[OpenLayers-Users] Questions: Projections, Google, Yahoo, etc

[Trond Michelsen]

On Tue, Feb 20, 2007 at 08:15:39AM +0000, Jon Blower wrote:
> Here's the same thing in Mercator: note that the bounding box is the
> same (i.e. expressed in decimal degrees) but the projection has
> changed to EPSG:41001:

Whoa! I'm pretty sure that's incorrect behaviour.

> From the server's point of view, the key is to calculate, for a given
> BBOX and image width/height, the lat-lon coordinates of each pixel in
> the image.  My (Python) code to do this is at:
> http://www.resc.rdg.ac.uk/trac/ncWMS/browser/trunk/web/WEB-INF/jython/grids.py.
> 
> From a tiling client's point of view, the key is to calculate, for a
> given image tile, the correct BBOX in decimal degrees.

Maybe I'm misunderstanding you here, but the WMS spec states that the
coordinates used in BBOX are in the coordinate system defined by the
CRS parameter. So, when you're using a Mercator projection, the
BBOX-units is normally in meters.

-- 
Trond Michelsen