Commonly used 3D renderings include the following:
Orthophoto 3D Image
The Orthophoto 3D Image generated by DEM can achieve a certain visual effect of three-dimensional terrain. As shown in Fig. 1 and Fig. 2, the 3D orthophoto has an obvious stereoscopic effect, which has a good effect on expressing regional terrain conditions and is convenient for understanding the characteristics of mountain terrain. Overlapping with other thematic information can help us carry out various Spatial Analysis, such as site selection.
The "Orthophoto 3D Image" function is used to calculate the brightness of the current point with the elevation change of the surrounding grid after the three-dimensional projection of the DEM, and then render the DEM brightness value to generate the Orthophoto 3D Image according to the specified color table and valueless color.
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| Figure 1: Raster artwork | Figure 2: Orthophoto 3D Image |
3D Hillshade Map
The 3D Hillshade Map "feature generates a 3D vignetting rendering by taking into account the angles and shadows of the grid surface illumination source. 3D Hillshade Map is a grid map that reflects the relief of the terrain by simulating the shadow of the actual surface. The gray value of each pixel is obtained by using the imaginary light source to illuminate the map and combining with the Slope Aspect information obtained by Raster Data. The gray value of the slope facing the light source is the highest, and the gray value of the slope facing away from the light source is lower, which is the shadow area, thus vividly representing the actual landform and topography of the grid. Because the mountain shadow map calculated by Raster Data has a very realistic three-dimensional effect, it is generally called 3D Hillshade Map.
3D Hillshade Map is mainly used for display. By overlaying the grid (Figure 3) with the 3D Hillshade Map (Figure 4), and then setting the transparency of the Raster Layer, you can easily create a beautiful, detailed and three-dimensional landscape map (Figure 5). In different application scenarios, in order to achieve the best drawing effect, it is necessary to constantly adjust the parameters, such as the transparency and brightness of Raster Layer. After that, you can continue to add other layers (such as Land Use type map, road and river layers) on it to further enrich Map Information.
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| Figure 3: Grid artwork | Figure 4: 3D Hillshade Map | Figure 5: Overlay effect |
When generating the 3D Hillshade Map, you need to specify the position of the imaginary light source, which is determined by the azimuth and elevation angles of the light source.
- Azimuth is used to determine the direction of the light source and is expressed in degrees. As shown in the figure below, start with the due north direction as 0 degrees, measure clockwise, and assign angle values to each direction from 0 degrees to 360 degrees, so the due north direction is also 360 degrees. Due east is 90 degrees, due south is 180 degrees, and due west is 270 degrees. The default value for azimuth is 315 degrees.
- of elevation is that angle at which the light source is til, ranging from 0 degree to 90 degrees. As shown in the figure, when the angle of elevation of the light source is 90 degrees, the light source is perpendicular to the surface of the earth. The elevation angle defaults to 45 degrees.
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When the azimuth angle of the light source is 315 degrees and the altitude angle is 45 degrees, the Relative between the light source and the ground surface is shown in the following figure.
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