# ncl_polypack (3) - Linux Manuals

## ncl_polypack: a set of routines allowing polygons to be manipulated in various

## NAME

Polypack - 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.## COPYRIGHT

Copyright (C) 1987-2009University Corporation for Atmospheric Research

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