[GRASS-user] problem displaying imported, rectified raster images
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.
how do the bounds and resolution compare with what r.info show?
"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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