PIP()

int PIP	(	Point	P,
		Point *	V,
		int	n
	)

PIP(): crossing number test for a point in a polygon input: P = a point, V[] = vertex points of a polygon V[n+1] with V[n]=V[0].

Returns

0 = outside, 1 = inside

Definition at line 417 of file shp2pgsql-core.c.

{
        int cn = 0;    /* the crossing number counter */
        int i;
 
        /* loop through all edges of the polygon */
        for (i = 0; i < n-1; i++)      /* edge from V[i] to V[i+1] */
        {
                if (((V[i].y <= P.y) && (V[i + 1].y > P.y))    /* an upward crossing */
                        || ((V[i].y > P.y) && (V[i + 1].y <= P.y)))   /* a downward crossing */
                {
                        double vt = (float)(P.y - V[i].y) / (V[i + 1].y - V[i].y);
                        if (P.x < V[i].x + vt * (V[i + 1].x - V[i].x)) /* P.x < intersect */
                                ++cn;   /* a valid crossing of y=P.y right of P.x */
                }
        }
 
        return (cn&1);    /* 0 if even (out), and 1 if odd (in) */
}

References struct_ring::n, struct_point::x, and struct_point::y.

Referenced by FindPolygons().

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