# ncl_ppunpo man page

PPUNPO — generates and returns the boundary of the "union" polygon, which consists of all points that are inside either or both of the clip polygon and the subject polygon.

## Synopsis

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

## C-Binding Synopsis

#include <ncarg/ncargC.h>

```
void c_ppunpo(
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 PPUNPO 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 PPUNPO 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 PPUNPO (XCCP,YCCP,NCCP,XCSP,YCSP,NCSP,RWRK,IWRK,NWRK,URPP,IERR)`

causes the formation of a union polygon (of the subject and clip polygons) 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 PPUNPO or c_ppunpo, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in that order.

## See Also

Online: polypack, ppdipo, ppditr, ppinpo, ppintr, ppplcl, ppppap, ppuntr, ncarg_cbind.

Hardcopy: None.

## Copyright

Copyright (C) 1987-2009

University Corporation for Atmospheric Research

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