NNPNTD - Interpolate at a single point in double precision

       To use NNPNTD, 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                                  NNPNTD(3NCARG)

       X           (Double precision, Input) - The X coordinate of the point where interpolation is desired.

       Y           (Double precision, Input) - The Y coordinate of the point where interpolation is desired.

       Z           (Double precision, Output) - The interpolated functional value at the point (X,Y).

       NNPNTD - Interpolate at a single point in double precision

       natgrid, natgrid_params, natgridd, nnpntinitd, nnpntendd.

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

       CALL NNPNTD (X, Y, Z)

       This  subroutine is called when you want to interpolate at an individal point.  NNPNTINITD must be called
       prior to calling NNPNTD and NNPNTENDD must be called to terminate single point mode.