4D interpolation

[Eric S Fraga]

I've been following the brief thread on interpolation with interest.
Very helpful.

However, I have a problem in which I need to interpolate (2d only)
onto a surface that is not square.  Given interp2:

     ZI = interp2 (X, Y, Z, XI, YI)

I wish to interpolate (or maybe, if need be, approximate) Z to get ZI
where XI and YI are not the same size.  And neither are the original X
and Y for that matter.  interp2 does not allow this.  Can anybody
please suggest an alternative?

Thanks,
eric