= Creating Topo Geometry Objects =


Currently, [wiki:UsersWikiTopoGeometry TopoGeometry] objects can only be defined by specifying their
component topology elements. We do support both basic !TopoGeometry
and hierarchical !TopoGeometry. Basic !TopoGeometry objects are those
composed by base topolocal elements (faces, edges, nodes). Hierarchical
!TopoGeometry objects are composed by other !TopoGeometry objects.

Each !TopoGeometry object belongs to a specific Layer of a specific
Topology. Before creating a !TopoGeometry object you need to create
its !TopologyLayer. A Topology Layer is an association of
a feature-table with the topology. It also contain type and hierarchy
information. We create a layer using the !AddTopoGeometryColumn() function:
     
{{{
topology.AddTopoGeometryColumn(topology_name,
                schema_name, table_name, column_name, feature_type,
                [child_layer])
}}}

The function will both add the requested column to the table and add
a record to the topology.layer table with all the given info.

If you don't specify [child_layer] (or set it to NULL) this layer
would contain Basic !TopoGeometries (composed by primitive topology
elements). Otherwise this layer will contain hierarchical !TopoGeometries
(composed by !TopoGeometries from the child_layer).

Once the layer is created (it's id is returned by the !AddTopoGeometryColumn
function) you're ready to construct !TopoGeometry objects in it:

        
{{{
topology.CreateTopoGeom(
                topology_name,
                feature_type,   -- 1:(multi)point, 2:(multi)line,
                                -- 3:(multi)poly, 4:collection
                layer_id,       -- as returned by AddTopoGeometryColumn
                TopoElementArray
        );
}}}