Rich Shepard wrote
> On Tue, 20 Sep 2016, Helmut Kudrnovsky wrote:
>> If it is about raster reprojection, there are hints in the r.proj manual
>> about region settings before applying r.proj.
>> A simple way to do this is to check the projected bounds of the input map
>> in the current location's projection using the -p flag. The -g flag
>> reports the same thing, but in a form which can be directly cut and
>> pasted
>> into a g.region command. After setting the region in that way you might
>> check the cell resolution with "g.region -p" then snap it to a regular
>> grid with g.region's -a flag. E.g. g.region -a res=5 -p. Note that this
>> is
>> just a rough guide.
>> A more involved, but more accurate, way to do this is to generate a
>> vector
>> "box" map of the region in the source location using -d. This
>> "box" map is then reprojected into the target location with v.proj. Next
>> the region in the target location is set to the extent of the new vector
>> map with g.region along with the desired raster resolution (g.region -m
>> can be used in Latitude/Longitude locations to measure the geodetic
>> length
>> of a pixel). r.proj is then run for the raster map the user wants to
>> reproject. In this case a little preparation goes a long way.
> Helmut,
>    Thank you very much. This expansion of Micha's explanation is really
> valuable and I greatly appreciate it. I wasn't aware of this need and
> process the last time (years ago) I had a need to reproject data. Source
> data in recent projects were all in the same projection and appropriate to
> the area studied.
> Regards,
> Rich
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> grass-user@.osgeo


It's copy /paste from the manual. So the manual is your best friend. ;-) 

best regards
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