[GRASSLIST:3017] Re: Projection conversion help

Roger Miller rgrmill at rt66.com
Mon Jan 28 21:29:38 EST 2002

On Monday 28 January 2002 02:37, H. Fernandez wrote:

> After a lot of hours reading and searching all over the net, I think GRASS
> (and the function r.proj) is the tool I need. I install in my PC a LINUX,
> download GRASS and run many test without success. r.proj give me an error
> "input map is outside current region", even if I try to define the output
> region larger than original one. I think is because my definition of
> "mercator" projection is not correct.


To use r.proj you need to set up two locations.  The first location will hold 
your original map, which I believe you said was in UTM coordinates.  For that 
location you will need to specify the spheroid and datum for the projection 
and the UTM zone of the map.  You will also set the resolution and the 
boundaries of the default region.  Before you run r.proj you can make sure 
that your input map is in the current region by using the map to define the 
region; type "g.region rast=<your map name>".

The second location (mercator?) will hold the converted map.  You need to be 
sure that your specification for the ellipsoid, datum and projection are 
correct so that you get the right results.  I think that r.proj ignores the 
current region and just imports the file.

To run r.proj, start GRASS with the mercator location and mapset where you 
want the converted map to be stored.  Use r.proj to copy the map from the UTM 
location to your new mercator location.  After you copy the map again set the 
current region to equal the region covered by the map by typing "g.region 
rast=<your new map name>".

I hope that helps.

Roger Miller

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