Map making with three-dimensional effect

Recently, users often ask, can you make undulating topographic maps with SuperMap desktop software? The answer is of course yes: yes! Generally, I would recommend users to use DEM to generate orthographic 3D images or 3D shading maps, but what is the specific difference between the two, which is better? Today I will use an example to explain it briefly.

Use sample data: Jin Jing demonstration data provided in SuperMapiDesktop. As the provided Jin Jing data is latitude and longitude, it is suggested to convert the data into projection first to ensure the unity of grid X, Y and Z values.

1.

"Orthographic 3D Image" function, which is used to generate orthographic 3D images. In the process of shooting aerial images, the camera can not be guaranteed to be absolutely horizontal at any time, so the obtained images may be tilted; In addition, due to the inherent error of imaging mode, it is necessary to correct the image to eliminate all kinds of deformation. The corrected image is an orthogonal three-dimensional image.

The essence of orthophoto map is the process of correcting orthophoto map through the elevation of adjacent grids and using digital differential correction technology to get the reasonable sunshine intensity at the current point.

For example, Figure 1 shows the original raster image of a certain area in Jin Jing, and Figure 2 shows the generated orthographic 3D image.

Orthophoto three-dimensional image can achieve the effect of undulating topographic map, but when DEM generates orthophoto three-dimensional: ① the angle of sunlight cannot be set, so the system default can only be used; ② The result data set is an image data set, and its color table cannot be set. Although the color table can be set when generating the orthographic 3D image, as shown in Figure 3, the result data set has been applied, and it is troublesome to regenerate the orthographic 3D image if adjustment is needed.

Fig. 3 schematic diagram of dialog box for generating 3D image of orthophoto.

So, can you solve these problems by using 3D shading? Let's take a look.

2.

Three-dimensional shading map is a grid map that reflects the terrain fluctuation by simulating the shadow of the actual surface. By illuminating the map with an imaginary light source and combining the slope and aspect information obtained from raster data, the gray value of each pixel is obtained. The slope facing the light source has the highest gray value, while the slope facing the light source has a lower gray value, which is a shadow area, thus vividly representing the actual landform and terrain of the grid.

Three-dimensional shading map is mainly used for display. Using the function of analysis-surface analysis-three-dimensional shading map, raster data with three-dimensional effect is generated by DEM, as shown in Figure 4. The main parameters of this function are set as follows:

Their default values are 3 15 and 45, respectively, and the effect is the sun position in winter afternoon in Beijing. If you want the midday sunshine effect in summer of beijing, you can change it to 225,90, and other areas can adjust it according to the actual situation.

Fig. 4 Schematic diagram of 3D shadow dialog box

The next step is the superposition effect rendering of the generated mountain shadow data and the original DEM. The two are superimposed in the same map window, with the original DEM layer in the upper layer and the mountain shadow data in the lower layer. Then the transparency and brightness of the original DEM layer are set, and the DEM layer can choose the appropriate color table according to the needs, so that it can easily create beautiful, detailed and three-dimensional topographic maps. As shown in fig. 5.

In different application scenarios, in order to achieve the best mapping effect, it is necessary to constantly adjust parameters, such as the transparency and brightness of raster layers. After that, you can continue to add other layers (such as land use type map, road and river layer) on it, which can further enrich the map information. The following figure shows the effects of different grading and transparency settings:

The classification in Figure 6 is realized by making the segmented thematic map of the original DEM.

As shown in Figure 7, it is a map with three-dimensional shading map as the base map and superimposed information such as roads and towns.

The raster dataset has more controllability than the image dataset, such as setting the color table, making thematic maps, and setting the transparency and brightness of layers. Therefore, when drawing, the raster dataset is used as the base map, and then some other feature layers are superimposed, so the display effect of the map is better. Generating a map cache and publishing the map for browsing, performance is not a problem.