[GRASS-user] g.region - g.proj : different utm zones for same are

[Paul Kelly]

On Sun, 13 Mar 2011, TimNorwey wrote:

> Hy!
>
> I have used g.region and g.proj for showing the projection information of my
> data set.
>
> When using g.region, the current UTM zone is 0, while when using g.proj the
> UTM zone is 15. Beside, UTM zone 15 is the right one (see the picture below
> - sry for the bad quality)
>
> http://osgeo-org.1803224.n2.nabble.com/file/n6167098/both.png
>
> So why there are different outputs between this two modules or do I
> interpret something wrong?

When GRASS was originally created in the early 1980s the only co-ordinate 
system it supported was UTM, thus the zone was the only projection 
parameter that needed to be stored and it was kept alongside the region 
information in the region file. This field is still there for backwards 
compatibility but an additional copy of the zone is stored as part of the 
projection information, and this is what is actually used in any modules 
or import/export procedures that require knowledge of the projection. Thus 
it won't be a problem that the zone in the region information is incorrect 
(it would be a problem if the zone in the projection information was 
incorrect). They should normally be kept in sync though and I'm not sure 
why they wouldn't be. If you can remember how the location was originally 
created it might shed some light on it.

Paul