camera with a resolution of 1920×1200 and a lens, which is fixed by a bracket 5. The sampling of the imaging luminance meter 4 is triggered by the programmable logic controller (PLC) hardware in the motion control box 6. The distance between the measured light source 3 and the imaging luminance meter 4 is about 0.5m.

[0050] The azimuth of the starting sampling direction of the imaging brightness meter and the pitch angle θ are both 0°. Figure 3 As shown, the azimuth It is defined as the angle between the projection of the sampling direction on the xy plane and the positive direction of the x-axis; the pitch angle θ is defined as the angle between the sampling direction and the positive direction of the z-axis. The spacing between the intersection points of two adjacent sampling directions of the imaging luminance meter and the scanning sphere on the spherical spiral line is s = 2πr / n≈43.6mm, where r is the radius of the scanning sphere, which is approximately equal to the distance between the measured light source and the imaging luminance meter. Whenever the imaging luminance meter reaches the specified sampling direction, the programmable logic controller triggers the imaging luminance meter to sample the brightness data in the current direction. The spatial distribution of the intersection points of all sampling directions of the imaging luminance meter and the scanning sphere is shown in the figure. Figure 4 As shown, there are 1712 intersection points in total.

[0051] The relationship between the rotation speed ratio n and the expected angle sampling accuracy Δθ is n=360° / Δθ. It can be calculated that the expected angle sampling accuracy of the above spherical spiral continuous scanning method is 5°.

[0052] For comparison, the total number of sampling directions of the spherical grid step scanning method with the same angular sampling accuracy and spatial sampling range is 2196, and its azimuth axis rotates from 0° to 175° in 5° steps, and its elevation axis rotates from –150° to 150° in 5° steps; the spatial distribution of the intersection points of all sampling directions and the scanning sphere is shown in Figure 5 As shown, there are 2196 intersection points. Figure 4 and Figure 5 It can be found that the spatial distribution of the intersection points obtained by the spherical spiral continuous scanning is relatively uniform, while the spatial distribution of the intersection points obtained by the spherical grid step scanning is uneven, which is denser near the poles of the scanning sphere and sparser near the equator.

[0053] The present invention also proposes a method for reconstructing the luminous intensity distribution suitable for spherical spiral continuous scanning. The specific implementation method is as follows: calculate the intersection coordinates of all sampling directions of the imaging luminance meter and the scanning sphere, and obtain Figure 4 In order to make the areas of the corresponding facets in different sampling directions as equal as possible, the Delaunay triangulation algorithm is used to Figure 4 The intersection points in are taken as vertices, and the scanned sphere is divided into approximately uniform triangular units, such as Figure 6 As shown in the figure. Since the triangular units are not centered at the intersection of the sampling direction and the scanning sphere, they cannot be regarded as surface elements to calculate the luminous flux. Figure 6 The centroids of all triangular units shown in the figure are projected radially onto the scanning sphere to obtain a series of projected centroids, such as Figure 7 The projection centroids of the triangular units that share the same vertex are connected along the great circle to form a spherical polygon, which is regarded as the surface element corresponding to the sampling direction, as shown in Figure 8 As shown, for simplicity, only one spherical polygon is drawn in the figure.

[0054] Calculate the area ΔA of each spherical polygon using approximate calculations: Fig. 9 As shown, the spherical polygon is divided into several triangles consisting of the projection centroid and vertices. There are 6 triangles in the figure, and the area of ​​each triangle is recorded as ΔA1, ΔA2, ΔA3, ΔA4, ΔA5, and ΔA6 respectively; calculate the area of ​​each triangle Where m = 1 to 6, s is half of the perimeter of the triangle, and a, b, and c are the lengths of the three sides of the triangle respectively; the area of ​​a spherical polygon is approximately equal to the sum of the areas of all the triangles it contains:

[0055] Before calculating the luminous flux of each pixel in the brightness image sampled by the imaging brightness meter, two coordinate systems need to be established: one is the world coordinate system, with the luminous center of the measured light source as the origin, the z-axis perpendicular to the surface of the measured light source, and the x-axis and y-axis parallel to the two sides of the measured light source; the other is the camera coordinate system, with the exit pupil center of the imaging brightness meter as the origin, the z-axis perpendicular to the image sensor, and the x-axis and y-axis parallel to the width and height directions of the image sensor, respectively, as shown in Figure 1. Fig.10 shown.

[0056] In the camera coordinate system, the coordinates of the image sensor pixels are:

[0057]

[0058] Wherein, the subscript c denotes the parameter in the camera coordinate system, i and j denote the number of pixels from the center pixel of the image sensor along the positive x-axis and y-axis, respectively, W and H are the width and height of a single pixel on the image sensor, respectively, and f is the focal length of the imaging photometer lens, assuming that the lens is an ideal thin lens.

[0059] The corresponding coordinates of the pixel in the world coordinate system can be calculated:

[0060]

[0061] The subscript w represents the parameter in the world coordinate system, (x p,w ,y p,w ,z p,w ) is the coordinate of the lens exit pupil in the world coordinate system, and the subscript p represents the exit pupil. Then the direction vector of the light corresponding to each pixel on the image sensor can be determined:

[0062]

[0063] The brightness of light can be expressed as L(x w ,y w ,z w ,n x ,n y ,n z ), the propagation direction of the light can be recorded as Its relationship with the direction vector is:

[0064]

[0065] Among them, θ w and They respectively represent the pitch angle and azimuth angle of the light propagation direction in the world coordinate system.

