s.surf.idw

[Michael Shapiro]

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.

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|	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
|
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|



Michael