[GRASS-user] Re: correcting a series of images for wrong bounding
micha at arava.co.il
Fri May 1 14:54:49 EDT 2009
> Micha wrote:
>> So r.region actually does a kind of affine transformation? I don't
>> remember seeing this documented anywhere (the manual says
>> "...manage the boundaries...") , and I must say it's confusing and
>> unexpected that a module called r.region (similar to g.region)
>> shifts/changes the data, rather than just defining the region
>> and resolution.
> it does not touch the data array. It only modifies where that array is
> thought to be in space. i.e. it just edits the $MAPSET/cellhd/$MAPNAME
> if you put new bounds which don't exactly match the array size it will
> adjust your resolution so that it does.
I guess my misunderstanding is just semantic. If the module were named
r.shift or r.translate I'd have no problem.
If I do something silly like: starting with a raster with an extent of
N=560000 and S=360000 and I run:
r.region map n=480000 s= 440000
then the raster gets "squashed" into the smaller region.
By comparison, there's no v.region which shifts where the vector
features are in space. But if I choose to shift a vector map, I use the
"move" tool in v.edit. That makes perfect sense, but r.region doing such
a shift caught me by surprise. So r.region seems closer to gdalwarp
that to any region settings.
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