[0066] At this time, the brightness of the light can be recorded as Calculate the luminous flux it carries:

[0067]

[0068] Among them, θ c is the angle between the light and the z-axis of the camera coordinate system, and ΔΩ is the solid angle of the pixel to the center of the lens exit pupil.

[0069] The solid angle Adding up the contributions of all rays in the image gives k , azimuth (k and l are integers) Luminous intensity in the direction:

[0070]

[0071] Traversing the pitch angle θ k and azimuth The luminous intensity distribution of the measured light source can be obtained.

[0072] The luminous intensity distribution of the measured light source is reconstructed using the brightness data of 1712 sampling directions obtained by spherical spiral continuous scanning and the brightness data of 2196 sampling directions obtained by spherical grid step scanning, and these near-field reconstruction results are compared with the far-field reconstruction results, as shown in Figure 2. Fig.11 Azimuth shown The luminous intensity distribution at .

[0073] In order to evaluate the measurement accuracy of different scanning and reconstruction methods, a matching index with far-field luminous intensity distribution as a reference is introduced:

[0074]

[0075] in, represents the far-field test results, Indicates the near field test result. The larger the matching index, the higher the measurement accuracy.

[0076] The matching indexes of the spherical spiral continuous scanning reconstruction results and the spherical grid step scanning reconstruction results are shown in Table 1.

[0077] Table 1 Matching index of different scanning and reconstruction methods

[0078]

[0079] It can be seen that when the number of sampling directions is reduced by 22%, the matching index of the spherical spiral continuous scanning reconstruction result is higher than that of the spherical grid step scanning reconstruction result.

[0080] The above descriptions are merely embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in other related technical fields, should be included in the protection scope of the present invention.

Claims

1. A spherical spiral continuous scanning method, characterized in that: The implementation process of the method is as follows: The azimuth axis and the elevation axis of the near-field goniophotometer rotate synchronously and continuously at a certain speed ratio n. The elevation axis rotates continuously from 0° to an angle greater than 0° and less than or equal to 180°, and the azimuth axis rotates continuously from 0° until the elevation axis stops rotating. The imaging luminance meter in the near-field goniophotometer forms a spherical spiral relative to the scanning trajectory of the light source being measured.

2. A spherical spiral continuous scanning method according to claim 1, characterized in that: The near-field distribution photometer comprises two motors, which respectively drive the azimuth axis and the elevation axis to rotate; a conductive slip ring is used at the connection between the measured light source and the motor to ensure that the rotation angle of the azimuth axis can be greater than 360° and can be continuously increased without causing cable entanglement.

3. A spherical spiral continuous scanning method according to claim 1, characterized in that: The sampling of the imaging luminance meter is triggered by the programmable logic controller hardware in the near-field distribution photometer.

4. A spherical spiral continuous scanning method according to claim 1, characterized in that: The azimuth angle and the pitch angle of the initial sampling direction of the imaging luminance meter are both 0°, and the intersection points of two adjacent sampling directions with the scanning sphere are distributed at equal intervals on the spherical spiral line.

5. A spherical spiral continuous scanning method according to claim 4, characterized in that: The equal spacing s=2πr / n, wherein r is the radius of the scanning sphere.

6. A spherical spiral continuous scanning method according to claim 1, characterized in that: The speed ratio in is the expected angle sampling accuracy.

7. A method for reconstructing luminous intensity distribution applicable to the spherical spiral continuous scanning method according to any one of claims 1 to 6, characterized in that: The implementation process is as follows: S1: Calculate the coordinates of the intersections between all sampling directions of the imaging luminance meter and the scanning sphere; S2: using the Delaunay triangulation algorithm, taking the intersection points obtained in step S1 as vertices, the scanned sphere is divided into approximately uniform triangular units; S3: Take the centroid of the triangular unit and project all centroids onto the scanning sphere along the radial direction to obtain a series of projected centroids; S4: Connect the projection centroids of the triangular units that share the same vertex along the great circle to form a spherical polygon; S5: Calculate the area ΔA of each spherical polygon; S6: Calculate the luminous flux of each pixel corresponding to the light in all brightness images obtained by continuous spiral scanning of the spherical surface; S7: Solid Angle The contribution of all rays within is added together to obtain the pitch angle Azimuth Luminous intensity in direction S8: Traverse the pitch angles in step S7 and azimuth Get the luminous intensity distribution of the measured light source.

8. The method for reconstructing luminous intensity distribution suitable for spherical spiral continuous scanning according to claim 7, characterized in that: The calculation process of the area ΔA of the spherical polygon is as follows: Compute the area of ​​the triangle formed by the projected centroid and vertices: Wherein, m is the serial number of the triangle contained in the spherical polygon, s is half of the perimeter of the triangle, and a, b and c are the lengths of the three sides of the triangle respectively; The area of ​​a spherical polygon is approximately equal to the sum of the areas of all the triangles it contains:

9. The method for reconstructing luminous intensity distribution suitable for spherical spiral continuous scanning according to claim 7, characterized in that: The luminous flux of the light corresponding to each pixel is: Among them, (x w ,y w ,z w ) is the coordinate of the pixel in the world coordinate system, and are the pitch angle and azimuth of the light in the world coordinate system, L is the brightness of the light, is the angle between the light and the z-axis of the camera coordinate system, and ΔΩ is the solid angle of the pixel to the center of the lens exit pupil.

10. The method for reconstructing luminous intensity distribution suitable for spherical spiral continuous scanning according to claim 7, characterized in that: The luminous intensity for: Among them, (x w ,y w ,z w ) is the coordinate of the pixel in the world coordinate system, and are the pitch angle and azimuth angle of the light in the world coordinate system respectively.

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