Progressive Transmission of Appearance Preserving Octree-Textures

1
Progressive Transmission ofAppearance Preserving
Octree-Textures
Web3D 2008 August 9, 2008
Camille Perin
Julien Lacoste
Bruno Jobard
LIUPPA University of Pau France
2
Motivations

• A realistic image synthesis involves a great
  complexity for the objects geometry.

3
Motivations

• On a distributed visualization system, the
  transmission of the full geometry takes too much
  time.
• To avoid waiting time, use LOD representation of
  the geometry.
• First a light low resolution model is transmitted
  
• Higher resolution meshes are downloaded while
  interacting with low resolution object.

4
Motivations

• Problem with LOD representation
• The server holds several models
• Each version is fully transmitted the amount of
  data to transfer is increased
• Popping effect on the transition between two
  levels
• To avoid these problems
• progressive representation of meshes

5
Motivations

• Progressive Meshes (Hoppe, 96)
• Low Resolution Mesh vertex split operations
• No popping effect, smooth transition
• Download according to viewpoint
• A major problem remains
• Hard to render a complex geometry
• Distributed network memory constraints

6
Motivations

• For realtime rendering, the complexity can be
  encoded in a normal map, thus reducing the number
  of polygons.
• How to tramsit efficiently only the appearance?

600 faces Normal Map
69 000 faces
600 faces
7
Proposition

• Use the Appearance Preserving Octree-Texture
  (APO)
• Octree-Texture encoding the normal map
• Allows realtime rendering
• Hierarchical representation ? LOD Transmission

8
Talk Overview
APO Texture Octree 1D encoding 2D Texture
Encoding Network Architecture Client/Server
architecture Appearance Data updates Data
Transmission Control Results
9
APO Construction
Octree 1D sorting

• The octree is breadth first sorted in a 1D array
• Each node has a pointer toward its first child
• Root is at index 0, the coarser levels are the
  first ones in the array
• Internal nodes contain an averaged normal
• Inner mip-mapping of the texture

10
APO Construction
APO 2D Encoding

• Conversion from 1D array to 2D texture
• Top texels coarser levels
• Bottom texels finer levels

11
Viewer Architecture

• Simple HTTP web server, only holds the data
• No computation during transfer and rendering
• The client viewer is a Java Applet using JOGL

12
Viewer Architecture
Client Viewer

• Client downloads
• the simplified mesh (light)
• the APO while rendering
• Each time the buffer is full / Each time step
• Data sent to GPU to update APO (glTexSubImage)
• Buffer cleared client remains light in memory

13
Viewer Architecture
Results
After 30s
After 2s
After 10s

• Demo
• http//web.univ-pau.fr/jlacoste/APOWebViewer/demo
  Applet.html

14
Viewer Architecture
Data Transfer Control

• Finer details unnecessary ? Data transfer stops

• Computes screen-size projection of finer node
• Stops when size is below one pixel

15
Conclusion

• Progressive transmission of Appearance
• Nearly immediate interaction with low resolution
  version of objects
• Details appear smoothly
• Manipulation of high detailed objects
• No software installation
• Viewer is a browser applet
• Data privacy
• Only low resolution meshes are transmitted

16
THANKS !Questions
Contact julien.lacoste_at_univ-pau.fr http//web.un
iv-pau.fr/jlacoste