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.

UNIX                                                May 2000                                  c_cssgridd(3NCARG)