[GRASS-user] Once more: raster projection transformation: LAEA -> UTM

[Maciej Sieczka]

Jana K. pisze:
> I've already posted this a couple of days ago, but I am afraid
> somehow it got lost in other questions. I believe someone must know
> an answer, so please, HELP me :-(:
> 
> I need to transform a map from LAEA coordinates into UTM. I created a
> new location with UTM projection. I used r.proj from within the new
> location, but  running it,  I received the following error message:
> 
> Input Projection Parameters: +proj=laea +lat_0=52.0000000000 
> +lon_0=10.0000000000 +x_0=4321000.0000000000 +y_0=3210000.0000000000 
> +a=6378137 +rf=298.257222101 +no_defs +towgs84=0.000,0.000,0.000 
> Input Unit Factor: 1
> 
> Output Projection Parameters: +proj=utm +zone=34 +a=6378137 
> +rf=298.257223563 +no_defs +towgs84=0.000,0.000,0.000 Output Unit
> Factor: 1
> 
> Can't work with xy data
> 
> I don't understand it as the data are clearly georeferenced.

Looks like you do have correct settings in the PROJ_INFO in both
PERMANENT mapsets. Can you post the header file of the raster map you
want to reproject? Maybe it's malformed, for whatever reason. You'll
find it in location/mapset/cellhd folder.

> Do I need to make a transformation to lat/lon beforehand?

In general avoid reprojecting rasters more often than needed - each
reprojection introduces some distortion to data.

> Now question 2:
> 
> My raster data are categorical (landuse), and during the projection 
> transformation I want to go from high resolution (100m) to rather
> crude resolution (2500m). How GRASS handles such operation? I would
> expect that It assigns the highest frequency value to the new cell (I
> mean if one new cell contains 625 old pixels, it will be assigned the
> value which occurs most frequently). Am I right?

Look into section 'Design of r.proj' in the r.proj manual. In 'NOTES'
you'll find instructions on how to maintain input and output region
settings.

Best,
Maciek

-- 
Maciej Sieczka
www.sieczka.org