public void Init( string defaultZoneTypeName, string filename )
{
// delete ALL portals
portals.Clear();
// delete all the zones
zones.Clear();
frameCount = 0;
this.defaultZoneTypeName = defaultZoneTypeName;
defaultZoneFileName = filename;
// create a new default zone
zoneFactoryManager = PCZoneFactoryManager.Instance;
defaultZone = CreateZoneFromFile( this.defaultZoneTypeName, "Default_Zone", RootSceneNode as PCZSceneNode, defaultZoneFileName );
}