Sean Gillies Blog

MapServer's scripting module allows users access to the program's projection capabilities. One of these is particularly useful for quick calculation of map extents. Let's say you have a world-wide dataset with a lat/long WGS84 coordinate system, and want to render it onto a Mollweide projection map. Start your interpreter, import the mapscript module, and create output and input projection objects. For the input I use the EPSG shorthand for a lat/long WGS84 coordinate system. Initialize a rectangle to the full extent of the world in units of the input projection, and transform it to output units using its project() method:

>>> import mapscript
>>> proj_out = mapscript.projectionObj('+proj=moll +lon_0=0.0')
>>> proj_in = mapscript.projectionObj('+init=epsg:4326')
>>> e = mapscript.rectObj(-180,-90,180,90)
>>> e.project(proj_in, proj_out)
0
>>> print e.minx, e.miny, e.maxx, e.maxy
-18040095.6961 -9020047.84807 18040095.6961 9020047.84807
>>>

The output values are ready to be used within your map's extent definition.