[GRASSLIST:4432] Re: bug fixes for tcltkgrass for GRASS 5.3

Hamish hamish_nospam at yahoo.com
Thu Sep 30 00:50:48 EDT 2004

> > > BTW - what is the r.surf.idw2 for anyway when it is slower, less
> > > universal and gives identical results. Strange... Ask Grass developers?
> >
> > I don't know what the difference is either.
> Can anybody say if there are any more diffrences between the r.surf.idw2
> and *idw which justify both them being available?

from the 5.3 r.surf.idw help page:

Unlike r.surf.idw2, which processes  all  input  data  points  in  each
interpolation  cycle,  r.surf.idw  attempts  to  minimize the number of
input data for which distances must be calculated.  Execution speed  is
therefore a function of the search effort, and does not increase appre-
ciably with the number of input data points.

r.surf.idw will generally outperform r.surf.idw2 except when the  input
data layer contains few non-zero data, i.e. when the cost of the search
exceeds the cost of the additional distance calculations  performed  by
r.surf.idw2.   The  relative performance of these utilities will depend
on the comparative speed of boolean, integer and floating point  opera-
tions on a particular platform.


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