lw_arc_side()

int lw_arc_side	(	const POINT2D *	A1,
		const POINT2D *	A2,
		const POINT2D *	A3,
		const POINT2D *	Q
	)

Definition at line 178 of file lwalgorithm.c.

References distance2d_pt_pt(), lw_arc_center(), and lw_segment_side().

Referenced by ptarrayarc_contains_point_partial().

{
        POINT2D C;
        double radius_A;
        double side_Q, side_A2;
        double d;

        side_Q = lw_segment_side(A1, A3, Q);
        radius_A = lw_arc_center(A1, A2, A3, &C);
        side_A2 = lw_segment_side(A1, A3, A2);

        /* Linear case */
        if ( radius_A < 0 )
                return side_Q;

        d = distance2d_pt_pt(Q, &C);

        /* Q is on the arc boundary */
        if ( d == radius_A && side_Q == side_A2 )
        {
                return 0;
        }

        /* Q on A1-A3 line, so its on opposite side to A2 */
        if ( side_Q == 0 )
        {
                return -1 * side_A2;
        }

        /*
        * Q is inside the arc boundary, so it's not on the side we
        * might think from examining only the end points
        */
        if ( d < radius_A && side_Q == side_A2 )
        {
                side_Q *= -1;
        }

        return side_Q;
}

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