A Method for Object Reference in Collaborative Modeling System

In order to support natural and free multi-user interaction, a replicated architecture and optimistic concurrency control are adopted in collaborative 3D modeling system. On the one hand, topological elements in the geometric model are referred as operation parameters to define a completed modeling operation which is exchanged and executed among replicated sites. Only when topological objects of the geometric model are correctly referred, can the modeling operations be executed with a correct result. On the other hand, optimistic concurrency control will lead to geometric model inconsistency between the moment of reference generation in local site and moment of reference use in remote sites. The inconsistency will lead to incorrect naming and consequently the failure of object reference. In this paper, the functions of referred topological elements are analyzed and referred objects are categorized into replaceable ones and irreplaceable ones. For replaceable object reference, temporary geometric model is constructed to guarantee the correct object reference by providing the geometric information needed for positioning purposes. For irreplaceable object reference, geometric model is restored and object reference applied, finally redo all the concurrency operations undone during model restoration procedure. The proposed method has been implemented in a prototype system and it works well.