lw_dist2d_pt_arc()

int lw_dist2d_pt_arc	(	const POINT2D *	P,
		const POINT2D *	A1,
		const POINT2D *	A2,
		const POINT2D *	A3,
		DISTPTS *	dl
	)

Definition at line 1435 of file measures.c.

References DISTPTS::distance, distance2d_pt_pt(), FP_EQUALS, lw_arc_center(), lw_arc_is_pt(), lw_dist2d_arc_arc_concentric(), lw_dist2d_pt_pt(), lw_dist2d_pt_seg(), lw_pt_in_arc(), LW_TRUE, lwerror(), DISTPTS::mode, DISTPTS::p1, DISTPTS::p2, p2d_same(), POINT2D::x, and POINT2D::y.

Referenced by lw_dist2d_arc_arc(), lw_dist2d_pt_ptarrayarc(), lw_dist2d_seg_arc(), and test_lw_dist2d_pt_arc().

{
        double radius_A, d;
        POINT2D C; /* center of circle defined by arc A */
        POINT2D X; /* point circle(A) where line from C to P crosses */

        if ( dl->mode < 0 )
                lwerror("lw_dist2d_pt_arc does not support maxdistance mode");

        /* What if the arc is a point? */
        if ( lw_arc_is_pt(A1, A2, A3) )
                return lw_dist2d_pt_pt(P, A1, dl);

        /* Calculate centers and radii of circles. */
        radius_A = lw_arc_center(A1, A2, A3, &C);

        /* This "arc" is actually a line (A2 is colinear with A1,A3) */
        if ( radius_A < 0.0 )
                return lw_dist2d_pt_seg(P, A1, A3, dl);

        /* Distance from point to center */
        d = distance2d_pt_pt(&C, P);

        /* P is the center of the circle */
        if ( FP_EQUALS(d, 0.0) )
        {
                dl->distance = radius_A;
                dl->p1 = *A1;
                dl->p2 = *P;
                return LW_TRUE;
        }

        /* X is the point on the circle where the line from P to C crosses */
        X.x = C.x + (P->x - C.x) * radius_A / d;
        X.y = C.y + (P->y - C.y) * radius_A / d;

        /* Is crossing point inside the arc? Or arc is actually circle? */
        if ( p2d_same(A1, A3) || lw_pt_in_arc(&X, A1, A2, A3) )
        {
                lw_dist2d_pt_pt(P, &X, dl);
        }
        else
        {
                /* Distance is the minimum of the distances to the arc end points */
                lw_dist2d_pt_pt(A1, P, dl);
                lw_dist2d_pt_pt(A3, P, dl);
        }
        return LW_TRUE;
}

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