ZI = GRIDDATA(X,Y,Z,XI,YI) returns matrix ZI containing elements
corresponding to the elements of matrices XI and YI and determined by
interpolation within the 2-D function described by the (usually)
nonuniformly-spaced vectors (X,Y,Z).
XI can be a row vector, in which case it specifies a matrix with
constant columns. Similarly, YI can be a column vector and it
specifies a matrix with constant rows.
[XI,YI,ZI] = GRIDDATA(X,Y,Z,XI,YI) returns the XI and YI formed
this way, which are the same as the matrices returned by MESHGRID .
GRIDDATA uses an inverse distance method.
See also INTERP2 , INTERP1 .