s.datum.shift:
datum shift module working on files (like m.datum.shift).
Mainly needed for testing purposes of datum shift functions
from CC library.
Mainly modeled after s.proj of Bill Brown. 

input= input sites list
output= output sites list
idatum= map datum of input file
[odatum=] map datum of output file, read from PROJ_INFO if not set

-m use molodensky formula, faster than block shift, but less precise

not implemented:
-w bursa-wolf/helmert transformation


long term development:
include this functionality to s.proj.
add same functionality to v.proj and r.proj. 

add datum shift functions from PROJ4.4.2 to GRASS
and make them available transparently within GRASS.


general considerations:

GRASS can be used from global to microscopic scale,
there is no way of knowing the acutal scale from the programmers
standpoint, so that the user can not be guided to choose 
the appropriate function/model.

E. g. on a global database in lat/lon datum shifts make no sense.
If you are in a database with nation-wide extension in the scale of 
1:1.000.000 you do not need any datum transformation.
Or if you have an archeological site with an extent in the range of some 
tens of meters the block shift and molodensky transformation will give
no reasonable results, as the error is in the range of 5 to 15 meters.

So be careful and think about the precision you really need. 
-- 
10/2000
andreas.lange@rhein-main.de