distance2d_pt_seg()

double distance2d_pt_seg	(	const POINT2D *	p,
		const POINT2D *	A,
		const POINT2D *	B
	)

Definition at line 2332 of file measures.c.

{
        double  r,s;
 
        /*if start==end, then use pt distance */
        if (  ( A->x == B->x) && (A->y == B->y) )
                return distance2d_pt_pt(p,A);
 
        /*
         * otherwise, we use comp.graphics.algorithms
         * Frequently Asked Questions method
         *
         *  (1)               AC dot AB
                *         r = ---------
                *               ||AB||^2
         *      r has the following meaning:
         *      r=0 P = A
         *      r=1 P = B
         *      r<0 P is on the backward extension of AB
         *      r>1 P is on the forward extension of AB
         *      0<r<1 P is interior to AB
         */
 
        r = ( (p->x-A->x) * (B->x-A->x) + (p->y-A->y) * (B->y-A->y) )/( (B->x-A->x)*(B->x-A->x) +(B->y-A->y)*(B->y-A->y) );
 
        if (r<0) return distance2d_pt_pt(p,A);
        if (r>1) return distance2d_pt_pt(p,B);
 
 
        /*
         * (2)
         *           (Ay-Cy)(Bx-Ax)-(Ax-Cx)(By-Ay)
         *      s = -----------------------------
         *                      L^2
         *
         *      Then the distance from C to P = |s|*L.
         *
         */
 
        s = ( (A->y-p->y)*(B->x-A->x)- (A->x-p->x)*(B->y-A->y) ) /
            ( (B->x-A->x)*(B->x-A->x) +(B->y-A->y)*(B->y-A->y) );
 
        return FP_ABS(s) * sqrt(
                   (B->x-A->x)*(B->x-A->x) + (B->y-A->y)*(B->y-A->y)
               );
}

References distance2d_pt_pt(), FP_ABS, r, s, POINT2D::x, and POINT2D::y.

Referenced by lwline_split_by_point_to(), and ptarray_locate_point().

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