[GRASS-user] r.proj manual clarification

[Rich Shepard]

   In the Notes section of the 7.5 r.proj manual the second and third
paragraphs read,

"To avoid excessive time consumption when reprojecting a map the region and
resolution of the target location should be set appropriately beforehand."

   Isn't the target's location and region set when that location is created?
What happens to other maps (vector and raster) in that location if the
region and resolution are changed to match that of the source map? I thought
that r.proj was the tool to convert the source's region and resolution to
that of the target.

"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."

   The first sentence checks the source (current) location's projection. The
third sentence suggests snapping the source grid's region and resolution to
a regular grid. Two questions about this: 1) aren't all raster maps on a
regular grid? and 2) how does this change affect the source location?

   I'm working on understanding how to correct r.proj failures because the
source map/location is outside the bounds of the target location.

TIA,

Rich