SHGETNP - find the nearest points to a specified point in 3-space.

       To use SHGETNP, load the NCAR Graphics library ngmath.

       Copyright (C) 1997-2000
       University Corporation for Atmospheric Research

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

UNIX                                             September 1999                                  SHGETNP(3NCARG)

       PX          (real,input) The X coordinate value for a point P whose nearest neighbor is to be found.

       PY          (real,input) The Y coordinate value for a point P whose nearest neighbor is to be found.

       PZ          (real,input) The Z coordinate value for a point P whose nearest neighbor is to be found.

       X           (real, input) An array containing the X coordinates of the input data points.

       Y           (real, input) An array containing the Y coordinates of the input data points.

       Z           (real, input) An array containing the Z coordinates of the input data points.

       IFLAG       (integer,  input)  A  flag that equals 0 if this is the first call to this subroutine for the
                   given dataset and equals 1 otherwise.

       IRK         (integer, input) An integer workspace dimensioned for at least 2*N.

       RWK         (real, input) A real workspace dimensioned for at least 11*N+6.

       NP          (integer, output) An index such that (X(NP),Y(NP),Z(NP)) is the nearest input data  point  to
                   P. NP = 0 if IER .NE. 0. On successive calls to this subroutine after the first (that is when
                   IFLAG=1)  you  can  find  the  Mth closest point to (PX,PY,PZ) with the Mth call. IWK and RWK
                   should not be modified between calls to SHGETNP if you are wanting to find successive nearest
                   neighbors.

       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 shgrid_errors for details.

       SHGETNP - find the nearest points to a specified point in 3-space.

       shgrid, shseti, shgeti, shgrid_params.

       Complete documentation for Shgrid is available at URL
       http://ngwww.ucar.edu/ngdoc/ng/ngmath/shgrid/shhome.html

       CALL SHGETNP (PX, PY, PZ, N, X, Y, Z, IFLAG, IWK, RWK, NP, IER)

       SHGETNP is called to find the nearest point to a specified point in 3-space.  Successive calls to SHGETNP
       will  determine  the  point  nearest the specified point exclusive of the points found in previous calls,
       i.e. successive calls can be used to find the N nearest points for any N  between  one  and  the  maximum
       number of points in the input dataset.