1. Basic concepts:
World Wind Tile Structure: refers to the WW tile data structure.
After the default browser texture data stored in the \ Cache \ Earth \ Images \ NASA Landsat Imagery \ NLT Landsat7 (Visible Color), and elevation data as tiered storage, downloaded from the server image to JPG format, 512 * 512 pixels, the download is complete converted to DDS format, DTX3 compression, the space occupied will increase more than doubled, but can save 50% of the memory is said to run. Temporary files downloaded suffix jpg.tmp, after downloading an error will be more than a 0 byte file jpg.txt.
Borders data stored in the Cache \ Earth \ Boundaries \ Country Political Boundaries, for the PNG image format, more detailed boundaries now only the US: Cache \ Earth \ Boundaries \ US State Political Boundaries, are 512 * 512 pixel PNG image transfer for the DDS format
DEM data stored in the Cache \ Earth \ SRTM suffix .bil.
2. The class includes:
纹理：QuadTileset，QuadTile，ImageStore，GeoSpatialDownloadRequest(WorldWind.Renderable)
DEM高程：TerrainAccessor，NltTerrainAccessor，TerrainTile，GeoSpatialDownloadRequest(WorldWind.Net)
QuadTile is a quad-tree data structure tile, defined the quad-tree, the paste texture on the quad-tree tiles, and can be added to the quad-tree height.
Figure 1 texture
FIG 2 DEM elevation obtain