[GRASS-dev] [GRASS GIS] #2757: r.import: ERROR: Input raster map is outside current region

[Moritz Lennert]

On 13/10/15 15:58, Markus Neteler wrote:
> On Tue, Oct 13, 2015 at 3:37 PM, Anna Petrášová <kratochanna at gmail.com> wrote:
>> On Tue, Oct 13, 2015 at 9:03 AM, Markus Neteler <neteler at osgeo.org> wrote:
>>
>> It is sort of hidden in the Optional tab, I am not sure if we gain much by
>> hiding it completely.
>
> As mentioned, I don't even understand the meaning of -n in r.proj. If
> anyone knows, please rephrase it in r.proj's manual.

In r.proj, -n provokes a call to bordwalk(), which is described in the 
code (bordwalk.c) as doing the following:

  * bordwalk.c - projects the border cell centers of a map or region
  * to check whether they are inside the borders of another map/region
  * in a different location, and adjusts the cell header so
  * only overlapping areas are included. The function is called by main,
  * first to project the output region into the input map and trim the
  * borders of this in order to get a smaller map, and faster and less 
hungry
  * memory allocation. Then main calls the function again, but reversed,
  * to project the input map on the output region, trimming this down to
  * the smallest possible rectangular region.

So, IIUC, this means that -n already crops the input map in the input 
location before reprojection, instead of only writing those parts of the 
output map that fall into the current region. This makes reprojection 
faster if the target region is only a subset of the input map (again AFAIU).

Moritz