[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.
Hamish
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