Interpolation: grid --> observation point

[Andy Loughe <loughe(at)fsl.noaa.gov>]

Hello,

I have inherited code that takes atmospheric model (gridded) data 
and interpolates it to station observation points that report 
hourly precipiation.  The model points form a cartesian coordinate 
system, while the station observations are spread randomly
within the boundaries of the full model domain.

Currently, a bi-linear approach is used to interpolate the 
model data to each observation point.  This method uses the 
four closest model grid points which surround the observation 
point.

I would like to use more than just the four model grid points
which surround the observation point, and weight the more distant
points appropriately.

Any suggestions on effective methods for doing this in IDL?

Thanks!

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Andrew F. Loughe    email:loughe@fsl.noaa.gov    phone:(303)497-6211