[GRASS-user] Projection Units and Values Negatively Affect r.topidx Results

[Markus Metz]

Rich Shepard wrote:
> On Thu, 18 Feb 2010, Markus Metz wrote:
>> 2) use v.in.region
>
> v.in.region out=coverage type=area
>
>> 2) get resolution in meters with g.region -m (applies only to raster 
>> map reprojection)
>
> GRASS 6.4.0svn (oregonM):/usr4/grassbase > g.region -m
> n=1735231.43724681
> s=1120657.1324816
> w=143667.18968253
> e=952979.22944945
> nsres=32.82281055
> ewres=32.82281055
> rows=18724
> cols=24657
> cells=461677668
>
>   The resolution is still in feet (or is this now seen as 32.8 meters?
Wouldn't make sense, 32.82281055 international feet are about 10.12 
meters. I guess your projection is missing the information about how to 
convert feet to meters. In proj4 lingo that would be +to_meter=0.3048. 
The problem could be that for your dem, the horizontal units are 
Planar_Distance_Units: User_Defined_Unit and not international feet 
(this problem might originate from using ESRI software to generate the 
source data but that's a wild guess and doesn't help you much).