Compression and Coding of Large CAD Models

In this paper we introduce a compression scheme suitable for large CAD (Computer Aided Design) models. We assume as input a large model in IGES 1 and VRML 2 formats that encode e ciently and transmit to a client for remote display and modeling. To this end we focus on two main issues: (a) space e cient encoding of IGES and VRML les, (b) fragmentation of the compressed model into small independent units that can be transmitted incrementally over unreliable data communication media. We extend previously published compression schemes to handle quadrilateral and general polygonal models still maintaining the layering structure used to organize the redundant information of the geometric model. In particular we implement polygon strips to handle general polyhedral meshes and we merge them together so that non-manifold geometry are also allowed. NURBS 3 patches are encoded as quadrilaterals with properties attached. The compressed output is a bit-stream partitioned into variable length blocks which can be transmitted independently. With this structure the transmission can be performed on a unreliable network allowing minimal retransmission in case of lost or corrupted blocks