#2100: r.proj bounding box too small by half a cell size (-g or -p):
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Reporter: awickert | Owner: grass-dev@…
Type: defect | Status: new
Priority: normal | Milestone: 7.0.0
Component: Default | Version: unspecified
Keywords: r.proj | Platform: Linux
Cpu: Unspecified |
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Comment(by awickert):
Replying to [comment:1 glynn]:
Thanks for the pointer towards bordwalk.c. Two thoughts:
(1) Reading the starting comments, it looks like this may in fact be
intentional to make sure that the region fits within the current region.
Indeed, when I tried to make changes to bordwalk.c, I found a reason to
believe that this was the case (below).
(2) However, this prevents the use of "-p" and "-g" to set the region of
the current location to match the region of the raster being projected.
This therefore means that the code as-is contradicts the help files, which
tell you to do this to ensure a good projection.
Therefore, I have attached a working diff that removes the parts that take
the bounding box a half-cell away from the cell margins... mostly. I have
not adjusted the for loops at all, which may need to be done for a real
fix, but was unnecessary for the test data set that I was using (48 cell
N-S x 96 cell E-W GCM outputs spanning the whole globe, so 90S to 90N and
180W to 180E). Also, I found that the output of the projection would
shrink to 2 cell widths (though still spanning the whole N-S range) if I
completely removed the western offset, so I just made that fairly small
for the time being; this may be a reason that the cell centers were used.
Anyway, this is only the second time I have done anything to the GRASS
source code, so I'd greatly appreciate what those of you more familiar
with this might have to say.
Cheers,
Andy Wickert
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Ticket URL: <https://trac.osgeo.org/grass/ticket/2100#comment:2>
GRASS GIS <http://grass.osgeo.org>