A simple en,ex marking rule for degenerate intersection points in 2D polygon clipping

TL;DR

This paper introduces a straightforward en,ex marking rule for degenerate intersection points in 2D polygon clipping, enhancing existing algorithms by handling special cases with minimal local geometric information.

Contribution

It extends the Greiner & Hormann algorithm to include degenerate intersections without requiring a new intersection detection method.

Findings

Handles degenerate intersections effectively

Integrates seamlessly with existing polygon clipping algorithms

Requires only local geometric information

Abstract

A simple en,ex rule to mark the intersection points of 2D input polygon contours separating the polygon interior from its exterior in the vicinity of the intersections is presented. Its form is close to the original Greiner & Hormann algorithm rule but encompasses degenerate intersections that are not self-intersections. It only uses local geometric information once the hand of the two input contours is known. The approach foundation is the distinction between two features of the studied intersections: the geometric intersection point and the assembling/concatenation point of the result contour/border. No special form of the intersection finding procedure is required.