Shadow rendering method and device based on Monte Carlo method

Abstract

The present invention relates to the field of graphics rendering technology, and discloses a shadow rendering method and device based on the Monte Carlo method, which aims to solve the problem that the existing satellite image display effect is poor and is not conducive to the user's rapid identification of terrain. The scheme mainly includes: obtaining a map tile to be rendered and a satellite rendering image corresponding to it; obtaining all adjacent map tiles of the map tile to be rendered, and splicing the map tile to be rendered and its adjacent map tiles to obtain a texture map; obtaining a digital elevation model corresponding to the map tile to be rendered and its adjacent map tiles; obtaining a height map texture buffer object according to the digital elevation model, and calculating a corresponding normal map texture buffer object; setting a simulated light source, and generating a lighting texture rendering image corresponding to the map tile to be rendered based on the Monte Carlo method; merging the satellite rendering image and the lighting texture rendering image to obtain a final rendering image of the map tile to be rendered. The present invention improves the display effect of satellite images.

Description

Technical Field

[0001] The present invention relates to the field of graphics rendering technology, and in particular to a Monte Carlo-based shadow rendering method and device. Background Art

[0002] In the existing satellite image presentation scheme, satellite images are usually obtained by processing remote sensing data collected by ground-orbiting satellites. Since the satellite sensors are far away from the ground and the image is vast, the sunlight in the natural environment cannot produce large-scale obvious shadows on the surface morphology under the effect of atmospheric scattering. This means that although humans can see "shadows" when living on the surface, the surface reflection signals actually collected by satellite sensors do not have the ideal "artifact form" at the visual level. At the same time, as standardized remote sensing results, the product satellite images produced by remote sensing satellites usually implement atmospheric correction, which is used to shield the systematic errors in the observation results under different meteorological conditions. This further causes the remote sensing satellite image results to present a "flat" visual effect. Users cannot intuitively feel the mountains and canyons from the picture. Not only is the display effect poor, but it is also not conducive to users' rapid identification of terrain. Summary of the invention

[0003] The present invention aims to solve the problem that the existing satellite images have poor display effects and are not conducive to users' rapid identification of terrain, and proposes a shadow rendering method and device based on the Monte Carlo method.

[0004] The technical solution adopted by the present invention to solve the above technical problems is:

[0005] In one aspect, a shadow rendering method based on the Monte Carlo method is provided, comprising the following steps:

[0006] Get the map tile to be rendered and its corresponding satellite rendering;

[0007] Acquire all adjacent map tiles of the map tile to be rendered according to the position information of the map tile to be rendered, and obtain a texture map after splicing the map tile to be rendered and its adjacent map tiles;

[0008] Obtaining a digital elevation model corresponding to the map tile to be rendered and its adjacent map tiles, wherein the digital elevation model is used to represent the undulating form of ground elevation;

[0009] Rendering the texture map to an off-screen buffer of a graphics processor, obtaining a height map texture buffer object corresponding to the texture map according to the digital elevation model, and calculating a corresponding normal map texture buffer object according to the height map texture buffer object;

[0010] Setting a simulated light source, generating a lighting texture rendering image corresponding to the map tile to be rendered according to the height map texture buffer object and the normal map texture buffer object and based on the Monte Carlo method, wherein the lighting texture rendering image is used to represent the lighting range and shadow distribution of the map tile to be rendered under the simulated light source;

[0011] The satellite rendering image and the light texture rendering image are combined to obtain a final rendering image of the map tile to be rendered.

[0012] Further, generating a lighting texture rendering image corresponding to the map tile to be rendered based on the height map texture buffer object and the normal map texture buffer object and based on the Monte Carlo method, specifically includes:

[0013] Iterate according to a preset number of times, each iteration comprising the following steps: randomly determine a point light source in the simulated light source, construct a light from the point light source to the map tile to be rendered along the direction from the point light source to the pixel point corresponding to the map tile to be rendered, and perform fragment coloring on each pixel point under the action of the light according to the height map texture buffer object and the normal map texture buffer object;

[0014] The results of each iteration are mixed to obtain the lighting texture rendering corresponding to the map tile to be rendered.

