lw_dist3d_seg_seg()

int lw_dist3d_seg_seg	(	POINT3DZ *	s1p1,
		POINT3DZ *	s1p2,
		POINT3DZ *	s2p1,
		POINT3DZ *	s2p2,
		DISTPTS3D *	dl
	)

Finds the two closest points on two linesegments.

Definition at line 918 of file measures3d.c.

{
        VECTOR3D v1, v2, vl;
        double s1k, s2k; /*two variables representing where on Line 1 (s1k) and where on Line 2 (s2k) a connecting line between the two lines is perpendicular to both lines*/
        POINT3DZ p1, p2;
        double a, b, c, d, e, D;
 
        /*s1p1 and s1p2 are the same point */
        if (  ( s1p1->x == s1p2->x) && (s1p1->y == s1p2->y) && (s1p1->z == s1p2->z) )
        {
                return lw_dist3d_pt_seg(s1p1,s2p1,s2p2,dl);
        }
        /*s2p1 and s2p2 are the same point */
        if (  ( s2p1->x == s2p2->x) && (s2p1->y == s2p2->y) && (s2p1->z == s2p2->z) )
        {
                dl->twisted= ((dl->twisted) * (-1));
                return lw_dist3d_pt_seg(s2p1,s1p1,s1p2,dl);
        }
 
/*
        Here we use algorithm from softsurfer.com
        that can be found here
        http://softsurfer.com/Archive/algorithm_0106/algorithm_0106.htm
*/
 
        if (!get_3dvector_from_points(s1p1, s1p2, &v1))
                return LW_FALSE;
 
        if (!get_3dvector_from_points(s2p1, s2p2, &v2))
                return LW_FALSE;
 
        if (!get_3dvector_from_points(s2p1, s1p1, &vl))
                return LW_FALSE;
 
        a = DOT(v1,v1);
        b = DOT(v1,v2);
        c = DOT(v2,v2);
        d = DOT(v1,vl);
        e = DOT(v2,vl);
        D = a*c - b*b;
 
 
        if (D <0.000000001)
        {        /* the lines are almost parallel*/
                s1k = 0.0; /*If the lines are parallel we try by using the startpoint of first segment. If that gives a projected point on the second line outside segment 2 it wil be found that s2k is >1 or <0.*/
                if(b>c)   /* use the largest denominator*/
                {
                        s2k=d/b;
                }
                else
                {
                        s2k =e/c;
                }
        }
        else
        {
                s1k = (b*e - c*d) / D;
                s2k = (a*e - b*d) / D;
        }
 
        /* Now we check if the projected closest point on the infinite lines is outside our segments. If so the combinations with start and end points will be tested*/
        if(s1k<0.0||s1k>1.0||s2k<0.0||s2k>1.0)
        {
                if(s1k<0.0)
                {
 
                        if (!lw_dist3d_pt_seg(s1p1, s2p1, s2p2, dl))
                        {
                                return LW_FALSE;
                        }
                }
                if(s1k>1.0)
                {
 
                        if (!lw_dist3d_pt_seg(s1p2, s2p1, s2p2, dl))
                        {
                                return LW_FALSE;
                        }
                }
                if(s2k<0.0)
                {
                        dl->twisted= ((dl->twisted) * (-1));
                        if (!lw_dist3d_pt_seg(s2p1, s1p1, s1p2, dl))
                        {
                                return LW_FALSE;
                        }
                }
                if(s2k>1.0)
                {
                        dl->twisted= ((dl->twisted) * (-1));
                        if (!lw_dist3d_pt_seg(s2p2, s1p1, s1p2, dl))
                        {
                                return LW_FALSE;
                        }
                }
        }
        else
        {/*Find the closest point on the edges of both segments*/
                p1.x=s1p1->x+s1k*(s1p2->x-s1p1->x);
                p1.y=s1p1->y+s1k*(s1p2->y-s1p1->y);
                p1.z=s1p1->z+s1k*(s1p2->z-s1p1->z);
 
                p2.x=s2p1->x+s2k*(s2p2->x-s2p1->x);
                p2.y=s2p1->y+s2k*(s2p2->y-s2p1->y);
                p2.z=s2p1->z+s2k*(s2p2->z-s2p1->z);
 
                if (!lw_dist3d_pt_pt(&p1,&p2,dl))/* Send the closest points to point-point calculation*/
                {
                        return LW_FALSE;
                }
        }
        return LW_TRUE;
}

References DOT, get_3dvector_from_points(), lw_dist3d_pt_pt(), lw_dist3d_pt_seg(), LW_FALSE, LW_TRUE, DISTPTS3D::twisted, POINT3DZ::x, POINT3DZ::y, and POINT3DZ::z.

Referenced by lw_dist3d_ptarray_ptarray().

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