[GRASS-user] r.proj manual clarification

[Helmut Kudrnovsky]

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

gdalwarp - Warp an image into a new coordinate system
(http://www.gdal.org/gdalwarp.html)

try gdalwarp to see how the raster is re-projected there and then compare
the settings in GRASS.

>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?

the real strength of GRASS in raster is, that you can change the computional
region of interest to extent and resolution to what fits best for your
analysis. you can change back to resolution and extend to your original
data.

https://grass.osgeo.org/grass75/manuals/g.region.html tells:

" The user can create, modify, and store as many geographic region
definitions as desired for any given mapset. "

https://grass.osgeo.org/grass75/manuals/rasterintro.html tells:

"GRASS raster map processing is always performed in the current region
settings (see g.region), i.e. the current region extent and current raster
resolution is used. If the resolution differs from that of the input raster
map(s), on-the-fly resampling is performed (nearest neighbor resampling). If
this is not desired, the input map(s) has/have to be resampled beforehand
with one of the dedicated modules.

The built-in nearest-neighbour resampling of raster data calculates the
centre of each region cell, and takes the value of the raster cell in which
that point falls.

If the point falls exactly upon a grid line, the exact result will be
determined by the direction of any rounding error. One consequence of this
is that downsampling by a factor which is an even integer will always sample
exactly on the boundary between cells, meaning that the result is
ill-defined. "

what is missing in the manuals?







-----
best regards
Helmut
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