[0015] Furthermore, the radius of the simulated light source is greater than the radius of the sun.

[0016] Furthermore, the radius of the simulated light source is 67541100 kilometers.

[0017] Furthermore, the preset number of times is 128 times.

[0018] Furthermore, the obtaining of the map tile to be rendered and its corresponding satellite rendering specifically includes:

[0019] Acquire the full amount of data, and slice the satellite images corresponding to the full amount of data to obtain map tiles and their corresponding satellite renderings;

[0020] Get the map tile to be rendered and its corresponding satellite rendering according to the location information.

[0021] Furthermore, the satellite image is sliced ​​based on the Mercator projection to obtain map tiles and their corresponding satellite renderings.

[0022] Furthermore, the digital elevation model is packaged using MapTiler standard.

[0023] On the other hand, a shadow rendering device based on the Monte Carlo method is provided, comprising:

[0024] An acquisition unit is used to acquire a map tile to be rendered and its corresponding satellite rendering image; and to acquire a digital elevation model corresponding to the map tile to be rendered and its adjacent map tiles, wherein the digital elevation model is used to represent the undulating form of the ground elevation;

[0025] A splicing unit, used for acquiring all adjacent map tiles of the map tile to be rendered according to the position information of the map tile to be rendered, and splicing the map tile to be rendered and its adjacent map tiles to obtain a texture map;

[0026] A graphics processing unit, configured to render the texture map into an off-screen buffer of a graphics processor, obtain a height map texture buffer object corresponding to the texture map according to the digital elevation model, and calculate a corresponding normal map texture buffer object according to the height map texture buffer object;

[0027] A rendering unit, used to set a simulated light source, and generate a lighting texture rendering image corresponding to the map tile to be rendered based on the height map texture buffer object and the normal map texture buffer object and based on the Monte Carlo method, wherein the lighting texture rendering image is used to represent the lighting range and shadow distribution of the map tile to be rendered under the simulated light source;

[0028] The merging unit is used to merge the satellite rendering image and the light texture rendering image to obtain a final rendering image of the map tile to be rendered.

[0029] Furthermore, the rendering unit is specifically used for:

[0030] Iterate according to a preset number of times, each iteration comprising the following steps: randomly determine a point light source in the simulated light source, construct a light from the point light source to the map tile to be rendered along the direction from the point light source to the pixel point corresponding to the map tile to be rendered, and perform fragment coloring on each pixel point under the action of the light according to the height map texture buffer object and the normal map texture buffer object;

[0031] The results of each iteration are mixed to obtain the lighting texture rendering corresponding to the map tile to be rendered.

[0032] The beneficial effect of the present invention is that the shadow rendering method and device based on the Monte Carlo method described in the present invention simulate the sun by setting a simulated light source, and generate a lighting texture rendering image of the map tile to be rendered under the simulated light source based on the Monte Carlo method, and finally merge the satellite rendering image and the lighting texture rendering image of the tile to be rendered to complete the shadow rendering of the map tile to be rendered, thereby improving the display effect of the satellite image, and the user can also quickly identify the terrain, such as hilly areas, based on the image after shadow rendering. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1A schematic diagram of a shadow rendering method based on the Monte Carlo method according to an embodiment of the present invention;

[0034] Figure 2 A satellite rendering image under the standard ZXY slicing scheme described in an embodiment of the present invention;

[0035] Figure 3 A digital elevation model under the standard ZXY slicing scheme described in an embodiment of the present invention;

[0036] Figure 4 A schematic diagram of a shadow area according to an embodiment of the present invention;

[0037] Figure 5 A schematic diagram of performing one iteration of randomly selecting a point light source according to an embodiment of the present invention;

[0038] Figure 6 A schematic diagram of performing another iteration on randomly selected point light sources according to an embodiment of the present invention;

[0039] Figure 7 The lighting texture rendering image described in the embodiment of the present invention;

[0040] Figure 8 The final rendering according to the embodiment of the present invention;

