I've run into an odd issue that could be a problem for anyone needing precise calculations from a landsat (or possibly other) image.
I have a landsat ETM image with a resolution of 28.5m for the bands 1-5, 7 and resolution of of 14.25m for band 8. If I set the region to exactly match one of the landsat channels (g.region rast=landsat_band8, for example) and copy the image with r.mapcalc (r.mapcalc expression='new_band8=landsat_band8'), GRASS produces an exact copy. However, if I set the region in other ways (e.g., via g.region setting the bounds, interactively in the GUI) any copy of the image made with r.mapcalc is shifted by half a cell. This happens whether or not I set the -a (align) flag. This does not seem to be a problem for another landsat with a 15m resolution (that is, not a fraction of a meter). Has anyone else run into this? Any ideas? I'm working with GRASS 7 compiled a couple days ago. Michael On Jun 8, 2012, at 1:26 AM, Markus Neteler wrote: > This is definitely for grass-dev. Perhaps an issue in the Python interface? > But it would be important to know what " if I set the region any other way" > exactly means. > > Markus > > On Fri, Jun 8, 2012 at 6:54 AM, Michael Barton <[email protected]> wrote: >> In trying to figure out why I was getting some odd results in the sharpening >> algorithms, I discovered a weird problem. >> >> I've zoomed in on a landsat to run the pan sharpening routines faster (to >> test various changes in the code) and see in better detail the results. When >> I make a copy of the panchromatic map, I find that the copy is shifted by >> 1/2 cell from the original. If I set region to exactly match all of the pan >> map (g.region rast=pan), there is no shift. But if I set the region any >> other way, there is a 1/2 cell shift. This means that every map I make will >> not align with my original landsats. This causes problems in the sharpening >> algorithms in different places. The worst seems to be in the PCA >> sharpening. I've quit GRASS and restarted and this shift is still there. It >> doesn't seem to matter whether I use the -a flag or not in g.region. >> >> Is this a known issue? Is there some way around it? >> >> Michael >> _____________________ >> C. Michael Barton >> Visiting Scientist, Integrated Science Program >> National Center for Atmospheric Research & >> University Consortium for Atmospheric Research >> 303-497-2889 (voice) >> >> Director, Center for Social Dynamics & Complexity >> Professor of Anthropology, School of Human Evolution & Social Change >> Arizona State University >> www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu >> >> >> >> >> _____________________ C. Michael Barton Visiting Scientist, Integrated Science Program National Center for Atmospheric Research & University Corporation for Atmospheric Research 303-497-2889 (voice) Director, Center for Social Dynamics & Complexity Professor of Anthropology, School of Human Evolution & Social Change Arizona State University www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu _______________________________________________ grass-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-dev
