• # Point in a poly II

Math and Physics

From pdxgate!usenet.ee.pdx.edu!reed!henson!news.u.washington.edu!usenet.coe.montana.edu!caen!uunet!mcsun!sun4nl!bsoatr!bskewe!kewe Tue Mar 2 15:21:37 PST 1993

In article [email="douglasg@gr.hp.com"]douglasg@gr.hp.com[/email] writes:

>
> I'm looking for an algorithm which determines if a point
> falls within an arbitrary (convex or concave) polygon.
>
> Thanks,
>
> Douglas Gennetten
> Hewlett-Packard
>
>
>

BOOLEAN PointInsideOfPolygon ( POLYGOON *P, VECTOR2D *p ) { VECTOR2D o, v, w; INDEX ncross, N, n; ncros = 0; N = PolygonLength(P); /* Number of vertices */ GivePolygonVertex ( P, N, &o ); for ( n=1; n<=N; n++ ) { GivePolygonVertex ( P, n, &v ); if ( o.x >= p->x && v.x < p->x || o.x < p->x && v.x >= p->x ) { w.x = p->x; LinearInterpolation ( &o, &v, &w ); if ( w.x == p->x && w.y == p->y ) return(TRUE); else if ( w.y > p->y ) ncross++; } CopyVector2d ( &v, &o ); } if ( ncross%2 == 0 ) return(FALSE); else return(TRUE); }

Cornelis Wessels
kewe@bskewe.atr.bso.nl

Krommenoord 14
3079 ZT ROTTERDAM
The Netherlands
+31 - 10 - 4826394

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