A planet image pre-screening method based on illumination simulation

Abstract

The present application relates to a kind of planet image pre-screening method based on illumination simulation, comprising: obtaining the target area corresponding to the planet image to be screened, construct rough three-dimensional terrain, obtain the horizon elevation angle of each pixel corresponding to the horizon of each solar azimuth in rough three-dimensional terrain, obtain the horizon map of each solar azimuth;The current solar azimuth of the planet image to be screened is obtained, and the horizon map under the current solar azimuth is calculated;According to the solar disc visible threshold, determine the horizon elevation angle threshold, screen the horizon elevation angle of each pixel, and assign values to whether there is illumination;From rough three-dimensional terrain, obtain the image coverage area covered by the planet image to be screened;The proportion of the pixel with illumination in the image coverage area is calculated, and whether the image is usable is judged.Compared with the prior art, the present application can quickly, accurately and automatically solve the pre-screening problem of planet image, greatly improve the working efficiency of planet three-dimensional mapping and the like.

Description

Technical Field

[0001] This invention relates to the field of planetary three-dimensional mapping technology, and in particular to a method for pre-screening planetary images based on illumination simulation. Background Technology

[0002] In 3D mapping of planetary surfaces, planetary imagery is one of the most important data sources. Planetary imagery preserves a wealth of information, including surface brightness stored in pixel grayscale, as well as satellite orbits, camera attitude, camera parameters, and capture time. Selecting suitable imagery based on the target is the primary task in 3D planetary surface mapping. Currently, planetary image selection mainly relies on the built-in functions of image publishing platforms, listing all potentially covered imagery based on the maximum and minimum latitude and longitude coverage.

[0003] However, this kind of screening has two problems:

[0004] (1) Since the image is long and narrow, when the target area is small, the image that meets the conditions of maximum and minimum latitude and longitude may not exactly cover the target area.

[0005] (2) In areas with complex lighting, the target area may be located under the shadow of high mountains when a large number of images are taken, and there is no usable information in the images.

[0006] Therefore, even after the images are screened by the platform, there may still be a large number of unusable images. These images can usually only be determined by manual judgment or other means after preprocessing such as projection. This is one of the most time-consuming processes in the current work of 3D mapping of planetary surfaces. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the existing technology, which may still contain a large number of unusable images even after conventional platform screening, and to provide a planetary image pre-screening method based on illumination simulation.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] A method for pre-screening planetary images based on illumination simulation includes the following steps:

[0010] Obtain the target area corresponding to the planetary image to be screened. With the target area as the center, construct a rough three-dimensional terrain. Search for the corresponding horizon for each pixel in the rough three-dimensional terrain that falls into the target area and record the horizon elevation angle. Obtain the horizon elevation angle of each pixel corresponding to the horizon at each solar azimuth angle to obtain the horizon map corresponding to each solar azimuth angle.

[0011] Based on the shooting time information in the planetary images to be screened, the corresponding current solar azimuth angle is obtained. Two horizon maps with solar azimuth angles close to the current solar azimuth angle are obtained, and the horizon map under the current solar azimuth angle is calculated. Based on the solar disk visibility threshold, the horizon elevation angle threshold is determined. The horizon elevation angle corresponding to each pixel in the horizon map under the current solar azimuth angle is screened, thereby assigning values ​​for whether the grid corresponding to the rough three-dimensional terrain is illuminated.

[0012] Acquire planetary images to be screened, and obtain the image coverage area covered by the planetary images to be screened from the rough three-dimensional terrain;

[0013] The proportion of illuminated pixels in the image coverage area is calculated and compared with a preset proportion threshold to determine whether the planetary image to be screened is usable, thereby performing the screening.

[0014] Furthermore, the process of searching for the corresponding horizon for each pixel and calculating the horizon elevation angle includes:

[0015] Establish a fixed rectangular coordinate system based on the rough 3D terrain. Starting from the current pixel, obtain the planar coordinates of the sampling points on the rough 3D terrain at preset angular intervals along a specified azimuth angle to obtain the corresponding sampling point height value. Based on the distance between the sampling point and the current pixel, calculate the tangent value of the current pixel's elevation angle. Take the maximum value of the tangent value of the current pixel's elevation angle as the current pixel's horizon elevation angle.

[0016] Furthermore, the resolution accuracy of the rough three-dimensional terrain is above 100 meters.

[0017] Furthermore, based on the shooting time information in the planetary images to be screened, the solar altitude angle, solar azimuth angle, and apparent disk radius corresponding to the shooting time information are obtained by querying the planetary ephemeris.