[0041] Fig. 9 It is a schematic diagram of the structure of a shadow rendering device based on the Monte Carlo method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0043] The shadow rendering method and device based on the Monte Carlo method provided by the present invention have the following main technical concepts: obtaining a map tile to be rendered and its corresponding satellite rendering image; obtaining all adjacent map tiles of the map tile to be rendered according to the position information of the map tile to be rendered, and obtaining a texture image after splicing the map tile to be rendered and its adjacent map tiles; obtaining a digital elevation model corresponding to the map tile to be rendered and its adjacent map tiles, wherein the digital elevation model is used to represent the undulating form of the ground elevation; rendering the texture image into an off-screen buffer of a graphics processor, obtaining a height map texture buffer object corresponding to the texture image according to the digital elevation model, and calculating a corresponding normal map texture buffer object according to the height map texture buffer object; setting a simulated light source, and generating a lighting texture rendering image corresponding to the map tile to be rendered according to the height map texture buffer object and the normal map texture buffer object and based on the Monte Carlo method, wherein the lighting texture rendering image is used to represent the lighting range and shadow distribution of the map tile to be rendered under the simulated light source; and merging the satellite rendering image and the lighting texture rendering image to obtain a final rendering image of the map tile to be rendered.

[0044] The Monte Carlo method (also known as the statistical test method) is a basic method for describing various random phenomena in the process of equipment operation, and it is particularly suitable for some problems that are difficult or even impossible to solve by analytical methods, so it plays an important role in equipment effectiveness evaluation. The basic idea of ​​the Monte Carlo method is: in order to solve the problem, first establish a probability model or random process so that its parameters or numerical characteristics are equal to the solution of the problem: then calculate these parameters or numerical characteristics through observation or sampling tests of the model or process, and finally give the approximate value of the solution. The accuracy of the solution is expressed by the standard error of the estimate. The main theoretical basis of the Monte Carlo method is the probability and statistical theory, and the main means are random sampling and statistical experiments.

[0045] It is common sense that, without the interference of atmospheric scattering, a surface light source illuminating a three-dimensional surface will produce two different types of shadow areas, the umbra area is completely dark, and the penumbra area is partially illuminated. The closer to the umbra area, the weaker the light. And because the ground set shape is an unpredictable discrete function, if you want to accurately calculate the illumination intensity of the penumbra area mathematically, you need to introduce a highly complex partial integral, and the difficulty set of solving this integral cannot be directly completed by a computer. Based on this, the present invention performs shadow rendering on the satellite rendering corresponding to the rendered map tile based on the Monte Carlo method, that is, the test area is iterated multiple times in a probabilistic way, simulating the ray tracing from different random areas inside the surface light source (imaginary sun), and generating a shadow grayscale image for representing the equivalent illumination range and shadow distribution projected by the imaginary surface light source on the ground in each iteration. After the test is completed, the iterative results are mixed to generate a smooth-edged illumination texture rendering image, which can be used to count the equivalent illumination range and shadow distribution projected by the simulated light source on the ground. Finally, by merging the satellite rendering image and the illumination texture rendering image, the shadow rendering of the penumbra area of ​​the satellite rendering image can be completed.

[0046] Example

[0047] The shadow rendering method based on the Monte Carlo method described in the embodiment of the present invention is as follows: Figure 1 As shown, the following steps are included:

[0048] Step 1: Get the map tile to be rendered and its corresponding satellite rendering;

[0049] It is understandable that the data sets in the field of GIS are generally extremely large. Specifically for the data corresponding to satellite images, their theoretical spatial scale covers the entire surface of the earth. However, modern computers usually do not have the performance requirements to process the entire amount of data at one time. Therefore, the entire data set is usually divided into several small-scale independent units through a slicing scheme to form a raster data set. Local calculations are performed in an autonomous manner among adjacent units. The logical requirement for the sub-domain division is only that the effective data of the sub-domain covers the full input of the local calculation of the sub-domain.

[0050] There are many slicing schemes for raster datasets. This embodiment uses the standard ZXY slicing scheme of the Mercator projection promoted by Google to slice satellite images. Figure 2 and Figure 3 As shown, after executing the standard ZXY slicing scheme, a satellite rendering and a digital elevation model corresponding to the map tile can be obtained, wherein the digital elevation model is used to represent the undulating shape of the ground elevation. The digital elevation model in this embodiment adopts the MapTiler standard package.

