# ncl_polypack - Man Page

a set of routines allowing polygons to be manipulated in various ways. Each of the six principal routines is given a "clip" polygon, a "subject" polygon, and a workspace; it operates on the two polygons in some way to create either a derivative polygon or a set of trapezoids representing the interior of that derivative polygon and then passes these on to a user-specified processing routine.

## Synopsis

`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.`

`PPINPO - generates and returns the boundary of the "intersection" polygon, which consists of all points that are inside both the clip polygon and the subject polygon.`

`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.`

`PPDITR - generates and returns a set of trapezoids representing the interior of the "difference" polygon, which consists of all points that are inside the subject polygon but not inside the clip polygon.`

`PPINTR - generates and returns a set of trapezoids representing the interior of the "intersection" polygon, which consists of all points that are inside both the clip polygon and the subject polygon.`

`PPUNTR - generates and returns a set of trapezoids representing the interior of the "union" polygon, which consists of all points that are inside either or both of the clip polygon and the subject polygon.`

`PPPPAP - can be called to preprocess a polygon in such a way as to remove certain peculiarities that can cause minor cosmetic errors in the output from the routines that return trapezoids.`

`PPPLCL - clips a polyline against a clipping rectangle. It is intended that, eventually, there should be a better routine that will clip a polyline against an arbitrary polygon, but that routine has not yet been written.`

## C-Binding Synopsis

#include <ncarg/ncargC.h>

c_ppdipo

c_ppditr

c_ppinpo

c_ppintr

c_ppplcl

c_ppppap

c_ppunpo

c_ppuntr

## Access

To use Polypack routines, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in that order.

## Messages

None. All error conditions in Polypack routines are reported by means of an error-flag argument.

## See Also

Online: ppdipo, ppditr, ppinpo, ppintr, ppplcl, ppppap, ppunpo, 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.