[0018] Furthermore, the horizon elevation angle threshold is determined based on the visibility threshold of the solar disk. Specifically, the horizon elevation angle threshold is calculated based on the relationship between the visibility threshold of the solar disk and the solar altitude angle, solar azimuth angle, apparent radius of the disk, and the horizon elevation angle of the pixel.

[0019] Furthermore, based on two horizon maps that are close to the current solar azimuth angle, a horizon map under the current solar azimuth angle is obtained by linear interpolation.

[0020] Furthermore, after assigning values ​​to the grids corresponding to the rough 3D terrain to indicate whether they are illuminated or not, a logical value matrix describing whether each grid of the rough 3D terrain is illuminated or not is obtained, which is used for subsequent calculations.

[0021] Furthermore, the logical value matrix is ​​binarized to distinguish whether a grid has light or not.

[0022] Furthermore, the process of acquiring the image coverage area includes:

[0023] Based on the planetary image to be screened, the quadrilateral position covered by the image is obtained. Based on the grid topology of the rough three-dimensional terrain, if the grid center in the grid topology is located inside the quadrilateral position, the corresponding grid center is the covered area; otherwise, it is an uncovered area. All covered areas are taken as the image covered area.

[0024] Furthermore, a parallel computing method is used to calculate whether each pixel in the horizon map is illuminated at the current solar azimuth angle.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] The present invention proposes a planetary image pre-screening method based on illumination simulation. First, the illumination conditions of the target area at the time of shooting are simulated based on the image coverage and shooting time. Then, the image coverage and illumination conditions of the planetary images to be screened are judged. Thus, the usability of the image is determined before the image itself is preprocessed, thereby realizing rapid pre-screening of planetary images.

[0027] This method can quickly, accurately, and automatically solve the problem of pre-screening planetary images, greatly improving the efficiency of planetary 3D mapping. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating a planetary image pre-screening method based on illumination simulation provided in an embodiment of the present invention.

[0029] Figure 2 This is a schematic diagram illustrating a process of searching for the horizon along each azimuth angle for each pixel, as provided in an embodiment of the present invention.

[0030] Figure 3 This is a schematic diagram of a target area provided in an embodiment of the present invention;

[0031] Figure 4 This is a schematic diagram of the image coverage area in a target region provided in an embodiment of the present invention;

[0032] Figure 5 This is a map showing the visible scale of the solar disk at the moment of shooting, provided in an embodiment of the present invention;

[0033] Figure 6 This is a schematic diagram of the illumination situation within a coverage area provided in an embodiment of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0035] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0036] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0037] Example 1

[0038] like Figure 1 As shown, this embodiment provides a planetary image pre-screening method based on illumination simulation, including the following steps:

[0039] S1: Obtain the target area corresponding to the planetary image to be screened. With the target area as the center, construct a rough three-dimensional terrain. Search for the corresponding horizon for each pixel in the rough three-dimensional terrain that falls into the target area and record the horizon elevation angle. Obtain the horizon elevation angle of each pixel corresponding to the horizon at each solar azimuth angle to obtain the horizon map corresponding to each solar azimuth angle.

[0040] Specifically, the process of searching for the corresponding horizon for each pixel and calculating the horizon elevation angle includes:

[0041] Establish a fixed rectangular coordinate system based on the rough 3D terrain. Starting from the current pixel, obtain the planar coordinates of the sampling points on the rough 3D terrain at preset angular intervals along a specified azimuth angle to obtain the corresponding sampling point height value. Based on the distance between the sampling point and the current pixel, calculate the tangent value of the current pixel's elevation angle. Take the maximum value of the tangent value of the current pixel's elevation angle as the current pixel's horizon elevation angle.

[0042] S2: Based on the shooting time information in the planetary images to be screened, obtain the corresponding current solar azimuth angle, obtain two horizon maps with solar azimuth angles close to the current solar azimuth angle, and calculate the horizon map under the current solar azimuth angle; based on the solar disk visibility threshold, determine the horizon elevation angle threshold, and filter the horizon elevation angle corresponding to each pixel in the horizon map under the current solar azimuth angle, thereby assigning values ​​for whether the grid corresponding to the rough 3D terrain is illuminated or not.

[0043] Specifically, based on the shooting time information in the planetary images to be screened, the solar altitude angle, solar azimuth angle, and apparent disk radius corresponding to the shooting time information are obtained by querying the planetary ephemeris.

