Webbased Collaborative 3D Modeling

1
Web-based Collaborative 3D Modeling

• Alex DeCastro
• San Diego Supercomputer Center
• University of California, San Diego
• Department of Computer Science
• University of California, Santa Barbara
• June 16, 1999

2
Presentation Outline

• Objective and Design Goals
• Project Description
• Future Work
• Conclusions
• Demo

3
Objective

• Develop a Web-based environment for multiple
  users to interactively construct a shared 3D
  model

4
Design Goals

• Leverage Web-based technology to perform 3D
  modeling
• Network architecture provides reliable and
  scalable message delivery between the clients
• Communication protocol allows a high-level of
  interaction between the users

5
Project Description

• Outline
• 3D Modeling Applet
• Object Server
• Proxy
• Network Architecture
• Communication Protocol

6
3D Modeling Applet

• Construct a 3D model
• Two different implementations
• Java3D Client
• VRML - JavaEAI Client

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Java3D Modeling Applet

• Java3D is a general 3D graphics API.
• Single-user applet
• Create, Delete, Select and Transform shapes
• Multi-user environment
• Create and Delete messages
• Lock and Unlock messages
• Transformation messages

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VRML - JavaEAI Applet

• VRML
• Virtual Reality Modeling Language
• JavaEAI
• External Authoring Interface
• Tiny3D is an existing 3D modeling applet
• Modified Tiny3D
• Added Delete object
• Changed the GUI
• Added client-side communication

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Inter-Applet Coordination

• Once the 3D modeling applets were completed
• Need some way to coordinate activity between the
  clients
• This is accomplished using a centralized
  coordinator Object Server

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Object Server

• Services Provided
• Forwards messages between the clients
• Coordinates communication between the clients
• Maintains the shared 3D model

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Object Server
HTTP Server
Object Database

• Simple network architecture
• Object Server running on HTTP server
• All clients connect to the object server

Object Server
TCP/IP Socket
TCP/IP Socket
Browser
Browser
Client Applet
Client Applet
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Proxy
Object Database

• Proxy provides greater flexibility
• Message forwarding agent between each client and
  the object server
• TCP/IP sockets provide reliable message delivery

Object Server
TCP/IP Socket
TCP/IP Socket
HTTP Server
HTTP Server
Proxy
Proxy
TCP/IP Socket
TCP/IP Socket
Browser
Browser
Client Applet
Client Applet
13
Network Architecture

• Limitations
• Object server is a single point of failure
• Communication bottleneck
• Not scalable
• Linear relationship between the number of clients
  and the network resources required to broadcast a
  message
• (Communication Protocol)

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Communication Protocol

• Synchronization messages
• Create, Delete, Lock, Unlock
• Transformation messages
• Translate, Rotate, Scale
• Session management
• Join - New client joins a session
• Leave - Client leaves a session

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Synchronization Messages

• Create and Delete
• Ensure that all clients are aware of the same
  objects
• Lock and Unlock
• Ensure mutual exclusive access by each client to
  each object
• Critical for maintaining a consistent shared
  model
• Must be delivered reliably

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Transformation Messages

• Notify other clients of object transformations
• Contain absolute transformation information
• Occur with greater frequency
• Are broadcast to all of the clients

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Transformation Messages

• Contain absolute transformation information
• Can tolerate unreliable message delivery
• It is possible to lose all but the last
  transformation message in a sequence and still
  have an object properly transformed

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Scalable Message Delivery

• Can use multicast communication to deliver
  transformation messages scalably
• Multicast can deliver a message to a group of
  receivers without sending a separate message for
  each receiver

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Multicast Communication
Object Database

• Transformation messages sent through multicast
  group

Object Server
Multicast Group
TCP/IP Socket
TCP/IP Socket
Multicast Socket
HTTP Server
HTTP Server
Proxy
Proxy
TCP/IP Socket
TCP/IP Socket
Browser
Browser
Client Applet
Client Applet
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System Limitations

• Object Server
• Centralized coordinator
• Single point of failure
• Communication bottleneck
• 3D Modeling Applets
• Latency of shadow objects
• Addressed with application level congestion
  control

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Future Work

• Combine Proxy and Client Applet
• Reliable Multicast
• Fully-distributed Object Server

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Combine Proxy and Client Applet

• Signed applet can connect to multicast group

Object Server
Multicast Group
TCP/IP Socket
Multicast Socket
Client
Client
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Reliable Multicast

• Provides scalable message delivery without
  sacrificing reliability
• Techniques for implementing reliable multicast
• SRM (Scalable Reliable Multicast)

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Fully-Distributed Object Server

• Eliminate the centralized coordinator
• Object locking handled by distributed mutual
  exclusion protocol

Client
Client
Multicast Socket
Reliable Multicast
Multicast Socket
Client
Client
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Future Applications

• Collaborative CAD
• Designing buildings
• Collaborative movie animation
• Creating movies
• Distance Learning
• Collaborative problem solving

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Conclusions

• Demonstrate a Web-based collaborative 3D modeling
  environment.
• Leverage emerging and existing Web-based
  technology for 3D modeling.
• Balance reliable and scalable communication using
  unicast and multicast sockets.
• Communication protocol that supports fine-grained
  synchronization, high-level of interactivity.

27
Demo

• www.cs.ucsb.edu/alex/c3d/index.html