LWGEOM_line_interpolate_point()

Datum LWGEOM_line_interpolate_point

(

PG_FUNCTION_ARGS

)

Definition at line 153 of file lwgeom_functions_analytic.c.

References distance(), distance2d_pt_pt(), dumpnode::geom, geometry_serialize(), getPoint4d_p(), gserialized_get_srid(), gserialized_get_type(), gserialized_has_m(), gserialized_has_z(), gserialized_is_empty(), interpolate_point4d(), LINETYPE, lwgeom_as_lwline(), lwgeom_from_gserialized(), lwgeom_has_m(), lwgeom_has_z(), lwpoint_as_lwgeom(), lwpoint_construct(), lwpoint_construct_empty(), lwpoint_free(), POINTARRAY::npoints, LWLINE::points, ptarray_construct(), ptarray_length_2d(), ptarray_set_point4d(), and LWLINE::srid.

Referenced by LWGEOM_SetEffectiveArea().

{
        GSERIALIZED *gser = PG_GETARG_GSERIALIZED_P(0);
        GSERIALIZED *result;
        double distance = PG_GETARG_FLOAT8(1);
        LWLINE *line;
        LWGEOM *geom;
        LWPOINT *point;
        POINTARRAY *ipa, *opa;
        POINT4D pt;
        int nsegs, i;
        double length, slength, tlength;

        if ( distance < 0 || distance > 1 )
        {
                elog(ERROR,"line_interpolate_point: 2nd arg isn't within [0,1]");
                PG_RETURN_NULL();
        }

        if ( gserialized_get_type(gser) != LINETYPE )
        {
                elog(ERROR,"line_interpolate_point: 1st arg isn't a line");
                PG_RETURN_NULL();
        }

        /* Empty.InterpolatePoint == Point Empty */
        if ( gserialized_is_empty(gser) )
        {
                point = lwpoint_construct_empty(gserialized_get_srid(gser), gserialized_has_z(gser), gserialized_has_m(gser));
                result = geometry_serialize(lwpoint_as_lwgeom(point));
                lwpoint_free(point);
                PG_RETURN_POINTER(result);
        }

        geom = lwgeom_from_gserialized(gser);
        line = lwgeom_as_lwline(geom);
        ipa = line->points;

        /* If distance is one of the two extremes, return the point on that
         * end rather than doing any expensive computations
         */
        if ( distance == 0.0 || distance == 1.0 )
        {
                if ( distance == 0.0 )
                        getPoint4d_p(ipa, 0, &pt);
                else
                        getPoint4d_p(ipa, ipa->npoints-1, &pt);

                opa = ptarray_construct(lwgeom_has_z(geom), lwgeom_has_m(geom), 1);
                ptarray_set_point4d(opa, 0, &pt);

                point = lwpoint_construct(line->srid, NULL, opa);
                PG_RETURN_POINTER(geometry_serialize(lwpoint_as_lwgeom(point)));
        }

        /* Interpolate a point on the line */
        nsegs = ipa->npoints - 1;
        length = ptarray_length_2d(ipa);
        tlength = 0;
        for ( i = 0; i < nsegs; i++ )
        {
                POINT4D p1, p2;
                POINT4D *p1ptr=&p1, *p2ptr=&p2; /* don't break
                                                                                 * strict-aliasing rules
                                                                                 */

                getPoint4d_p(ipa, i, &p1);
                getPoint4d_p(ipa, i+1, &p2);

                /* Find the relative length of this segment */
                slength = distance2d_pt_pt((POINT2D*)p1ptr, (POINT2D*)p2ptr)/length;

                /* If our target distance is before the total length we've seen
                 * so far. create a new point some distance down the current
                 * segment.
                 */
                if ( distance < tlength + slength )
                {
                        double dseg = (distance - tlength) / slength;
                        interpolate_point4d(&p1, &p2, &pt, dseg);
                        opa = ptarray_construct(lwgeom_has_z(geom), lwgeom_has_m(geom), 1);
                        ptarray_set_point4d(opa, 0, &pt);
                        point = lwpoint_construct(line->srid, NULL, opa);
                        PG_RETURN_POINTER(geometry_serialize(lwpoint_as_lwgeom(point)));
                }
                tlength += slength;
        }

        /* Return the last point on the line. This shouldn't happen, but
         * could if there's some floating point rounding errors. */
        getPoint4d_p(ipa, ipa->npoints-1, &pt);
        opa = ptarray_construct(lwgeom_has_z(geom), lwgeom_has_m(geom), 1);
        ptarray_set_point4d(opa, 0, &pt);
        point = lwpoint_construct(line->srid, NULL, opa);
        PG_FREE_IF_COPY(gser, 0);
        PG_RETURN_POINTER(geometry_serialize(lwpoint_as_lwgeom(point)));
}

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