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