ptarray_locate_point()

double ptarray_locate_point	(	const POINTARRAY *	pa,
		const POINT4D *	p4d,
		double *	mindistout,
		POINT4D *	proj4d
	)

Definition at line 1306 of file ptarray.c.

References closest_point_on_segment(), distance2d_pt_pt(), distance2d_pt_seg(), getPoint2d_cp(), getPoint4d_p(), LWDEBUG, LWDEBUGF, POINTARRAY::npoints, p2d_same(), ptarray_length_2d(), POINT2D::x, POINT4D::x, POINT2D::y, and POINT4D::y.

Referenced by lwgeom_interpolate_point(), LWGEOM_line_locate_point(), and test_ptarray_locate_point().

{
        double mindist=-1;
        double tlen, plen;
        int t, seg=-1;
        POINT4D start4d, end4d, projtmp;
        POINT2D proj, p;
        const POINT2D *start = NULL, *end = NULL;

        /* Initialize our 2D copy of the input parameter */
        p.x = p4d->x;
        p.y = p4d->y;

        if ( ! proj4d ) proj4d = &projtmp;

        start = getPoint2d_cp(pa, 0);

        /* If the pointarray has only one point, the nearest point is */
        /* just that point */
        if ( pa->npoints == 1 )
        {
                getPoint4d_p(pa, 0, proj4d);
                if ( mindistout )
                        *mindistout = distance2d_pt_pt(&p, start);
                return 0.0;
        }

        /* Loop through pointarray looking for nearest segment */
        for (t=1; t<pa->npoints; t++)
        {
                double dist;
                end = getPoint2d_cp(pa, t);
                dist = distance2d_pt_seg(&p, start, end);

                if (t==1 || dist < mindist )
                {
                        mindist = dist;
                        seg=t-1;
                }

                if ( mindist == 0 )
                {
                        LWDEBUG(3, "Breaking on mindist=0");
                        break;
                }

                start = end;
        }

        if ( mindistout ) *mindistout = mindist;

        LWDEBUGF(3, "Closest segment: %d", seg);
        LWDEBUGF(3, "mindist: %g", mindist);

        /*
         * We need to project the
         * point on the closest segment.
         */
        getPoint4d_p(pa, seg, &start4d);
        getPoint4d_p(pa, seg+1, &end4d);
        closest_point_on_segment(p4d, &start4d, &end4d, proj4d);

        /* Copy 4D values into 2D holder */
        proj.x = proj4d->x;
        proj.y = proj4d->y;

        LWDEBUGF(3, "Closest segment:%d, npoints:%d", seg, pa->npoints);

        /* For robustness, force 1 when closest point == endpoint */
        if ( (seg >= (pa->npoints-2)) && p2d_same(&proj, end) )
        {
                return 1.0;
        }

        LWDEBUGF(3, "Closest point on segment: %g,%g", proj.x, proj.y);

        tlen = ptarray_length_2d(pa);

        LWDEBUGF(3, "tlen %g", tlen);

        /* Location of any point on a zero-length line is 0 */
        /* See http://trac.osgeo.org/postgis/ticket/1772#comment:2 */
        if ( tlen == 0 ) return 0;

        plen=0;
        start = getPoint2d_cp(pa, 0);
        for (t=0; t<seg; t++, start=end)
        {
                end = getPoint2d_cp(pa, t+1);
                plen += distance2d_pt_pt(start, end);

                LWDEBUGF(4, "Segment %d made plen %g", t, plen);
        }

        plen+=distance2d_pt_pt(&proj, start);

        LWDEBUGF(3, "plen %g, tlen %g", plen, tlen);

        return plen/tlen;
}

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