[GRASS-dev] v.surf.idw: a improvement

[E. Jorge Tizado]

Hi 

A few lines permit add a new type of interpolation in v.surf.idw, the 
exponential interpolation similar to "Geographically Weighted Regression":

weigth = exp( - distance^2 / bandwidth^2)

I attach the diff files, the core is

for (n = 0; n < nsearch; n++)
{
	d = exp( - list[n].dist / bw );
	sum1 += list[n].z * d;
	sum2 += d;
}

P.S. idw = interpolation distance weight, better than inverse distance weight
to future more type of interpolations

-- 
E. Jorge Tizado
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