World Wind Map Tile System
From Wikiteer
The World Wind Map Tile System is a way of serving images from a NASA World Wind image server.
World Wind uses map imagery in the Plate Carree projection (aka geographic projection).
For performance reasons, World Wind stores multiple copies of the same map in successively higher resolutions. Each additional layer quadruples the number of tiles. Thus the tile size, in degrees (LevelTileSizeDegrees), halves with each successive level.
Each tile is a 512x512 pixel square that can be stored in any image format such as PNG, JPG, DDS, etc.
The coordinate system for World Wind starts at the lower left corner.
For an example
The base layer divides the world into 36x36 degree pieces starting at level 0.
| level 0 | 36 degrees | 50 tiles (10x5) |
| level 1 | 18 degrees | 200 tiles (20x10) |
| level 2 | 9 degrees | 800 tiles (40x20) |
| level 3 | 4.5 degrees | 3200 tiles (80x40) |
| level n | 36/2^n degrees | 50*4^n tiles (Failed to parse (Can't write to or create math temp directory): 10*2^n
xFailed to parse (Can't write to or create math temp directory): 5*2^n ) |
- x=(long+180)/LevelTileSizeDegrees
- y=(lat+90)/LevelTileSizeDegrees
http://www.ceteranet.com/nww-tile-struct.pdf
