lwcollection_extract()

LWCOLLECTION * lwcollection_extract	(	LWCOLLECTION *	col,
		int	type
	)

Takes a potentially heterogeneous collection and returns a homogeneous collection consisting only of the specified type.

WARNING: the output will contain references to geometries in the input, so the result must be carefully released, not freed.

Definition at line 387 of file lwcollection.c.

{
        uint32_t i = 0;
        LWGEOM** geomlist;
        LWCOLLECTION* outcol;
        int geomlistsize = 16;
        int geomlistlen = 0;
        uint8_t outtype;
 
        if (!col) return NULL;
 
        switch (type)
        {
        case POINTTYPE:
                outtype = MULTIPOINTTYPE;
                break;
        case LINETYPE:
                outtype = MULTILINETYPE;
                break;
        case POLYGONTYPE:
                outtype = MULTIPOLYGONTYPE;
                break;
        default:
                lwerror(
                    "Only POLYGON, LINESTRING and POINT are supported by "
                    "lwcollection_extract. %s requested.",
                    lwtype_name(type));
                return NULL;
        }
 
        geomlist = lwalloc(sizeof(LWGEOM*) * geomlistsize);
 
        /* Process each sub-geometry */
        for (i = 0; i < col->ngeoms; i++)
        {
                int subtype = col->geoms[i]->type;
                /* Don't bother adding empty sub-geometries */
                if (lwgeom_is_empty(col->geoms[i])) continue;
                /* Copy our sub-types into the output list */
                if (subtype == type)
                {
                        /* We've over-run our buffer, double the memory segment
                         */
                        if (geomlistlen == geomlistsize)
                        {
                                geomlistsize *= 2;
                                geomlist = lwrealloc(
                                    geomlist, sizeof(LWGEOM*) * geomlistsize);
                        }
                        geomlist[geomlistlen] = lwgeom_clone(col->geoms[i]);
                        geomlistlen++;
                }
                /* Recurse into sub-collections */
                if (lwtype_is_collection(subtype))
                {
                        uint32_t j = 0;
                        LWCOLLECTION* tmpcol = lwcollection_extract(
                            (LWCOLLECTION*)col->geoms[i], type);
                        for (j = 0; j < tmpcol->ngeoms; j++)
                        {
                                /* We've over-run our buffer, double the memory
                                 * segment */
                                if (geomlistlen == geomlistsize)
                                {
                                        geomlistsize *= 2;
                                        geomlist = lwrealloc(geomlist,
                                                             sizeof(LWGEOM*) *
                                                                 geomlistsize);
                                }
                                geomlist[geomlistlen] = tmpcol->geoms[j];
                                geomlistlen++;
                        }
                        if (tmpcol->ngeoms) lwfree(tmpcol->geoms);
                        if (tmpcol->bbox) lwfree(tmpcol->bbox);
                        lwfree(tmpcol);
                }
        }
 
        if (geomlistlen > 0)
        {
                GBOX gbox;
                outcol = lwcollection_construct(
                    outtype, col->srid, NULL, geomlistlen, geomlist);
                lwgeom_calculate_gbox((LWGEOM*)outcol, &gbox);
                outcol->bbox = gbox_copy(&gbox);
        }
        else
        {
                lwfree(geomlist);
                outcol = lwcollection_construct_empty(outtype,
                                                      col->srid,
                                                      FLAGS_GET_Z(col->flags),
                                                      FLAGS_GET_M(col->flags));
        }
 
        return outcol;
}

References LWGEOM::bbox, LWCOLLECTION::bbox, LWCOLLECTION::flags, FLAGS_GET_M, FLAGS_GET_Z, gbox_copy(), LWCOLLECTION::geoms, LINETYPE, lwalloc(), lwcollection_construct(), lwcollection_construct_empty(), lwcollection_extract(), lwerror(), lwfree(), lwgeom_calculate_gbox(), lwgeom_clone(), lwgeom_is_empty(), lwrealloc(), lwtype_is_collection(), lwtype_name(), MULTILINETYPE, MULTIPOINTTYPE, MULTIPOLYGONTYPE, LWCOLLECTION::ngeoms, POINTTYPE, POLYGONTYPE, LWCOLLECTION::srid, and LWGEOM::type.

Referenced by _lwt_AddLineEdge(), lwcollection_extract(), lwgeom_to_basic_type(), ST_CollectionExtract(), and test_lwcollection_extract().

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