s.surf.idw

[Bob Harrington]

>idw stands for "inverse distance weighting" which means that  for
>a  given  location  to  be interpolated, N known points "near" to
>this point are selected and the z values for  the  N  points  are
>averaged  to  form  a z value for this location. The "average" is
>weighted - points farther away are given less weight than  points
>nearby.  The  value  for  N  is  chosen  by  the user. The points
>selected  are  the  N  points  nearest   the   location   to   be
>interpolated.   The  distance  measure  is  Euclidean for UTM and
>other  planimetric  grids,   geodesic   distance   for   lat-lon.
>r.surf.idw  and  s.surf.idw  differ only in that the known points
>are posted to the center of gird cells in r.surf.idw  whereas  in
>s.surf.idw the know points are not so constrained.

>|
>|
>|	I would like some information on the method used to
>|generate the surface with s.surf.idw. What method was used? Is
>|it similar to the "moving average" technique (Geo.
>|Stats.--J.C.Davis)? Does it use the Pythagorean equation? Are
>|s.surf.idw methods similar to the methods used in r.surf.idw?
>|What would be a good reference for s.surf.idw?
>|
>|
>|Regards,
>|
>|
>|Bruce Wylie
>|
>|
>|



>Michael

While on this subject: what is a good source of kriging programs for
use with GRASS? I would like to do cokriging on data that I have in
grass site maps to produce a raster map. 

Cheers,

Bob Harrington
Hydrology and Water Resources
University of Arizona