bilinear/cubic convolution

[Chris W Skelly]

Darrell,

> Hello all. I would like to use bilinear interpolation or cubic
> convolution interpolation to do some cross validation when
> interpolating site data to raster format. My site data are scattered
> and their locations will not necessarily line up with cell centers.
> I'm trying to do a little better than just picking the nearest cell to
> estimate an error.
> 
> My question is: is this capability already available in GRASS?

I am not sure if I understand you, but if you are going from site
to cell and you use something like idw or krig the absolute distance
from the site position to the cell center is used in the
interpolation. The actual point ceases to exist at the end of the
day so whether it lines up with a cell centre or not is irrelavent.
If you want exact interpolation (ie you want that specific
point value to exist in the cell layer) they you just weight it
appropriately.

Can you explain why scattered data is a problem, I think I am 
missing something...

chris