[GRASS5] GRASS 5.3/5.7, GDAL and southern hemisphere

[Markus Neteler]

Hello Paul,

thanks for your answers.

On Thu, Sep 25, 2003 at 03:26:53PM +0100, Paul Kelly wrote:
> On Thu, 25 Sep 2003, Markus Neteler wrote:
> > WARNING: [tuc6] in mapset [tucuman] - in different zone [-4] than current
> >          region [4]

So - it appears that the colleague has TM and not UTM (so partially
solved). But:
 
> Looking into it further, it appears r.in.gdal will set the zone in the
> raster header to a negative value if the region is in the southern
> hemisphere. But g.setproj will never create a negative zone in the WIND
> file (which has the same format as a raster/CELL header), and indicates
> that it is in the southern hemisphere by putting south: defined in the
> PROJ_INFO file.
>
> pj_get_kv() will accept either south: defined or a negative zone number in
> the PROJ_INFO. I suspect if you created the location using r.in.gdal it
> would put a negative zone number in the WIND, and d.rast would be
> happy.

I assume that it is always happy when the map zone number matches
the overall defined zone number.

> To summarise: this inconsistency could be fixed either in r.in.gdal or
> g.setproj and I'm not sure which would be more appropriate as I don't
> understand the significancy of being in the southern hemisphere for the
> UTM projection. Maybe somebody could explain this.

Maybe Hamish can help?
 
> Temporary workaround: make sure the zone in the cellhd and WIND are the
> same---I'm not sure if they're actually used for anything these days
> anyway.

Will do, thanks.

Markus