[GRASS-user] Creating mapset and/or importing data based on a proj4 string

[Helmut Kudrnovsky]

Ken Mankoff wrote
> Dear List,
> 
> Most of the time when I work with data in GRASS it is a provided on a
> standard GIS grid (EPSG code) and I can work with it easily. I create a
> location using the "-c" option when I start GRASS, or I import it into an
> existing mapset with r.import.
> 
> I'm now working with data and all I know is this:
> 
> +proj=stere +lat_0=90 +lat_ts=71 +lon_0=-39 +k=1 +x_0=0 +y_0=0
> +datum=WGS84
> +units=m +no_defs”
> 
> In the past, when working with a few variables and this information, and
> lat/lon grids in the NetCDF file, I would export the data (using Python)
> to
> lat,lon,data, and then r.in.ascii and project it that way. However, now
> I'm
> working with 14,000 high resolution daily records on the above projection.
> 
> It seems the only way to do this efficiently is to work in the projection
> of the data, and r.import the few other variables to this projection. Or
> perhaps cdo or gdal or some other 3rd party tool can quickly re-project
> everything for me to a known EPSG code. I've solved this before with
> vectors, ogr2ogr, and arbitrary proj4 strings.
> 
> Can anyone here suggest how to best get this data into GRASS?
> 
> I've tried using gdalwarp:
> 
> gdalwarp -of GTIFF -s_srs "+proj=stere +lat_0=90 +lat_ts=71 +lon_0=-39
> +k=1
> +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs" -t_srs EPSG:3413
> NETCDF:"${file}":RU out.tif
> 
> But am concerned because when I then run gdalinfo on the out.tif file, it
> reports strange bounds such as:
> 
> Origin = (-909.965548780931840,1546.900601999830769)
> Pixel Size = (7.477558376763198,-7.477558376763198)
> Corner Coordinates:
> Upper Left  (    -909.966,    1546.901) (165d27'58.34"E, 89d59' 0.36"N)
> Lower Left  (    -909.966,   -1264.661) ( 80d44'10.54"W, 89d59' 8.22"N)
> Upper Right (     794.918,    1546.901) (107d48' 8.56"E, 89d59' 2.20"N)
> Lower Right (     794.918,   -1264.661) ( 12d50'53.17"W, 89d59'10.36"N)
> Center      (     -57.524,     141.120) (157d10'37.34"E, 89d59'54.94"N)
> 
> Which seems to be very close to the pole (both lower and upper at >89
> deg).
> This should be covering a much large portion of the Arctic.

e.g. you can use a proj4 string in the startup wizard to create a new
location.

just tested with your proj4 string,

g.proj -j                                                                       
+proj=stere
+lat_0=90
+lat_ts=71
+lon_0=-39
+k=1
+x_0=0
+y_0=0
+no_defs
+a=6378137
+rf=298.257223563
+towgs84=0.000,0.000,0.000
+to_meter=1

HTH



-----
best regards
Helmut
--
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