[0051] This embodiment can build a slice publishing service to implement an HTTP service that can obtain any geographic location and slice level data by passing in [z, x, y] parameters, so as to obtain the map tiles to be rendered and their corresponding satellite renderings and digital elevation models based on the location information.

[0052] Step 2: acquiring all adjacent map tiles of the map tile to be rendered according to the position information of the map tile to be rendered, and splicing the map tile to be rendered and its adjacent map tiles to obtain a texture map;

[0053] It is understandable that the shadow of the map tile to be rendered will be affected by the terrain of its adjacent map tiles. Therefore, in the shadow rendering process of the penumbra area of ​​the map tile to be rendered, the terrain of the adjacent map tiles needs to be considered to improve the accuracy of the shadow rendering. This embodiment performs eight-domain expansion based on the map tile to be rendered, that is, the map tile to be rendered and its eight adjacent map tiles are spliced, and the shadow of the map tile to be rendered is rendered according to the spliced ​​texture map.

[0054] Step 3: obtaining a digital elevation model corresponding to the map tile to be rendered and its adjacent map tiles, wherein the digital elevation model is used to represent the undulating form of the ground elevation;

[0055] The terrain of adjacent map tiles will affect the shadow of the map tile to be rendered, mainly because the ground elevations of adjacent map tiles are different, which in turn causes different light blocking effects. Therefore, this embodiment needs to obtain the digital elevation model corresponding to all map tiles in the texture image to determine the impact of the terrain of adjacent map tiles on the shadow of the map tile to be rendered, thereby improving the accuracy of shadow rendering.

[0056] Step 4: Render the texture map to an off-screen buffer of a graphics processor, obtain a height map texture buffer object corresponding to the texture map according to the digital elevation model, and calculate a corresponding normal map texture buffer object according to the height map texture buffer object;

[0057] This embodiment needs to establish a mapping relationship in advance so that the tiled raster data set can be used by the graphics processing unit GPU to calculate the texture buffer. After the mapping relationship is established, the texture map is rendered to the off-screen buffer FBO of the graphics processing unit GPU. The graphics processing unit GPU obtains the height map texture buffer object corresponding to the texture map based on the digital elevation model corresponding to the texture map, and calculates the normal based on the height map texture buffer object to obtain the corresponding normal map texture buffer object, so as to determine the lighting range and shadow distribution on the map tile to be rendered based on the height map texture buffer object and the normal map texture buffer object.

[0058] Step 5: Set a simulated light source, and generate a lighting texture rendering image corresponding to the map tile to be rendered according to the normal map texture buffer object and based on the Monte Carlo method, wherein the lighting texture rendering image is used to represent the equivalent lighting range and shadow distribution of the map tile to be rendered under the simulated light source;

[0059] In this embodiment, generating a lighting texture rendering image corresponding to a map tile to be rendered based on the height map texture buffer object and the normal map texture buffer object and based on the Monte Carlo method specifically includes:

[0060] Step 51, iterating according to a preset number of times, each iteration includes the following steps: randomly determining a point light source in the simulated light source, constructing a light from the point light source to the map tile to be rendered along the direction from the point light source to the pixel corresponding to the map tile to be rendered, and performing fragment coloring on each pixel under the action of the light according to the height map texture buffer object and the normal map texture buffer object;

[0061] It can be understood that the simulated light source in this embodiment is a circular surface light source, which is used as a virtual sun. Figure 4 As shown, when a surface light source illuminates a three-dimensional surface, two different types of shadow areas will be generated. The umbra area is completely dark, and the penumbra area is partially illuminated. The closer to the umbra area, the weaker the light. For a more beautiful visual presentation, this embodiment enlarges the radius of the imaginary sun, so that the penumbra area of ​​the final result appears larger. That is, the radius of the simulated light source is greater than the radius of the sun. For example, the radius of the simulated light source can be 67541100 kilometers.

