Bill Of Materials is a table that holds all parts and components with corresponding data and attributes. The logical representation is quite easy to understand but the physical data model of a BOM table is a complex concept that includes components, parts and data containers.
Teigha BIM supports external parameter definitions, which are entities stored in external text files and not included in project/family documents but can be imported into documents. Parameter elements of the ParamElemExternal class store the guid of an external parameter definition.
There are two ways of drawing feature lines: by 2D polyline (OdDbPolyline object) and by 3D polyline (OdDb3dPolyline object). The difference in elevation values affects all site feature edge points. If all elevations are equal, the feature line will be drawn via an OdDbPolyline entity, else via OdDb3dPolyline. In the 2D case, OdDbPolyline consists of eLine and eArc edges of type (AECCSiteEdge::Type). The OdDb3dPolyline entity consists of eLine types only and for arcs interpolation purposes uses tessellation (short, straight line segments) based on explode functionalities.