Terrain data

Terrain data are data that represent the ups and downs on the Earth surface, i.e., data containing elevation information. Digital elevation model (DEM) is a continuous representation of spatial variation in elevation. It is a special data model of the DatasetGrid type. The value in every grid is an elevation value, and is represented with a standard color, which is helpful for merging adjacent DEM images.

SuperMap Realspace services support preprocessing DEM and Grid elevation data to generate 3D terrain cache data and publish them. Elevation model are divided into levels and blocks based on a global grid division model. A cache directory is generated accordingly and a SCT file (*.sct) is generated at the same time. This SCT file contains detailed description on the generated cache, such as the number of cache levels, the cached geographical extent, the cache file type, etc. When loading cached terrain data in a realspace environment, users can load cached terrain data by loading the corresponding index file. Terrain data are added on the 3D globe in a 3D scene according to the coordinate information, so that the globe surface can simulate the ups and downs of the Earth surface realistically.

For transmitting terrain data, SuperMap 3D adopts the following strategies to reduce the transmitted data volume and improve the efficiency of data transmission:

1. The sample points are increased during dividing terrain data to increase the data information volume of each tile. The original tiles are packaged into a big file to decrease the number of tiles and the number of files on the disk. The times of transmission are then reduced, and data with larger size can be published. In addition, the time for creating the cache can also be reduced, and the efficiency of displaying and viewing on a client is improved;
2. Compression and transmission. A server compresses data and then transmits them. The data are then downloaded and decompressed on the client before they are used.