Real-time Transmission Of Solid Models In Collaborative Design

Integrated with the traditional CAD technology and CSCW technology, the collaborative CAD, which is able to shorten the product development time, make best use of remote resources and reduces the design cost, has made a rapid and further progress in the past decade. However, one of the key points of the collaborative CAD system, real-time data transmission of CAD model becomes a tough problem because of the complexity of CAD model. In order to make the collaboration more efficient, the incremental transmission technology is studied in this thesis.An incremental transmission algorithm based on 3D facet model is given, which is widely used in the central collaborative CAD system with thin clients. In the server, the accurate CAD model with Boundary Representation (B-rep) is translated to incremental 3D facet model. In the client, the received incremental model will be merged into the local facet model in real time. Also, a web-based collaborative design prototype system, WebCOSMOS, is implemented to certify the above algorithm of incremental transmission of facet model.A direct incremental transmission algorithm of Boundary Representation (B-rep) is developed according to the requirement of real-time transmission of accurate CAD model in replicated collaborative CAD systems. There are three steps in this algorithm. First, by comparing the model before one operation and the model after the operation, we get the incremental B-rep model. Second, encode the incremental model, transmit it over network, and decode it in the remote sites. Third, install the incremental B-rep model into local model and keep consistent the result B-rep model in all sites. In order to decrease the capacity of changed entities while guarantee the correct installation of this model in remote sites, the Topological Entity Hierarchy Chain is put forward to help construct the incremental model, which keeps the relations between topological entities as well as reduces the redundant information ofthe incremental model.In order to improve the practicability of direct incremental transmission algorithm of B-rep model, a method to deal with modification operations is given considering the difference between them and general creation or deletion operations. We propose an algorithm for identifying, encoding and installing geometrically changed entities, which is excused simultaneously with the transmission algorithm of incremental topological model. Due to the fact that the incremental B-rep model cannot be installed effectively after modification operations, we use an approach of operation shift to reconstruct the result model correctly.Finally, a replicated synchronized collaborative system, DIBS, is implemented. Meanwhile, several detailed synchronized collaborative design are performed on this prototype system. The validity of the direct incremental transmission algorithm of B-rep is certified and the transmitted data amounts of the above detail processes are provided to help analyze the efficiency of our algorithm.