NAME

       SURF2 - 2D interpolation for gridded data

SYNOPSIS

       FUNCTION SURF2 (XX, YY, M, N, X, Y, Z, IZ, ZP, SIGMA)

       This  function  interpolates  a  surface  value at a specified coordinate using bi-splines
       under tension. SURF1 must be called before invoking SURF2. The desired interpolated  value
       is returned as the value of the function.

DESCRIPTION

       XX          (real,  input)  Contains  the  X  coordinate  of a point to be mapped onto the
                   interpolated surface.

       YY          (real, input) Contains the Y coordinate of a  point  to  be  mapped  onto  the
                   interpolated surface.

       M           (integer, input) The number of grid lines in the X direction. (M > 1)

       N           (integer, input) The number of grid lines in the Y direction. (N > 1)

       X           (real,  input)  An  array  containing  M X coordinates for grid lines in the X
                   direction. These values must be strictly increasing.

       Y           (real, input) An array containing N Y coordinates for  grid  lines  in  the  Y
                   direction. These values must be strictly increasing.

       Z           (real,  input) An array containing M x N functional values at the grid points;
                   Z(I,J) contains the functional value at (X(I),Y(J)) for I=1,M and J=1,N.

       IZ          (integer, input) The row dimension of the matrix Z  (IZ  is  greater  than  or
                   equal to M).

       ZP          (real, input) An array of size M x N x 3.

       SIGMA       (real, input) Tension factor. Values near zero result in a cubic spline; large
                   values (e.g. 50) result in nearly a polygonal line. A typical value is 1.

RETURN VALUE

       SURF2 returns the interpolated value at the specified point T.

ACCESS

       To use SURF2, load the NCAR Graphics library ngmath.

SEE ALSO

       surf1, fitgrid_params.

       Complete documentation for Fitgrid is available at URL
       http://ngwww.ucar.edu/ngdoc/ng/ngmath/fitgrid/fithome.html

COPYRIGHT

       Copyright (C) 2000
       University Corporation for Atmospheric Research

       The use of this Software is governed by a License Agreement.