lwgeom_cpa_within()

int lwgeom_cpa_within	(	const LWGEOM *	g1,
		const LWGEOM *	g2,
		double	maxdist
	)

Is the closest point of approach within a distance ?

Returns

LW_TRUE or LW_FALSE

Definition at line 1311 of file lwlinearreferencing.c.

{
        LWLINE *l1, *l2;
        int i;
        GBOX gbox1, gbox2;
        double tmin, tmax;
        double *mvals;
        int nmvals = 0;
        double maxdist2 = maxdist * maxdist;
        int within = LW_FALSE;
 
        if (!lwgeom_has_m(g1) || !lwgeom_has_m(g2))
        {
                lwerror("Both input geometries must have a measure dimension");
                return LW_FALSE;
        }
 
        l1 = lwgeom_as_lwline(g1);
        l2 = lwgeom_as_lwline(g2);
 
        if (!l1 || !l2)
        {
                lwerror("Both input geometries must be linestrings");
                return LW_FALSE;
        }
 
        if (l1->points->npoints < 2 || l2->points->npoints < 2)
        {
                /* TODO: return distance between these two points */
                lwerror("Both input lines must have at least 2 points");
                return LW_FALSE;
        }
 
        /* We use lwgeom_calculate_gbox() instead of lwgeom_get_gbox() */
        /* because we cannot afford the float rounding inaccuracy when */
        /* we compare the ranges for overlap below */
        lwgeom_calculate_gbox(g1, &gbox1);
        lwgeom_calculate_gbox(g2, &gbox2);
 
        /*
         * Find overlapping M range
         * WARNING: may be larger than the real one
         */
 
        tmin = FP_MAX(gbox1.mmin, gbox2.mmin);
        tmax = FP_MIN(gbox1.mmax, gbox2.mmax);
 
        if (tmax < tmin)
        {
                LWDEBUG(1, "Inputs never exist at the same time");
                return LW_FALSE;
        }
 
        /*
         * Collect M values in common time range from inputs
         */
 
        mvals = lwalloc(sizeof(double) * (l1->points->npoints + l2->points->npoints));
 
        /* TODO: also clip the lines ? */
        nmvals = ptarray_collect_mvals(l1->points, tmin, tmax, mvals);
        nmvals += ptarray_collect_mvals(l2->points, tmin, tmax, mvals + nmvals);
 
        /* Sort values in ascending order */
        qsort(mvals, nmvals, sizeof(double), compare_double);
 
        /* Remove duplicated values */
        nmvals = uniq(mvals, nmvals);
 
        if (nmvals < 2)
        {
                /* there's a single time, must be that one... */
                double t0 = mvals[0];
                POINT4D p0, p1;
                LWDEBUGF(1, "Inputs only exist both at a single time (%g)", t0);
                if (-1 == ptarray_locate_along_linear(l1->points, t0, &p0, 0))
                {
                        lwnotice("Could not find point with M=%g on first geom", t0);
                        return LW_FALSE;
                }
                if (-1 == ptarray_locate_along_linear(l2->points, t0, &p1, 0))
                {
                        lwnotice("Could not find point with M=%g on second geom", t0);
                        return LW_FALSE;
                }
                if (distance3d_pt_pt((POINT3D *)&p0, (POINT3D *)&p1) <= maxdist)
                        within = LW_TRUE;
                lwfree(mvals);
                return within;
        }
 
        /*
         * For each consecutive pair of measures, compute time of closest point
         * approach and actual distance between points at that time
         */
        for (i = 1; i < nmvals; ++i)
        {
                double t0 = mvals[i - 1];
                double t1 = mvals[i];
#if POSTGIS_DEBUG_LEVEL >= 1
                double t;
#endif
                POINT4D p0, p1, q0, q1;
                int seg;
                double dist2;
 
                // lwnotice("T %g-%g", t0, t1);
 
                seg = ptarray_locate_along_linear(l1->points, t0, &p0, 0);
                if (-1 == seg)
                        continue; /* possible, if GBOX is approximated */
                // lwnotice("Measure %g on segment %d of line 1: %g, %g, %g", t0, seg, p0.x, p0.y, p0.z);
 
                seg = ptarray_locate_along_linear(l1->points, t1, &p1, seg);
                if (-1 == seg)
                        continue; /* possible, if GBOX is approximated */
                // lwnotice("Measure %g on segment %d of line 1: %g, %g, %g", t1, seg, p1.x, p1.y, p1.z);
 
                seg = ptarray_locate_along_linear(l2->points, t0, &q0, 0);
                if (-1 == seg)
                        continue; /* possible, if GBOX is approximated */
                // lwnotice("Measure %g on segment %d of line 2: %g, %g, %g", t0, seg, q0.x, q0.y, q0.z);
 
                seg = ptarray_locate_along_linear(l2->points, t1, &q1, seg);
                if (-1 == seg)
                        continue; /* possible, if GBOX is approximated */
                        // lwnotice("Measure %g on segment %d of line 2: %g, %g, %g", t1, seg, q1.x, q1.y, q1.z);
 
#if POSTGIS_DEBUG_LEVEL >= 1
                t =
#endif
                    segments_tcpa(&p0, &p1, &q0, &q1, t0, t1);
 
                /*
                lwnotice("Closest points: %g,%g,%g and %g,%g,%g at time %g",
                p0.x, p0.y, p0.z,
                q0.x, q0.y, q0.z, t);
                */
 
                dist2 = (q0.x - p0.x) * (q0.x - p0.x) + (q0.y - p0.y) * (q0.y - p0.y) + (q0.z - p0.z) * (q0.z - p0.z);
                if (dist2 <= maxdist2)
                {
                        LWDEBUGF(1, "Within distance %g at time %g, breaking", sqrt(dist2), t);
                        within = LW_TRUE;
                        break;
                }
        }
 
        /*
         * Release memory
         */
 
        lwfree(mvals);
 
        return within;
}

References compare_double(), distance3d_pt_pt(), FP_MAX, FP_MIN, LW_FALSE, LW_TRUE, lwalloc(), LWDEBUG, LWDEBUGF, lwerror(), lwfree(), lwgeom_as_lwline(), lwgeom_calculate_gbox(), lwgeom_has_m(), lwnotice(), GBOX::mmax, GBOX::mmin, POINTARRAY::npoints, LWLINE::points, ptarray_collect_mvals(), ptarray_locate_along_linear(), segments_tcpa(), uniq(), within(), POINT4D::x, POINT4D::y, and POINT4D::z.

Referenced by ST_CPAWithin(), and test_lwgeom_tcpa().

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