NATGRIDD - primary double precision Fortran entry for natural neighbor gridding

       To use NATGRIDD, load the NCAR Graphics library ngmath.

       Copyright (C) 2000
       University Corporation for Atmospheric Research

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

UNIX                                             March 1997-1998                                NATGRIDD(3NCARG)

       NPNTS       (Integer, Input) - The number of input data points. (NPNTS > 3).

       X           (Double precision, Input) - An array containing the X coordinates of the input data points.

       Y           (Double precision, Input) - An array containing the Y coordinates of the input data points.

       Z           (Double  precision,  Input)  -  An  array  containing the functional values of the input data
                   points. That is, Z(L) is the value of the  input  function  at  coordinate  (X(L),Y(L)),  for
                   L=1,NPNTS.

       NUMXOUT     (Integer, Input) - The number of X values in the output grid.

       NUMYOUT     (Integer, Input) - The number of Y values in the output grid.

       XI          (Double precision, Input) - An array of dimension NUMXOUT containing the X coordinates of the
                   output data grid. The values in XI must be increasing, but need not be equally spaced.

       YI          (Double precision, Input) - An array of dimension NUMYOUT containing the Y coordinates of the
                   output data grid. The values in YI must be increasing, but need not be equally spaced.

       ZI          (Double  precision,  Output)  -   A  two-dimensional  array  of  dimension  NUMXOUT x NUMYOUT
                   containing the interpolated functional values. ZI(I,J) is  the  interpolated  value  at  grid
                   point (XI(I),YI(J)).

       IER         (Integer,  Output)  -  An  error  return  value. If IER is returned as 0, then no errors were
                   detected. If IER is non-zero, then refer to the man page for natgrid_errors for details.

       NATGRIDD - primary double precision Fortran entry for natural neighbor gridding

       natgrid, natgrid_params, nnseti, nngeti, nnsetrd, nngetrd, nnsetc, nngetc.

       Complete documentation for Natgrid is available at URL
       http://ngwww.ucar.edu/ngdoc/ng/ngmath/natgrid/nnhome.html

       CALL NATGRIDD (NPNTS, X, Y, Z, NUMXOUT, NUMYOUT, XI, YI, ZI, IER)

       NATGRIDD is the double precision gridding function in the Natgrid package.  The behavior of  NATGRIDD  is
       controlled  by  values  set  for  the  various  parameters described in natgrid_params.  Values for these
       parameters can be set using the subroutines NNSETI, NNSETRD, and NNSETC.