Incremental Transmission of B-Rep based CAD Models for Collaborative Design Environment

1. Incremental Transmission of B-Rep based CAD Models for Collaborative Design Environment Efficient Streaming Algorithm for B-Rep based CAD Models through the Network Youngjae Song, CAD Lab. @ SNU

2. Introduction • Importance of the Transmission of CAD data • Play a key role in Concurrent Design environment. • Utilize the limitation of Network bandwidth. • Decrease the latency during design activity. • Strategies for solving the problem • Minimize the file size of CAD data • Geometry compression • Cut down the Latency for transmission of data • Incremental transmission • Avoid the security problem during the transmission • Data encryption / Digital Water-marking

3. Proposed Algorithm • Framework of the proposed approach CAD Data Server Client system CAD Data In App “A” B-Rep In App “B” Plug-in For App “A” Plug-in For App “B” B-Rep Interaction Security info. Other info. Preprocessing Reconstruction Incremental Block tree Internet Sequencing Data Encryption Data decryption Composing Data Block

4. Model Preprocessing • Apply the “Wrap-around” operation • Search the concave edges, identify the concave faces • Remove the complexity(concave region and hole) in the body. • Get the more simplified model with applying “Wrap-around”

5. Same area Same area Same area faceset1 faceset2 faceset3 faceset1 faceset2 faceset3 faceset4 faceset5 Model Preprocessing • Preprocessing Result • Define a set of concave faces(composing a distinct concave region or simple hole, pocket) as “FaceSet”. • Sub-group the facesets having the same area into parent group. Incremental Block Tree

6. Same area Same area Same area faceset1 faceset2 faceset3 faceset1 faceset2 faceset3 faceset4 faceset5 Sequencing the block tree • Determine the order to send data • Very simple & efficient compared to the other algorithms. • Sort the ‘Incremental Block Tree’ with area-ascending order. • Remove the facesets with area-ascending order. • At first send the most simplified body, and send the facesets to clients with area-decending order. Incremental Block Tree

7. Model Reconstruction • Reverse operation of Sequencing. • Apply the Reverse “Wrap-around” operation. • Reconstruct the shape data from the received data block. • Sequentially, apply the reconstruction process.

8. Model Reconstruction • Reconstruct the original model. • If User don’t want see the model more in detail, he can stop receiving the data from server immediately. -> Cut down the latency over the network. Reconstruct the original detailed model from simple model with the incremental data

9. Example #1 • Engine Piston (Server Program)

10. Example #1 • Result Table

11. Example #2 • Pad tray

12. Example #2 • Result Table

13. Data size to transfer at a time • Single fragment of sheet body is too small ; Compared to the capability of the high speed network. ; Too much overhead for the transmission. • Whole group of sheet bodies is sometimes too big. • Efficient scheduling algorithm to determine the size of the data to be transmitted at a time.

14. How to transmit the data ? • Transferring the native file data • Easy to implement. (currently implemented) • Overhead for the file format. • Additional operation is necessary. • Create the new file format • Minimize the overhead for transmitting data. • Hard to implement. • Pass the instruction to create the same geometry data in the client.

15. Future Work • More complex examples. • New data format for B-rep model data transmission. • Implementation of scheduling algorithm to construct the optimal size of data fragment for data transmission.