[0044] The horizon elevation angle threshold is determined based on the visibility threshold of the solar disk. Specifically, the horizon elevation angle threshold is calculated based on the relationship between the visibility threshold of the solar disk and the solar altitude angle, solar azimuth angle, apparent radius of the disk, and the horizon elevation angle of the pixel.

[0045] Based on two horizon maps that are close to the current solar azimuth, a horizon map under the current solar azimuth is obtained by linear interpolation.

[0046] After assigning values ​​to the raster corresponding to the rough 3D terrain to indicate whether it is lit or not, a logical value matrix describing the lighting status of each raster in the rough 3D terrain is obtained, which is used for subsequent calculations.

[0047] S3: Obtain the planetary image to be screened, and obtain the image coverage area covered by the planetary image to be screened from the rough 3D terrain;

[0048] Specifically, the process of acquiring the image coverage area includes:

[0049] Based on the planetary images to be screened, the quadrilateral positions covered by the images are obtained. According to the grid topology of the rough three-dimensional terrain, if the grid center in the grid topology is located inside the quadrilateral position, the corresponding grid center is the covered area; otherwise, it is an uncovered area. All covered areas are taken as the image coverage area.

[0050] S4: Calculate the proportion of illuminated pixels in the image coverage area and compare it with a preset proportion threshold to determine whether the planetary image to be screened is usable, and then perform the screening.

[0051] For example, the above solution specifically includes the following aspects:

[0052] 1. Simulation of illumination conditions in the target area at a specified time:

[0053] 1.1 The creation of the Horizon database;

[0054] First, load a rough 3D terrain map centered on the target area and extending sufficiently to the horizon. Typically, a rough terrain map with a resolution of several hundred meters is sufficient. For each pixel (query point) in the rough terrain that falls within the target area, search for the local horizon at fixed angular intervals and record the elevation angle. This yields a horizon map for each angle (azimuth). Merging all horizon maps creates a horizon database.

[0055] The process of searching the horizon along each azimuth angle for each query point pixel is as follows: Figure 2 As shown, the process includes: first, establishing a fixed rectangular coordinate system based on the terrain; starting from the query point, determining the plane coordinates of the sampling point on the XOY plane at predetermined intervals along a specified azimuth angle; interpolating the sampling point height value on the corresponding terrain surface; and determining the tangent of the elevation angle based on the height value and the distance to the query point, where the maximum value α of the elevation angle is the horizon elevation angle to be recorded.

[0056] 1.2 Pixel-by-pixel illumination calculation at a specific time;

[0057] First, the capture time information is read from the image data to be filtered. Since this information is recorded in the image reference file, which is only a few KB in size, the reading is very fast. By querying the planetary ephemeris, the solar altitude angle, azimuth angle, and apparent radius of the solar disk corresponding to each capture time can be obtained. Then, the two horizon maps closest to the current solar azimuth angle are found in the horizon database, and the horizon map at the current azimuth angle is obtained through linear interpolation. Finally, based on a specified solar disk visibility threshold (e.g., a visible solar disk area greater than 20% is considered illuminated), a horizon elevation angle threshold is determined. Pixels above the corresponding threshold are defined as unilluminated, and those below are defined as illuminated. Illuminated rasters are assigned the value true, and unilluminated rasters are assigned the value false, resulting in a logical value matrix describing the illumination conditions. Illumination calculations can be accelerated using large-scale parallelization techniques.

[0058] 2. Determination of image coverage and lighting conditions

[0059] 2.1 Calculation of image coverage;

[0060] First, the image coverage information is read from the image reference file. Since the image reference file is only a few KB in size, the reading is very fast. Typically, the image coverage information consists of the coordinates of four points; the quadrilateral enclosed by these four points represents the image coverage area. According to the raster topology of the rough terrain, if the raster center is located inside the quadrilateral, it is defined as coverage; otherwise, it is not covered.

[0061] 2.2 Determining whether an image is usable;

[0062] The pixels within the image coverage area are extracted from the illumination condition matrix. The proportion of raster pixels with a value of true is analyzed. If the proportion is greater than a specified threshold (e.g., 20%), the image is considered usable.

[0063] 3. Experiment and Analysis

[0064] This experiment used 77.5-78.5°S and 24.5-27.5°E as the target region, such as... Figure 3 As shown, LRO NAC image information was obtained from the JPL data node. A list of 330 images was obtained using JPL website tools, and the corresponding reference information was downloaded, totaling approximately 2.57MB. Figure 4 The image shown is the image coverage area within the target region; a horizon database was created using coarse terrain at a resolution of 240 meters, and areas where the solar disk is visible exceeding 20% ​​were considered illuminated; as shown... Figure 5 The image shown is a map of the visible proportions of the solar disk at the time of capture. Images with a percentage of illuminated pixels greater than 20% within their coverage area were selected as the filtering criteria, resulting in 153 images. Figure 6 The image shown illustrates the lighting conditions within the coverage area. The experimental platform used an Intel Xeon Gold 6130 CPU, with 32 threads running in parallel computation, taking approximately 15.74 seconds. Taking image "M1302149857RE" as an example, it covers 1410 pixels of the rough terrain of the target area, of which 1122 pixels are illuminated.

