[GRASS-dev] shifting maps created with r.mapcalc

[Michael Barton]

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, <grass-dev-request at lists.osgeo.org>
 <grass-dev-request at lists.osgeo.org> wrote:

> From: Markus Metz <markus.metz.giswork at googlemail.com>
> Date: June 8, 2012 12:53:57 PM MDT
> To: Michael Barton <michael.barton at asu.edu>
> Cc: <grass-dev at lists.osgeo.org>
> Subject: Re: [GRASS-dev] shifting maps created with r.mapcalc
> 
> 
> On Fri, Jun 8, 2012 at 8:26 PM, Michael Barton <michael.barton at asu.edu> 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 <michael.barton at asu.edu> 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
>> grass-dev at lists.osgeo.org
>> 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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/grass-dev/attachments/20120608/19bb2e67/attachment.html>