Polar Stereographic

[Dominic Lowe]

Hi All,

This query is probably more to do with map projections than with
Mapserver, depending on where I'm going wrong...

I'm trying to display Polar Stereographic maps (of Europe) in Mapserver.
I can successfully display the maps, but something is not right as they
don't reproject properly to other coordinate systems (eg epsg:4326) - by
this I mean they reproject but the map will appear distorted in the
wrong part of the lat lon world.

So anyway I think that I've just created an arbitary projection and got
them to display somehow. What I'd like to do is display them in an epsg
compliant Polar Stereographic...

I've added a line to the epsg file:
<9810> +proj=stere +lat_ts=90 +lat_0=90 +lon_0=0 +k_0=1.0 +x_0=0 +y_0=0

this is based on the information here:
http://www.remotesensing.org/geotiff/proj_list/polar_stereographic.html
North Pole (NatOriginLat > 0): *

  +proj=stere +lat_ts=/Latitude at natural origin/
              +lat_0=90
              +lon_0=/Longitude at natural origin/
              +k_0=/Scale factor at natural origin/ (normally 1.0)
              +x_0=/False Easting/
              +y_0=/False Northing/

*So I think by setting lat_ts to 90 I've assumed that the "projected
image" is tangential to the north pole.

So then I've tried different methods for converting the lat lon
coordinates into Eastings Northings to be used in a world file to
accompany the image. If the 9810 definition is ok then I think this is
where I'm going wrong - there seem to be several possible coordinate
systems that lay claim to the name 'Polar stereographic' - (eg UPS - is
that the same as vanilla Polar?) and I'm not sure which one relates to
epsg:9810 that I 'think' I've defined.

Anyway, I'd very much appreciated it if anyone has any experience of
using Polar Stereographic in Mapserver and could help clarify these issues.

Regards

Dominic