World Wind Map Tile System

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The [[World Wind Map Tile System]] is a way of serving images from a [[NASA World Wind image server]].
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[[World Wind]] uses [[map imagery]] in the [[Plate Carree projection]] (aka [[geographic projection]]).
[[World Wind]] uses [[map imagery]] in the [[Plate Carree projection]] (aka [[geographic projection]]).
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For performance reasons, [[World Wind]] stores multiple copies of the same map in successively higher [[resolution]]s.  Each additional layer quadruples the number of tiles (and size).
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For performance reasons, [[World Wind]] stores multiple copies of the same map in successively higher [[resolution]]s.  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.
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.
The coordinate system for World Wind starts at the lower left corner.
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For an example
The base layer divides the world into 36x36 degree pieces starting at level 0.
The base layer divides the world into 36x36 degree pieces starting at level 0.
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*[[Image:Math01.png]]
*[[Image:Math01.png]]
*[[Image:Math02.png]]
*[[Image:Math02.png]]
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*<math>x=\\lfloor (long+180)/360 \\rfloor *10*2^n</math>
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*x=(long+180)/LevelTileSizeDegrees
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*<math>y=\\lfloor (lat+90)/180) \\rfloor *5*2^n</math>
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*y=(lat+90)/LevelTileSizeDegrees
http://www.ceteranet.com/nww-tile-struct.pdf
http://www.ceteranet.com/nww-tile-struct.pdf
http://issues.worldwind.arc.nasa.gov/confluence/download/attachments/394/world+wind+tile+systemt.gif
http://issues.worldwind.arc.nasa.gov/confluence/download/attachments/394/world+wind+tile+systemt.gif
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[[category:standards]]

Current revision as of 13:24, 29 October 2006

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 )

  • Image:Math01.png
  • Image:Math02.png
  • x=(long+180)/LevelTileSizeDegrees
  • y=(lat+90)/LevelTileSizeDegrees

http://www.ceteranet.com/nww-tile-struct.pdf

world+wind+tile+systemt.gif

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