Google Maps - Quadtree tiling system

So Google and other online mapsite using a tiling system to transfer large images.

These images are cut into smaller ones, based on a nested hierachy.... known as Quadtree. Good explaination here


Google use q,r,t,s (0-3) to denote one of 4 corners of a tile.

So to find your location run this Python code....




Run it like this:

python googletiles.py 17 -43.525 172.616

Spherical Mercator (ESPG:900913) coordinates for lat/lon:
(19215525.222771712, -5392226.689463486)
17/128383/47899 ( TileMapService: z / x / y )
Google: 128383 83172
Quadkey: 31311030123311311 ( 14851095925 )


Substitute the QUADKEY values as follows
0=q
1=r
2=t
3=s

Then type that list of letters into this page...




Here's an example for Christchurch, NZ
http://pallit.lhi.is/bigice/makeme.php?startPic=tsrsrrqsqrtssrrsrr&hTiles=14&vTiles=14


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Other useful info on tiling

cut your own tiles - x,y info
http://makemeamap.com/cgi-bin/mercator4.pl

view tiles on one page
http://pallit.lhi.is/bigice/bigpic.html

how it works
http://www.maptiler.org/google-maps-coordinate-system-projection-epsg-900913-3785/

overlay on web your own image and create the tiles for it
http://open.atlas.free.fr/GMapsTransparenciesImgOver.php

use python to create a local cache of WMS tiles
http://www.tilecache.org/