LWGEOM_envelope()

Datum LWGEOM_envelope

(

PG_FUNCTION_ARGS

)

Definition at line 1703 of file lwgeom_functions_basic.c.

{
        GSERIALIZED *geom = PG_GETARG_GSERIALIZED_P(0);
        LWGEOM *lwgeom = lwgeom_from_gserialized(geom);
        int srid = lwgeom->srid;
        POINT4D pt;
        GBOX box;
        POINTARRAY *pa;
        GSERIALIZED *result;
 
 
        if ( lwgeom_is_empty(lwgeom) )
        {
                /* must be the EMPTY geometry */
                PG_RETURN_POINTER(geom);
        }
 
        if ( lwgeom_calculate_gbox(lwgeom, &box) == LW_FAILURE )
        {
                /* must be the EMPTY geometry */
                PG_RETURN_POINTER(geom);
        }
 
        /*
         * Alter envelope type so that a valid geometry is always
         * returned depending upon the size of the geometry. The
         * code makes the following assumptions:
         *     - If the bounding box is a single point then return a
         *     POINT geometry
         *     - If the bounding box represents either a horizontal or
         *     vertical line, return a LINESTRING geometry
         *     - Otherwise return a POLYGON
         */
 
        if ( (box.xmin == box.xmax) && (box.ymin == box.ymax) )
        {
                /* Construct and serialize point */
                LWPOINT *point = lwpoint_make2d(srid, box.xmin, box.ymin);
                result = geometry_serialize(lwpoint_as_lwgeom(point));
                lwpoint_free(point);
        }
        else if ( (box.xmin == box.xmax) || (box.ymin == box.ymax) )
        {
                LWLINE *line;
                /* Construct point array */
                pa = ptarray_construct_empty(0, 0, 2);
 
                /* Assign coordinates to POINT2D array */
                pt.x = box.xmin;
                pt.y = box.ymin;
                ptarray_append_point(pa, &pt, LW_TRUE);
                pt.x = box.xmax;
                pt.y = box.ymax;
                ptarray_append_point(pa, &pt, LW_TRUE);
 
                /* Construct and serialize linestring */
                line = lwline_construct(srid, NULL, pa);
                result = geometry_serialize(lwline_as_lwgeom(line));
                lwline_free(line);
        }
        else
        {
                LWPOLY *poly;
                POINTARRAY **ppa = lwalloc(sizeof(POINTARRAY*));
                pa = ptarray_construct_empty(0, 0, 5);
                ppa[0] = pa;
 
                /* Assign coordinates to POINT2D array */
                pt.x = box.xmin;
                pt.y = box.ymin;
                ptarray_append_point(pa, &pt, LW_TRUE);
                pt.x = box.xmin;
                pt.y = box.ymax;
                ptarray_append_point(pa, &pt, LW_TRUE);
                pt.x = box.xmax;
                pt.y = box.ymax;
                ptarray_append_point(pa, &pt, LW_TRUE);
                pt.x = box.xmax;
                pt.y = box.ymin;
                ptarray_append_point(pa, &pt, LW_TRUE);
                pt.x = box.xmin;
                pt.y = box.ymin;
                ptarray_append_point(pa, &pt, LW_TRUE);
 
                /* Construct polygon  */
                poly = lwpoly_construct(srid, NULL, 1, ppa);
                result = geometry_serialize(lwpoly_as_lwgeom(poly));
                lwpoly_free(poly);
        }
 
        PG_FREE_IF_COPY(geom, 0);
 
        PG_RETURN_POINTER(result);
}

References geometry_serialize(), LW_FAILURE, LW_TRUE, lwalloc(), lwgeom_calculate_gbox(), lwgeom_from_gserialized(), lwgeom_is_empty(), lwline_as_lwgeom(), lwline_construct(), lwline_free(), lwpoint_as_lwgeom(), lwpoint_free(), lwpoint_make2d(), lwpoly_as_lwgeom(), lwpoly_construct(), lwpoly_free(), ptarray_append_point(), ptarray_construct_empty(), LWGEOM::srid, POINT4D::x, GBOX::xmax, GBOX::xmin, POINT4D::y, GBOX::ymax, and GBOX::ymin.

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