Only 4 Steps to Make a Shading Map!

Shading map is the most common form to express the terrain. It shows the ups and downs of the earth's surface through shadow and color gradients, with a good sense of three-dimensional. The global shading map provided in SuperMap has clear terrain and light color matching. Users can directly use it as the base map and overlay other data on it. How to make such a picture? Here is a detailed introduction.

1.Data download and preprocessing

The global terrain data comes from the SRTM DEM elevation data in the geospatial data cloud website. The address is https://www.gscloud.cn/

Vegetation data from USGS website, USGS https://landcover.usgs.gov/global_ climatology.php

2. Expression of marine topography

The ocean is the basic part of the global shading map, and the degree of concern is not high compared with the land. Therefore, the ocean part does not need to show the terrain details in detail, only needs to show the overall changes of the seabed topography. Here we choose the layered color method to express.

2.1 Extract isosurface

The isosurface is extracted from the global terrain data. The isosurface distance is set to 1000m, and the B-spline method with a smooth coefficient of 2 is used to smooth the isosurface.

2.2 Making single value thematic map

The single value thematic map is made for the extracted isosurface, and the color is set for the isosurface of different height values, so that the altitude changes from low to high to the blue of dark to light, so as to simulate the real ocean color.

2.3 Output image dataset

Due to the slow loading of isosurface layer, this layer can be output to image dataset, which can greatly speed up the display efficiency.

3. Expression of land topography

3.1 Cropped land topography

The DEM of land terrain is cut out by using land surface data set.

3.2 Generate shadow data

The hill shadow data is obtained by calculating the 3D shading map of the land DEM data.

3.3 Terrain simplification

Although the terrain expression covering the global land can show all the terrain in an all-round way, at the same time, it will lead to unclear map focus and lack of sense of hierarchy. As the global shading map of the base map, the topography of vegetation, cultivated land and water system is relatively important, with a high degree of concern, while the terrain of areas such as glaciers and wastelands is complex and generally does not have the superposition of thematic elements, which can not be expressed directly. For the areas covered by urban land, the additional elements that may be superposed later are relatively dense, such as road network, railway, POI points, etc., and the base map of terrain as auxiliary expression will interfere with the expression of these elements, or choose not to express. Using the method of data update, the snow mountain, wasteland and urban land in the shadow data are set to null.

3.4 Terrain superposition

The land shadow data can be superimposed on the top of the ocean, and in order to avoid the empty terrain from the bottom ocean, a layer of land surface data can be superimposed between the land shadow data and the ocean layer.

4. Superimposed vegetation

Overlay the vegetation grid data on the top of the terrain data and set a certain degree of transparency. It should be noted that when the scale of the map is small, the terrain is relatively fuzzy, so the vegetation does not need to set a high degree of transparency. When the scale is large, the transparency of the vegetation needs to be higher to better display the terrain below. This effect can be achieved by setting a higher degree of transparency for the vegetation Set the display scale to achieve.

Here, the global shading map is finished. If you have administrative boundaries, rivers, roads, POI points and other data, you can directly overlay them for display

Isn't it simple? Come and have a try!

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