[GRASS-user] A question about raster map resolutions

[Rich Shepard]

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 v.in.region -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