[0062] Figure 5 A schematic diagram of randomly selecting a point light source for an iteration is shown. After the point light source is randomly selected, the light from the point light source to the map tile to be rendered is constructed along the direction from the point light source to the pixel point corresponding to the map tile to be rendered. According to the height map texture buffer object and the normal map texture buffer object corresponding to each map tile in the texture image, each pixel point under the action of the light is colored by the fragment, and the shadow grayscale image corresponding to this iteration can be obtained.

[0063] Figure 6 A schematic diagram of randomly selecting a point light source for another iteration is shown, and the iterative process is the same as the aforementioned iterative process, which will not be repeated here.

[0064] Step 51: Blend the results of each iteration to obtain a lighting texture rendering corresponding to the map tile to be rendered.

[0065] like Figure 7As shown, this embodiment is based on the Monte Carlo method, randomly selects point light sources for multiple iterations, and obtains shadow grayscale images corresponding to the iterations respectively, and then mixes the iteration results to obtain the lighting texture rendering corresponding to the map tile to be rendered, and then calculates the equivalent lighting range and shadow distribution projected by the simulated light source on the ground. This embodiment obtains the lighting texture rendering after mixing the iteration results.

[0066] Among them, the number of iterations can be set according to actual conditions. The more iterations, the greater the amount of calculation, but the higher the accuracy. The more iterations, the smaller the amount of calculation, but the lower the accuracy. In this embodiment, the number of iterations is 128 times.

[0067] Step 6: Merge the satellite rendering image and the light texture rendering image to obtain a final rendering image of the map tile to be rendered.

[0068] like Figure 8 As shown, after obtaining the lighting texture rendering of the map tile to be rendered, the corresponding satellite rendering and the lighting texture rendering are merged to obtain the final rendering, thus completing the shadow rendering process.

[0069] To sum up, the shadow rendering method and device based on the Monte Carlo method described in this embodiment simulates the sun by setting a simulated light source, and generates a lighting texture rendering image of the map tile to be rendered under the simulated light source based on the Monte Carlo method. Finally, the satellite rendering image and the lighting texture rendering image of the tile to be rendered are merged to complete the shadow rendering of the map tile to be rendered, thereby improving the display effect of the satellite image. Users can also quickly identify the terrain, such as hilly areas, based on the shadow-rendered image.

[0070] Based on the above technical solution, this embodiment also proposes a shadow rendering device based on the Monte Carlo method, such as Fig. 9 As shown, including:

[0071] An acquisition unit is used to acquire a map tile to be rendered and its corresponding satellite rendering image; and to acquire a digital elevation model corresponding to the map tile to be rendered and its adjacent map tiles, wherein the digital elevation model is used to represent the undulating form of the ground elevation;

[0072] A splicing unit, used for acquiring all adjacent map tiles of the map tile to be rendered according to the position information of the map tile to be rendered, and splicing the map tile to be rendered and its adjacent map tiles to obtain a texture map;

[0073] A graphics processing unit, configured to render the texture map into an off-screen buffer of a graphics processor, obtain a height map texture buffer object corresponding to the texture map according to the digital elevation model, and calculate a corresponding normal map texture buffer object according to the height map texture buffer object;

[0074] A rendering unit, used to set a simulated light source, generate a lighting texture rendering image corresponding to the map tile to be rendered according to the normal map texture buffer object and based on the Monte Carlo method, wherein the lighting texture rendering image is used to represent the lighting range and shadow distribution of the map tile to be rendered under the simulated light source;

[0075] The merging unit is used to merge the satellite rendering image and the light texture rendering image to obtain a final rendering image of the map tile to be rendered.

[0076] It can be understood that since the shadow rendering device based on the Monte Carlo method described in the embodiment of the present invention is a device for implementing the shadow rendering method based on the Monte Carlo method described in the embodiment, for the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method.

