NAME

       c_cssgridd - tension spline interpolation on a sphere

FUNCTION PROTOTYPE

       double *c_cssgridd(int, double [], double [], double [],
                        int, int, double [], double [], int *);

SYNOPSIS

       double *c_cssgridd (n, rlat, rlon, f, ni, nj, plat, plon, ier)

DESCRIPTION

       n           The number of input data points, n > 2.

       rlat        An  array  containing  the  latitudes of the input data, expressed in degrees.
                   The first three points must not be collinear (lie on a common great circle).

       rlon        An array containing the longitudes of the input data, expressed in degrees.

       f           Array  containing   data   values.   f[i]   is   the   functional   value   at
                   (rlat[i],rlon[i]) for i = 0 to n-1.

       ni          The number of latitudes in the interpolated grid.

       nj          The  number  of longitudes in the interpolated grid.  ni and nj can both be 1,
                   allowing for interpolation at a single point.

       plat        An array containing the latitudes of the points where interpolated values  are
                   to be computed.  The values in plat should be in degrees.

       plon        An  array  of  length nj containing the longitudes the output grid lines.  The
                   values in plon should be in degrees.

       ier         An error return value. If *ier is returned as 0, then no errors were detected.
                   If  *ier  is  non-zero,  then  refer  to  the error list in cssgrid_errors for
                   details.

USAGE

       c_cssgridd is called to find an interpolating tension spline for randomly positioned  data
       on a unit sphere. c_cssgridd is a double precision version of c_cssgrid.

RETURN VALUE

       c_cssgridd  returns  a pointer to a linear array of data that contains interpolated values
       at user-specified lat/lon pairs. The returned array stores its values as if  they  were  a
       2-dimensional  C  array  with  latitude being the first dimension and longitude the second
       dimension. That is, if out is declared as

         double *out;

       and we set:

         out = c_cssgridd(n, rlat, rlon, f, nlat, nlon, plat, plon, &ier);

       then out[i*nlon+j] is the  interpolated  function  value  at  coordinate  point  (plat[i],
       plon[j])  for  0 <= i < nlat and 0 <= j < nlon. The space for out is allocated internal to
       c_cssgridd and is nlat * nlon doubles in size.

ACCESS

       To use c_cssgridd, load the NCAR Graphics library ngmath.

SEE ALSO

       c_cssgrid, css_overview, cssgrid_errors

       Complete documentation for Cssgrid is available at URL
       http://ngwww.ucar.edu/ngdoc/ng/ngmath/cssgrid/csshome.html

COPYRIGHT

       Copyright (C) 2000
       University Corporation for Atmospheric Research

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