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

[Micha Silver]

Rich Shepard wrote:
> On Wed, 17 Feb 2010, Markus Neteler wrote:
>
>> I think that a change of the base unit of a location requires a new
>> location and reprojection of the data. I may be wrong, though.
>
> Markus/Hamish:
>
>   I'm missing something critical here.
>
>   I defined a new location (called oregonM) with the following projection
> information and units:
>
> PROJ_INFO:
>
> 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
>
> PROJ_UNITS:
>
> unit: meter
> units: meters
> meters: 1
>
>   Using the wxPython GUI I import the source DEM specifying hdr.adf as 
> the
> ARC/GRID source. On the options tab I check "override projection 
> information
> and use location's projection" because that file has the units in feet:
>
> [rshepard at salmo /usr4/Oregon]$ less dem10-nw/prj.adf
> Projection    LAMBERT Datum         NAD83 Zunits        NO 
> Units         3.2808400000 Spheroid      GRS1980 Xshift        
> 0.0000000000 Yshift        0.0000000000 Parameters
>  43  0  0.000 /* 1st standard parallel
>  45 30  0.000 /* 2nd standard parallel -120 30  0.000 /* central meridian
>  41 45  0.000 /* latitude of projection's origin 400000.00000 /* false 
> easting (meters) 0.00000 /* false northing (meters)
>
>   However, after the file is imported and I run r.info on the map I see:
>
> Type of Map:  raster               Number of Categories: 5729 Data 
> Type:    CELL
> Rows:         18724
> Columns:      24657
> Total Cells:  461677668
> Projection: Lambert Conformal Conic
> N: 1735231.43724681    S: 1120657.1324816   Res: 32.82281055
> E: 952979.22944945    W: 143667.18968253   Res: 32.82281055
>
>   I cannot seem to be able to convert from feet to meters during the 
> import.
If I followed your post correctly, you should not be converting anything 
during the inport. You import into a Location defined with projection 
params exactly like the original ArcInfo file.
Then create a new, empty Location with units meters. Switch to the new 
location, import the region vector polygon (from v.in.region in the 
original Location), and set the region to that vector.
Now you should be ready to do r.proj to re-project the original (feet) 
raster to the new region with units=meters.

> The command used was:
>  r.in.gdal -o input="/usr4/Oregon/dem10-nw/hdr.adf" output="demNW10"
>
>   What have I missed here?
>
> Rich
>
>
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-- 
Micha Silver
Arava Development Co. +972-52-3665918
http://surfaces.co.il