Changeset 4847 for trunk/liblwgeom/lwcollection.c

Timestamp:

11/17/09 12:03:50 (3 years ago)

Author:

pramsey

Message:

Implement ST_CollectionExtract() to pull specific homogeneous collections out of heterogeneous collections. Regressions and documentation included. (#218)

Files:

• trunk/liblwgeom/lwcollection.c (modified) (1 diff)

trunk/liblwgeom/lwcollection.c

@@ -558 +558 @@
         return boxfinal;
 }
+
+/**
+* Takes a potentially heterogeneous collection and returns a homogeneous
+* collection consisting only of the specified type.
+*/
+LWCOLLECTION* lwcollection_extract(LWCOLLECTION *col, int type)
+{
+        int i = 0;
+        LWGEOM **geomlist;
+        BOX3D *b3d;
+        LWCOLLECTION *outcol;
+        int geomlistsize = 16;
+        int geomlistlen = 0;
+        uchar 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.", lwgeom_typename(type));
+                        return NULL;
+        }
+        
+        geomlist = lwalloc(sizeof(LWGEOM*) * geomlistsize);
+
+        /* Process each sub-geometry */
+        for( i = 0; i < col->ngeoms; i++ )
+        {
+                int subtype = TYPE_GETTYPE(col->geoms[i]->type);
+                /* 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] = col->geoms[i];
+                        geomlistlen++;
+                }
+                if( lwgeom_is_collection( subtype ) )
+                {
+                        int 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++;
+                        }
+                        lwfree(tmpcol);
+                }
+        }
+        
+        if( geomlistlen > 0 )
+        {
+                outcol = lwcollection_construct(outtype, col->SRID, NULL, geomlistlen, geomlist);       
+                b3d = lwcollection_compute_box3d(outcol);
+                outcol->bbox = box3d_to_box2df(b3d);
+        }
+        else
+        {
+                outcol = lwcollection_construct_empty(col->SRID, TYPE_HASZ(col->type), TYPE_HASM(col->type));
+        }
+        
+        return outcol;
+}
+