[GRASS-user] problem displaying imported, rectified raster images

Hamish hamish_nospam at yahoo.com
Wed May 9 01:11:31 EDT 2007

pete davidson wrote:
> For several days I assumed I was making a mistake somewhere in the
> r.in.gdal/ i.target / i.points / i.rectify process.  However, this
> morning I opened qgis to do something else, then on a whim created a
> new map, displayed a couple of pre-existing vector layers from the
> grass 'real_location' location, then added the grass raster layer
> TL0232.blue_1.  To my surprise it displayed perfectly.  Correctly
> oriented and rectified and in a usable resolution and everything.
> Back in grass, if I do
> - g.region rast=TL0232.blue_1
> - d.mon x0
> - d.rast TL0232.blue_1
> I get a correctly displayed raster,

ok, so your rectification process should be ok.

use r.info anytime and r.univar after "g.region rast=" to get an idea
about what data is actually in your map. (rows, columns, resolution)

> however as soon as I do g.region -d to go back to the (larger) default
> region, any attempt to display the raster again produces an unusably
> low-res version..

The default region or default region resolution is wrong? d.rast works
in the current region, not the map's region. It resamples the raster map
on the fly.

 g.region -d
 g.region -p

how do the bounds and resolution compare with what r.info show?
(same as)
 g.region rast=TL0232.blue_1
 g.region -p

"g.region -d" will always use what you specified when you first created
the location. (stored in $MAPSET/PERMANENT/DEFAULT_WIND)

I expect the default resolution was set to something much coarser than
your rectified map's resolution, and it is simply a mis-display.


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