[0065] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for pre-screening planetary images based on illumination simulation, characterized in that, Includes the following steps: Obtain the target area corresponding to the planetary image to be screened. With the target area as the center, construct a rough three-dimensional terrain. Search for the corresponding horizon for each pixel in the rough three-dimensional terrain that falls into the target area and record the horizon elevation angle. Obtain the horizon elevation angle of each pixel corresponding to the horizon at each solar azimuth angle to obtain the horizon map corresponding to each solar azimuth angle. Based on the shooting time information in the planetary images to be screened, the corresponding current solar azimuth angle is obtained. Two horizon maps with solar azimuth angles close to the current solar azimuth angle are obtained, and the horizon map under the current solar azimuth angle is calculated. Based on the solar disk visibility threshold, the horizon elevation angle threshold is determined. The horizon elevation angle corresponding to each pixel in the horizon map under the current solar azimuth angle is screened, thereby assigning values ​​for whether the grid corresponding to the rough three-dimensional terrain is illuminated. Acquire planetary images to be screened, and obtain the image coverage area covered by the planetary images to be screened from the rough three-dimensional terrain; The proportion of illuminated pixels in the image coverage area is calculated and compared with a preset proportion threshold to determine whether the planetary image to be screened is usable, thereby performing the screening.

2. The method for pre-screening planetary images based on illumination simulation according to claim 1, characterized in that, The process of searching for the corresponding horizon for each pixel and calculating the horizon elevation angle includes: Establish a fixed rectangular coordinate system based on the rough 3D terrain. Starting from the current pixel, obtain the planar coordinates of the sampling points on the rough 3D terrain at preset angular intervals along a specified azimuth angle to obtain the corresponding sampling point height value. Based on the distance between the sampling point and the current pixel, calculate the tangent value of the current pixel's elevation angle. Take the maximum value of the tangent value of the current pixel's elevation angle as the current pixel's horizon elevation angle.

3. The method for pre-screening planetary images based on illumination simulation according to claim 1, characterized in that, The resolution of the rough three-dimensional terrain is above 100 meters.

4. The method for pre-screening planetary images based on illumination simulation according to claim 1, characterized in that, Based on the shooting time information in the planetary images to be screened, the solar altitude angle, solar azimuth angle, and apparent disk radius corresponding to the shooting time information are obtained by querying the planetary ephemeris.

5. The method for pre-screening planetary images based on illumination simulation according to claim 4, characterized in that, The horizon elevation angle threshold is determined based on the visibility threshold of the solar disk. Specifically, the horizon elevation angle threshold is calculated based on the relationship between the visibility threshold of the solar disk and the solar altitude angle, solar azimuth angle, apparent radius of the disk, and the horizon elevation angle of the pixel.

6. The method for pre-screening planetary images based on illumination simulation according to claim 1, characterized in that, Based on two horizon maps that are close to the current solar azimuth, a horizon map under the current solar azimuth is obtained by linear interpolation.

7. The method for pre-screening planetary images based on illumination simulation according to claim 1, characterized in that, After assigning values ​​to the grids corresponding to the rough 3D terrain to indicate whether they are illuminated or not, a logical value matrix describing the illumination status of each grid in the rough 3D terrain is obtained, which is used for subsequent calculations.

8. The method for pre-screening planetary images based on illumination simulation according to claim 7, characterized in that, The logical value matrix is ​​assigned a binary value to distinguish whether a grid has light or not.

9. The method for pre-screening planetary images based on illumination simulation according to claim 1, characterized in that, The process of acquiring the image coverage area includes: Based on the planetary image to be screened, the quadrilateral position covered by the image is obtained. Based on the grid topology of the rough three-dimensional terrain, if the grid center in the grid topology is located inside the quadrilateral position, the corresponding grid center is the covered area; otherwise, it is an uncovered area. All covered areas are taken as the image covered area.

10. The method for pre-screening planetary images based on illumination simulation according to claim 1, characterized in that, Parallel computing methods are used to calculate whether each pixel in the horizon map is illuminated at the current solar azimuth angle.

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