Claims

1. A shadow rendering method based on the Monte Carlo method, characterized in that: The following steps are involved: Get the map tiles to be rendered and their corresponding satellite renderings; Acquire all adjacent map tiles of the map tile to be rendered according to the position information of the map tile to be rendered, and obtain a texture map after splicing the map tile to be rendered and its adjacent map tiles; Obtaining a digital elevation model corresponding to the map tile to be rendered and its adjacent map tiles, wherein the digital elevation model is used to represent the undulating form of ground elevation; Rendering the texture map to an off-screen buffer of a graphics processor, obtaining a height map texture buffer object corresponding to the texture map according to the digital elevation model, and calculating a corresponding normal map texture buffer object according to the height map texture buffer object; Setting a simulated light source, generating a lighting texture rendering image corresponding to the map tile to be rendered according to the height map texture buffer object and the normal map texture buffer object and based on the Monte Carlo method, wherein the lighting texture rendering image is used to represent the lighting range and shadow distribution of the map tile to be rendered under the simulated light source; The satellite rendering image and the light texture rendering image are combined to obtain a final rendering image of the map tile to be rendered.

2. The Monte Carlo shadow rendering method according to claim 1, wherein: Generating a lighting texture rendering image corresponding to a map tile to be rendered according to the height map texture buffer object and the normal map texture buffer object based on the Monte Carlo method specifically includes: Iterate according to a preset number of times, each iteration comprising the following steps: randomly determine a point light source in the simulated light source, construct a light from the point light source to the map tile to be rendered along the direction from the point light source to the pixel point corresponding to the map tile to be rendered, and perform fragment coloring on each pixel point under the action of the light according to the height map texture buffer object and the normal map texture buffer object; The results of each iteration are mixed to obtain the lighting texture rendering corresponding to the map tile to be rendered.

3. The Monte Carlo shadow rendering method according to claim 1 or 2, characterized in that: The radius of the simulated light source is greater than the radius of the sun.

4. The Monte Carlo-based shadow rendering method according to claim 3, wherein: The radius of the simulated light source is 67541100 kilometers.

5. The Monte Carlo-based shadow rendering method according to claim 2, wherein: The preset number of times is 128 times.

6. The Monte Carlo-based shadow rendering method according to claim 1, wherein: The step of obtaining the map tile to be rendered and the corresponding satellite rendering image thereof specifically includes: Acquire the full amount of data, and slice the satellite images corresponding to the full amount of data to obtain map tiles and their corresponding satellite renderings; Get the map tile to be rendered and its corresponding satellite rendering according to the location information.

7. The Monte Carlo-based shadow rendering method according to claim 6, wherein: Satellite images are sliced ​​based on the Mercator projection to obtain map tiles and their corresponding satellite renderings.

8. The Monte Carlo-based shadow rendering method according to claim 1, wherein: The digital elevation model is packaged using the MapTiler standard.

9. A shadow rendering device based on the Monte Carlo method, characterized in that: include: An acquisition unit, used to acquire the map tile to be rendered and its corresponding satellite rendering; and obtaining a digital elevation model corresponding to the map tile to be rendered and its adjacent map tiles, wherein the digital elevation model is used to represent the undulating form of ground elevation; A splicing unit, used for acquiring all adjacent map tiles of the map tile to be rendered according to the position information of the map tile to be rendered, and splicing the map tile to be rendered and its adjacent map tiles to obtain a texture map; A graphics processing unit, configured to render the texture map into an off-screen buffer of a graphics processor, obtain a height map texture buffer object corresponding to the texture map according to the digital elevation model, and calculate a corresponding normal map texture buffer object according to the height map texture buffer object; A rendering unit, used to set a simulated light source, and generate a lighting texture rendering image corresponding to the map tile to be rendered based on the height map texture buffer object and the normal map texture buffer object and based on the Monte Carlo method, wherein the lighting texture rendering image is used to represent the lighting range and shadow distribution of the map tile to be rendered under the simulated light source; The merging unit is used to merge the satellite rendering image and the light texture rendering image to obtain a final rendering image of the map tile to be rendered.

10. The Monte Carlo method-based shadow rendering device according to claim 9, characterized in that: The rendering unit is specifically used for: Iterate according to a preset number of times, each iteration comprising the following steps: randomly determine a point light source in the simulated light source, construct a light from the point light source to the map tile to be rendered along the direction from the point light source to the pixel point corresponding to the map tile to be rendered, and perform fragment coloring on each pixel point under the action of the light according to the height map texture buffer object and the normal map texture buffer object; The results of each iteration are mixed to obtain the lighting texture rendering corresponding to the map tile to be rendered.

Images