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

[Rich Shepard]

On Thu, 18 Feb 2010, Markus Metz wrote:

> 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.

Markus,

   Yes. That's what I did the first time.

> 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).

   This is what I tried to do. I used the location wizard in the wxPython
GUI, set the false easting to 400000.00000 meters and the resolution as 1.0
(leaving the bounds unspecified). I thought that would do the job because --
for the new location -- PROJ_INFO and PROJ_UNITS are:

name: Lambert Conformal Conic
proj: lcc
datum: nad83
ellps: grs80
lat_1: 43
lat_2: 45.5
lat_0: 41.45
lon_0: -120.5
x_0: 400000
y_0: 0
no_defs: defined
nadgrids: WO

unit: meter
units: meters
meters: 1

   This appears to me to be correct. However, ...

> 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?

   This is where I'm hung up.

Thanks,

Rich