[Mapserver-users] Polar stereographic projection misbehaviour

[Frank Warmerdam]

Sebastian Albrecht wrote:
> Hello,
> 
> I have a shapefile containing coastlines of the Antarctica projected
> in: "proj=stere,ellps=WGS84,lat_ts=-75,south,lat_0=-90"
> 
> Further I have a shapefile containing only latlong coordinates as
> shiptracks and a graticule layer using the GRID feature.
> 
> The coastlines are displayed correctly but there are often missing
> parts of the other layers. The latlong tracks are just cut off at some
> latitude coordinate and the graticule is only displayed down to -60 or
> -70 degrees latitude.
> 
> I added some logging code to the map_project.c file and found out
> those missing values are not even send to the projection library. It
> seems to me Mapserver somehow does not know what to do with the given
> extent and thinks several values are not located in the area to be
> displayed?!
> 
> Is there a solution for this problem? I use Mapserver 4.0 and PROJ
> 4.4.7.

Sebastian,

I assume you are trying to show things in polar stereographic.  The problem
is (presumably) that when the region is converted into lat/long to query
the lat/long file, the resulting bounding rectangle is mixed up since
the pole will be a very screwy region in lat/long.  My suggestion would be
to reproject your lat/long data into polar stereographic ahead of time
to keep things well behaved in mapserver.  You could use ogr2ogr to do
the reprojection if you like, or perhaps shpproj though I don't really maintain
that.

Best regards,

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