1 / 41

A Trajectory-Preserving Synchronization Method for Collaborative Visualization

*. **. City University of Hong Kong. A Trajectory-Preserving Synchronization Method for Collaborative Visualization. Lewis W.F. Li* Frederick W.B. Li** Rynson W.H. Lau**. Overview. Introduction Related Work Methodology Experiment Results Conclusion. Part I. Introduction.

nardo
Download Presentation

A Trajectory-Preserving Synchronization Method for Collaborative Visualization

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. * ** City Universityof Hong Kong A Trajectory-Preserving Synchronization Method for Collaborative Visualization Lewis W.F. Li* Frederick W.B. Li** Rynson W.H. Lau**

  2. Overview • Introduction • Related Work • Methodology • Experiment Results • Conclusion

  3. Part I Introduction

  4. Introduction (1/2) • Collaborative visualization • Geographically separated users to be connected over the network to visualize and manipulate dataset for problem solving • Examples • Fluid dynamics visualization • Volume visualization • Medical data visualization

  5. Introduction (2/2) • Characteristics of collaborative visualization • User is allowed to interact with the visualization dataset continuously over time • Dataset updates should subsequently be distributed to remote users over the network • Problems • Due to network latency, each remote user may receive updates with a different amount of delay • User’s ability in performing desirable collaborative tasks will be affected, due to the induced view discrepancy among remote users

  6. Objectives of This Work • Provide a more synchronized view of visualization changes to collaborating users • Develop procedures to correct motion trajectories of dynamic objects • Prevent discontinuous motion • Address false positive and false negative collision detection problems

  7. Part II Related Work

  8. Related Work • Traditional Applications • Easy to work well provided that state updates are received by remote sites in a correct order • Time gap between two consecutive updates is typically large as compared to network latency • Collaborative Applications • State updates occurs continuously • Unfortunately, updates need to present to remote users timely or at least within a very short time • Existing solutions: - User or system side adaptation - Local Lag mechanism

  9. Part III Methodology

  10. Methodology • Relaxed Consistency Control Model • Gradual Synchronization • Trajectory-Preserving Synchronization

  11. Relaxed Consistency Control Model • Observation: Users generally pay more attention on the trajectory of dynamic objects rather than their individual states • Given that the states of a replicated object at two remote sites at time t are si(t) and sj(t), the state discrepancy D of the object between the two sites during any time period Ta and Tb should be smaller than an application specific tolerance, ξ. Hence,

  12. Gradual Synchronization (1/2)ACM Multimedia 2004 • Trade accuracy of individual state of a dynamic object for preserving their state trajectory • Run a reference simulator on the server for each object in a client-server environment • Note: 1st order simulator: 2nd order simulator: • When a client receive or initiate a new motion update of an object, the client will align the motion of the local object against its reference simulator

  13. Gradual Synchronization (2/2) ACM Multimedia 2004 • Contribution: • This method effectively reduces the latency of a client to obtain a state update from a double round-trip time delay to a single one • Limitation: • High discrepancy occurs between the period when an interaction has just occurred and before the update message reaches a remote client • Apparently, such discrepancy appears shortly for each time, but would become serious if interactions occur frequently

  14. Trajectory-Preserving Synchronization • Extends from our gradual synchronization method • Consider the characteristics of spatial changes and interactions of dynamic objects are affected by network latency • A set of procedures are developed to correct motion trajectory of dynamic objects • Handle false positive and false negative collision detection problem

  15. Client-Server Trajectory-Preserving Synchronization • Client A (avatar) and the server

  16. Client-ClientTrajectory-Preserving Synchronization • Server and client B (observer)

  17. Arbitrary MomentTrajectory-Preserving Synchronization • Client A (avatar) and the server

  18. Handling Object CollisionsTrajectory-Preserving Synchronization • Interpret the collision response as motion commands • Resolve inconsistent collision problem into two sets of simpler problems

  19. Handling Object CollisionTrajectory-Preserving Synchronization • False negative collisions • Collisions detected in the avatar but not in the server (case (b)) • Inhabit the avatar to perform collision detection until motion remediation process has finished • False positive collisions • Collisions detected in the server but not in the observer (case (f)) • Inhabit the observer to perform collision detection until motion remediation process has finished

  20. Part IV Experiment Results

  21. Experiment I (1/4) • Demonstrate user’s navigation at an avatar, the serverand an observer • Compare the performance of different methods • Dead Reckoning • Original method • New Method • Here, focus on comparing dead reckoning and the new method only • Full and other Demos • http://www.cs.cityu.edu.hk/~kwfli/vis2006/vis.html

  22. Experiment I (2/4) • Dead Reckoning

  23. Experiment I (3/4) • New Method

  24. Experiment I (4/4) • Focus on comparing several motion changes Dead Reckoning New Method

  25. Experiment II (1/5) • Focus on the motion of selected object (the green ball) in the virtual environment • Compare the position discrepancy in between • Client A and the server • The server and client B • Client A and client B

  26. Experiment II (2/5) • Screen shots of our prototype for collaborative visualization

  27. Experiment II (3/5) • Client A and the server

  28. Experiment II (4/5) • The server and client B

  29. Experiment II (5/5) • Client A and client B

  30. Experiment III (1/3) • Focus on the accuracy of the new method in handling object collisions • Compare the position discrepancy between server and four users with different network latencies

  31. Experiment III (2/3)

  32. Experiment III (3/3)

  33. Part V Conclusion

  34. Conclusion (1/2) • Propose a trajectory-preserving synchronization method to support collaborative visualization • Handle unpredictable user changes • Handle collision detection problem

  35. Conclusion (2/2) • Limitations • Assume using connection-oriented network • Message loss is not considered • Future Works • Consider difference types of network • Support haptic interface and rendering

  36. Thank you! Contacts Lewis Li: kwfli@cs.cityu.edu.hk Frederick Li: Frederick.Li@durham.ac.uk Rynson Lau: Rynson.Lau@durham.ac.uk Questions and Answers http://www.cs.cityu.edu.hk/~kwfli/vis2006/

  37. Appendix Clock Synchronization • Two common approaches • Backward correction • Forward correction

  38. Appendix Dead Reckoning • Client A and client B

  39. AppendixGradual Synchronization • For each motion • Motion timers Ts and Tc are maintained at the server and client simulator, respectively • Assume position updates in every Δt • Estimate the round-trip time, Test • Adjust every Δt in client for Tc based on Test • Synchronized when Tc is the same as Ts

  40. AppendixGradual Synchronization • Client A and the server

  41. AppendixGradual Synchronization • Server and client B

More Related