Ubuntu Manpage: PPDIPO - generates and returns the boundary of the "difference" polygon, which consists of

NAME

       PPDIPO - generates and returns the boundary of the "difference" polygon, which consists of
       all points that are inside the subject polygon but not inside the clip polygon.

SYNOPSIS

       CALL PPDIPO (XCCP,YCCP,NCCP,XCSP,YCSP,NCSP,RWRK,IWRK,NWRK,URPP,IERR)

C-BINDING SYNOPSIS

       #include <ncarg/ncargC.h>

       void c_ppdipo(
            float *xccp,
            float *yccp,
            int nccp,
            float *xcsp,
            float *ycsp,
            int ncsp,
            float *rwrk,
            int *iwrk,
            int nwrk,
            int (*urpp_)( float *xcra, float *ycra, int *ncra),
            int *ierr)

DESCRIPTION

XCCP (an input array of type REAL) is the X coordinate array for the clip polygon.

YCCP (an input array of type REAL) is the Y coordinate array for the clip polygon.

NCCP (an input expression of type INTEGER) is the number of points defining the
clip polygon.

XCSP (an input array of type REAL) is the X coordinate array for the subject
polygon.

YCSP (an input array of type REAL) is the Y coordinate array for the subject
polygon.

NCSP (an input expression of type INTEGER) is the number of points defining the
subject polygon.

RWRK (a scratch array, dimensioned NWRK, of type REAL) is a real workspace array.
Because of the way in which they are used, RWRK and IWRK may be EQUIVALENCEd
(and, to save space, they should be).

IWRK (a scratch array, dimensioned NWRK, of type INTEGER) is an integer workspace
array. Because of the way in which they are used, RWRK and IWRK may be
EQUIVALENCEd (and, to save space, they should be).

NWRK (an input expression of type INTEGER) is the length of the workspace array(s).
It is a bit difficult to describe how much space might be required. At the
moment, I would recommend using NWRK equal to about ten times the total of the
number of points in the input polygons and the number of intersection points.
This situation will change with time; at the very least, I would like to put
in an internal parameter that will tell one how much space was actually used
on a given call, but I have not yet done so.

URPP is the name of a user-provided routine to process the polygon-boundary pieces.
This name must appear in an EXTERNAL statement in the routine that calls
PPDIPO and the routine itself must have the following form:

SUBROUTINE URPP (XCRA,YCRA,NCRA)
DIMENSION XCRA(NCRA),YCRA(NCRA)
...(code to process a polygon boundary piece)...
RETURN
END

Each of the arguments XCRA and YCRA is a real array, dimensioned NCRA; the
former holds the X coordinates, and the latter the Y coordinates, of a piece
of the polygon boundary. It will be the case that XCRA(NCRA)=XCRA(1) and
YCRA(NCRA)=YCRA(1).

IERR (an output variable of type INTEGER) is returned with the value zero if no
errors occurred in the execution of PPDIPO or with a small positive value if
an error did occur. The value 1 indicates that a degenerate clip polygon was
detected, the value 2 that a degenerate subject polygon was detected, and the
value 3 that the workspace provided was too small; values greater than 3
should be reported to the author, as they indicate some problem with the
algorithm. Currently, if IERR is returned non-zero, one can be sure that no
calls to URPP were executed; in the future, this could change, but, in that
case, there will be an internal parameter allowing one to request the current
behavior.

C-BINDING DESCRIPTION

       The C-binding argument descriptions are the same as the FORTRAN argument descriptions.

USAGE

       The FORTRAN statement

       CALL PPDIPO (XCCP,YCCP,NCCP,XCSP,YCSP,NCSP,RWRK,IWRK,NWRK,URPP,IERR)

       causes the formation of a difference polygon (the subject polygon minus the clip polygon)
       and the delivery of that polygon's boundary, piece by piece, to the user-specified
       polygon-processing routine URPP.

EXAMPLES

       Use the ncargex command to see the following relevant examples: ppex01, tppack, c_ppex01.

ACCESS

       To use PPDIPO or c_ppdipo, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c,
       preferably in that order.

COPYRIGHT

       Copyright (C) 1987-2009
       University Corporation for Atmospheric Research
       The use of this Software is governed by a License Agreement.