segments_tcpa()

static double segments_tcpa ( POINT4D *  p0, const POINT4D *  p1, POINT4D *  q0, const POINT4D *  q1, double  t0, double  t1  )

static

Definition at line 981 of file lwlinearreferencing.c.

{
        POINT3DZ pv; /* velocity of p, aka u */
        POINT3DZ qv; /* velocity of q, aka v */
        POINT3DZ dv; /* velocity difference */
        POINT3DZ w0; /* vector between first points */
 
        /*
          lwnotice("FROM %g,%g,%g,%g -- %g,%g,%g,%g",
            p0->x, p0->y, p0->z, p0->m,
            p1->x, p1->y, p1->z, p1->m);
          lwnotice("  TO %g,%g,%g,%g -- %g,%g,%g,%g",
            q0->x, q0->y, q0->z, q0->m,
            q1->x, q1->y, q1->z, q1->m);
        */
 
        /* PV aka U */
        pv.x = (p1->x - p0->x);
        pv.y = (p1->y - p0->y);
        pv.z = (p1->z - p0->z);
        /*lwnotice("PV:  %g, %g, %g", pv.x, pv.y, pv.z);*/
 
        /* QV aka V */
        qv.x = (q1->x - q0->x);
        qv.y = (q1->y - q0->y);
        qv.z = (q1->z - q0->z);
        /*lwnotice("QV:  %g, %g, %g", qv.x, qv.y, qv.z);*/
 
        dv.x = pv.x - qv.x;
        dv.y = pv.y - qv.y;
        dv.z = pv.z - qv.z;
        /*lwnotice("DV:  %g, %g, %g", dv.x, dv.y, dv.z);*/
 
        double dv2 = DOT(dv, dv);
        /*lwnotice("DOT: %g", dv2);*/
 
        if (dv2 == 0.0)
        {
                /* Distance is the same at any time, we pick the earliest */
                return t0;
        }
 
        /* Distance at any given time, with t0 */
        w0.x = (p0->x - q0->x);
        w0.y = (p0->y - q0->y);
        w0.z = (p0->z - q0->z);
 
        /*lwnotice("W0:  %g, %g, %g", w0.x, w0.y, w0.z);*/
 
        /* Check that at distance dt w0 is distance */
 
        /* This is the fraction of measure difference */
        double t = -DOT(w0, dv) / dv2;
        /*lwnotice("CLOSEST TIME (fraction): %g", t);*/
 
        if (t > 1.0)
        {
                /* Getting closer as we move to the end */
                /*lwnotice("Converging");*/
                t = 1;
        }
        else if (t < 0.0)
        {
                /*lwnotice("Diverging");*/
                t = 0;
        }
 
        /* Interpolate the actual points now */
 
        p0->x += pv.x * t;
        p0->y += pv.y * t;
        p0->z += pv.z * t;
 
        q0->x += qv.x * t;
        q0->y += qv.y * t;
        q0->z += qv.z * t;
 
        t = t0 + (t1 - t0) * t;
        /*lwnotice("CLOSEST TIME (real): %g", t);*/
 
        return t;
}

References DOT, POINT3DZ::x, POINT4D::x, POINT3DZ::y, POINT4D::y, POINT3DZ::z, and POINT4D::z.

Referenced by lwgeom_cpa_within(), and lwgeom_tcpa().

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