progressive transmission of appearance preserving octree-textures

Progressive Transmission ofAppearance Preserving Octree-

Textures

Camille Perin

Web3D 2008August 9, 2008

Julien Lacoste Bruno Jobard

LIUPPAUniversity of Pau

France

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• A realistic image synthesis involves a great complexity for the object’s geometry.

Motivations

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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.

Motivations

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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

Motivations

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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

Motivations

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69 000 faces69 000 faces 600 faces600 faces600 faces 600 faces

+ Normal Map+ Normal Map

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?

Motivations

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Proposition

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

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APO TextureOctree 1D encoding2D Texture Encoding

Network ArchitectureClient/Server architectureAppearance Data updatesData Transmission Control

Results

Talk Overview

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• 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

Octree 1D sorting

APO Construction

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

APO 2D Encoding

APO Construction

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• Simple HTTP web server, only holds the data– No computation during transfer and rendering

• The client viewer is a Java Applet using JOGL

Viewer Architecture

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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

Client Viewer

Viewer Architecture

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Results

Viewer Architecture

After 2s After 10s After 30s

• Demo:http://web.univ-pau.fr/~jlacoste/APOWebViewer/

demoApplet.html

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Finer details unnecessary → Data transfer stops

Data Transfer Control

Viewer Architecture

• Computes screen-size projection of finer node

• Stops when size is below one pixel

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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

Conclusion

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THANKS !Questions

Contact :julien.lacoste@univ-pau.fr

http://web.univ-pau.fr/~jlacoste