pTolemy3D Tile System

pT uses map imagery in the Platte Carrée projection of the WGS84 longitude/latitude coordinates in decimal degrees (DD) with Greenwich as the central meridian.

The SRS code is "EPSG:4326"

this allows pT to take rectangular image (2x1 ratio) and map it to a sphere.

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In order satisfy the necessary LOD of the current view, map data is tiled and layered at successively higher resolutions. Each higher resolution has 64x the number of tiles, forming an 8x8 grid of the previous tile.

Each tile is 1024 pixel square jp2000 file that is internally layered 4x

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The pT coordinate system uses longitude/latitude DD values directly in the path and filename to describe both the detail level and position of each tile.

(approximation, this image does not have the correct grid lines)

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Layer	DD Width	Number Tiles	Tile Width Meters	Width of Pixel
Level 54428800	54.428800 Degrees	32 Tiles	5,836,345	224,391.95
Level 6553600	06.553600 Degrees	1,568 Tiles	729,5432	28,048.99
Level 819200	00.819200 Degrees	96,800 Tiles	91,193	86.06
Level 102400	00.102400 Degrees	6,181,128 Tiles	11,399	11.13
Level 12800	00.012800 Degrees	395,535,938 Tiles	1,425	1.39
Level 1600	00.001600 Degrees	25,312,500,000 Tiles	178	0.17