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

[Markus Metz]

As evident from the attached pdfs in your previous post, all source data 
have International feet (= 0.3048 meters) as units. That means, the 
location where you import all the stuff must have international feet as 
horizontal units.

if you want to convert the vertical units of your dem from international 
feet to meters (because "The final processing step involved converting 
the z-units from meters to feet and converting back to an integer 
grid."), that could be done with

r.macalc "<DEM_in_meters> = <DEM_in_feet> * 0.3048"

, preferably in the source location.

If you want to have everything with meters as horizontal unit, the 
target location *must* have meters as unit. That also means that false 
easting for the target location must be 400000 meters when defining it 
(for the source location, it's 1,312,335.958 feet).

When reprojecting maps from the feet location to the meters location, 
the SOP would be to
1) set the region to the extends of the map to be reprojected
2) use v.in.region
2) get resolution in meters with g.region -m (applies only to raster map 
reprojection)
3) go to the target location, reproject the output of v.in.region
4) set the resolution for raster map reprojection
5) reproject whatever needs to be reprojected

These steps should also be described in the respective manuals.

HTH,

Markus M


Rich Shepard wrote:
> On Thu, 18 Feb 2010, Rich Shepard wrote:
>
>> GRASS 6.4.0svn (oregonM):/usr4/grassbase > r.proj in=demNW loc=Oregon
>> mapset=PERMANENT out=demNW10 method=bilinear res=10.0 --o
>> Input Projection Parameters:  +proj=lcc +lat_1=43 +lat_2=45.5 
>> +lat_0=41.75
>> +lon_0=-120.5 +x_0=400000.00000000 +y_0=0 +no_defs +a=6378137
>> +rf=298.257222101 +nadgrids=/usr/local/grass-6.4.0svn/etc/nad/WO
>> Input Unit Factor: 0.3048
>> Output Projection Parameters:  +proj=lcc +lat_1=43 +lat_2=45.5 
>> +lat_0=41.45
>> +lon_0=-120.5 +x_0=400000 +y_0=0 +no_defs +a=6378137 +rf=298.257222101
>> +nadgrids=/usr/local/grass-6.4.0svn/etc/nad/WO
>> Output Unit Factor: 1
>> ERROR: Input raster map is outside current region
>
>   More information:
>
>   From the input location:
>
> GRASS 6.4.0svn (Oregon):/usr4/grassbase > g.region rast=demNW -p
> projection: 99 (Lambert Conformal Conic)
> zone:       0
> datum:      nad83
> ellipsoid:  grs80
> north:      1735231.43724681
> south:      1120657.1324816
> west:       143667.18968253
> east:       952979.22944945
> nsres:      32.82281055
> ewres:      32.82281055
> rows:       18724
> cols:       24657
> cells:      461677668
>
>   From the destination location:
>
> GRASS 6.4.0svn (oregonM):/usr4/grassbase > g.region -p
> projection: 99 (Lambert Conformal Conic)
> zone:       0
> datum:      nad83
> ellipsoid:  grs80
> north:      1735231.43724681
> south:      1120657.1324816
> west:       143667.18968253
> east:       952979.22944945
> nsres:      32.82281055
> ewres:      32.82281055
> rows:       18724
> cols:       24657
> cells:      461677668
>
>   Since they are identical, what could trigger the error message, "Input
> raster map is outside current region" other than the unit factors, and
> that's what I'm trying to change (from feet to meters).
>
> Rich
> _______________________________________________
> grass-user mailing list
> grass-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-user
>