| TileStache.Goodies.Proj4Projection | index |
Projection that supports any projection that can be expressed in Proj.4 format.
The projection is configured by a projection definition in the Proj.4
format, the resolution of the zoom levels that the projection should
support, the tile size, and a transformation that defines how to tile
coordinates are calculated.
An example, instantiating a projection for EPSG:2400 (RT90 2.5 gon W):
Proj4Projection('+proj=tmerc +lat_0=0 +lon_0=15.80827777777778 +k=1'
+' +x_0=1500000 +y_0=0 +ellps=bessel +units=m +no_defs',
[8192, 4096, 2048, 1024, 512, 256, 128, 64, 32, 16, 8, 4, 2, 1],
transformation=Transformation(1, 0, 0, 0, -1, 0))
This example defines 14 zoom levels, where each level doubles the
resolution, where the most zoomed out level uses 8192 projected units
(meters, in this case) per pixel. The tiles are adressed using XYZ scheme,
with the origin at (0, 0): the x component of the transformation is 1, the
y component is -1 (tile rows increase from north to south). Tile size
defaults to 256x256 pixels.
The same projection, included in a TileStache configuration file:
"example":
{
"provider": {"name": "mapnik", "mapfile": "examples/style.xml"},
"projection": "TileStache.Goodies.Proj4Projection:Proj4Projection('+proj=tmerc +lat_0=0 +lon_0=15.80827777777778 +k=1 +x_0=1500000 +y_0=0 +ellps=bessel +units=m +no_defs', [8192, 4096, 2048, 1024, 512, 256, 128, 64, 32, 16, 8, 4, 2, 1], transformation=Transformation(1, 0, 0, 0, -1, 0))"
}
"Module:Class()" syntax described in http://tilestache.org/doc/#projections.
For more details about tiling, projections, zoom levels and transformations,
see http://blog.kartena.se/local-projections-in-a-world-of-spherical-mercator/
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