Returns the OdDb2dPolyline OCS position of this entity (DXF 10).

Each OdDb2dPolyline is described a series of OCS OdDb2dVertices and an elevation. 

While Z coordinates are set and retrieved by setPosition() and position() respectively, they are ignored by the Polyline. 

The elevation of the Polyline can be changed only with OdDb2dPolyline::setElevation().