[Proj] Post-projection affine transformations?

[Frank Warmerdam]

Michal Migurski wrote:
> Hello,
> 
> I'm trying to determine whether Proj parameters can express an arbitrary
> post-projection affine transformation, e.g. shear or rotation. I've looked
> at the +towgs84 parameter but this doesn't seem to be a good fit. Is it
> possible to transform a projection, for example to flip a mercator map
> upside-down? I'm rendering images with Mapnik which seems to use Proj
> internally.


Mike,

Generally speaking I'm not aware of a way of doing arbitrary post
projection affine transformations as part of the projection process
via proj commandline switches.

However, "proj trunk" does add new commandline arguments for switching
around the axes that might be sufficient for your mirroring needs.  If
you can build with trunk, you could try adding something like:

   +axis=esu

which means that the X axis is "easting" the Y axis is "southing"
and the Z axis is "up".

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent