Thanks very much. This is a definite help. I somehow missed the align argument in g.region. So, whatever reason for this shift, this seems to be a very good way around it. Works great!
Michael On Jun 8, 2012, at 1:00 PM, <[email protected]> <[email protected]> wrote: > From: Markus Metz <[email protected]> > Date: June 8, 2012 12:53:57 PM MDT > To: Michael Barton <[email protected]> > Cc: <[email protected]> > Subject: Re: [GRASS-dev] shifting maps created with r.mapcalc > > > On Fri, Jun 8, 2012 at 8:26 PM, Michael Barton <[email protected]> wrote: >> 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. > > Since r.mapcalc operates on the current region, and r.mapcalc produces > a correct result with g.region rast=landsat_band8, I would recommend > not to use the -a flag, but use g.region align=landsat_band8 after > setting the region in other ways. The GUI can not make use of the > align option itself because it does not know how the previous region > has been set. > > HTH, > > Markus M > >> >> 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 > _____________________ 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
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