• 07/16/99 05:58 PM
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    Point in a poly II

    Math and Physics

    Myopic Rhino
    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
    0


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