[GRASSLIST:4604] Re: map reprojections and datum support.

[Glynn Clements]

giorgio wrote:

> Is there a method in GRASS to reproject a raster  map from a datum to another 
> performing more and different operations then (r.proj) and eventually 
> utilizing other free software (f.e. proj geotrans etc.) ?.

The only method which GRASS provides directly is r.proj, and that
doesn't currently handle datum conversions other than NAD27<->NAD83. 
Hopefully, arbitrary datum conversions will be supported in future
versions (GRASS already has datum conversion code, but it isn't used
by the *.proj programs).

If you wish to use other software, you can convert the raster to a
sites file with r.to.sites, then export the sites file with
s.out.ascii. The resulting output will be in a format which is
amenable to further processing using awk, perl etc, and should be
directly usable by proj and cs2cs.

The processed data can be re-imported with s.in.ascii. Converting the
sites file to a raster is more complex, as the sites will no longer
form a rectangular grid. Available options include s.to.rast (which
may leave gaps) and s.surf.rst (which only works for data for which
interpolation is meaningful, e.g. elevations, not for discrete
categories).

-- 
Glynn Clements <glynn.clements at virgin.net>