class GlobalGeodetic(object):
"""
TMS Global Geodetic Profile
---------------------------
Functions necessary for generation of global tiles in Plate Carre projection,
EPSG:4326, "unprojected profile".
Such tiles are compatible with Google Earth (as any other EPSG:4326 rasters)
and you can overlay the tiles on top of OpenLayers base map.
Pixel and tile coordinates are in TMS notation (origin [0,0] in bottom-left).
What coordinate conversions do we need for TMS Global Geodetic tiles?
Global Geodetic tiles are using geodetic coordinates (latitude,longitude)
directly as planar coordinates XY (it is also called Unprojected or Plate
Carre). We need only scaling to pixel pyramid and cutting to tiles.
Pyramid has on top level two tiles, so it is not square but rectangle.
Area [-180,-90,180,90] is scaled to 512x256 pixels.
TMS has coordinate origin (for pixels and tiles) in bottom-left corner.
Rasters are in EPSG:4326 and therefore are compatible with Google Earth.
LatLon <-> Pixels <-> Tiles
WGS84 coordinates Pixels in pyramid Tiles in pyramid
lat/lon XY pixels Z zoom XYZ from TMS
EPSG:4326
.----. ----
/ \ <-> /--------/ <-> TMS
\ / /--------------/
----- /--------------------/
WMS, KML Web Clients, Google Earth TileMapService
"""
def __init__(self, tileSize = 256):
self.tileSize = tileSize
def LatLonToPixels(self, lat, lon, zoom):
"Converts lat/lon to pixel coordinates in given zoom of the EPSG:4326 pyramid"
res = 180 / 256.0 / 2**zoom
px = (180 + lat) / res
py = (90 + lon) / res
return px, py
def PixelsToTile(self, px, py):
"Returns coordinates of the tile covering region in pixel coordinates"
tx = int( math.ceil( px / float(self.tileSize) ) - 1 )
ty = int( math.ceil( py / float(self.tileSize) ) - 1 )
return tx, ty
def Resolution(self, zoom ):
"Resolution (arc/pixel) for given zoom level (measured at Equator)"
return 180 / 256.0 / 2**zoom
#return 180 / float( 1 << (8+zoom) )
def TileBounds(tx, ty, zoom):
"Returns bounds of the given tile"
res = 180 / 256.0 / 2**zoom
return (
tx*256*res - 180,
ty*256*res - 90,
(tx+1)*256*res - 180,
(ty+1)*256*res - 90
)
(from: https://github.com/brendancol/RacialDotMap/blob/master/globalmaptiles.py)