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I would like to create a world map "upside down", with the south on top (in Mapnik).

Can I take an existing projection string, e.g. Robinson projection

+proj=robin +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs

and flip/mirror it so the north points down?

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1 Answer 1

up vote 4 down vote accepted

In PROJ.4 trunk, there is upcoming support for 'upside down' Mercator projections in Proj.4, which Frank explains how to use as such:

"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".

Alternatively, you could do the rotation after the projection step, which seems to be what Mapserver has implemented.

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Thanks, that gave me some pointers. Some more resources I found on the topic (and arbitrary rotations): Mapnik Ticket, Discussion, Rotating maps by transforming coords in the DB –  Flo Ledermann Feb 17 '11 at 10:10

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