Progressive Transmission of Appearance Preserving Octree-Textures Camille Perin Web3D 2008 August 9, 2008 Julien LacosteBruno Jobard LIUPPA University of Pau France

Julien Lacoste – Progressive Transmission of APO – Web 3D / 16 A realistic image synthesis involves a great complexity for the object’s geometry. Motivations

Julien Lacoste – Progressive Transmission of APO – Web 3D / 16 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

Julien Lacoste – Progressive Transmission of APO – Web 3D / 16 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

Julien Lacoste – Progressive Transmission of APO – Web 3D / 16 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

Julien Lacoste – Progressive Transmission of APO – Web 3D / faces 600 faces + 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

Julien Lacoste – Progressive Transmission of APO – Web 3D / 16 Proposition Use the Appearance Preserving Octree-Texture (APO) – Octree-Texture encoding the normal map – Allows realtime rendering – Hierarchical representation → LOD Transmission

Julien Lacoste – Progressive Transmission of APO – Web 3D / 16 APO Texture Octree 1D encoding 2D Texture Encoding Network Architecture Client/Server architecture Appearance Data updates Data Transmission Control Results Talk Overview

Julien Lacoste – Progressive Transmission of APO – Web 3D / 16 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

Julien Lacoste – Progressive Transmission of APO – Web 3D / 16 Conversion from 1D array to 2D texture  Top texels: coarser levels  Bottom texels: finer levels APO 2D Encoding APO Construction

Julien Lacoste – Progressive Transmission of APO – Web 3D / 16 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

Julien Lacoste – Progressive Transmission of APO – Web 3D / 16 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

Julien Lacoste – Progressive Transmission of APO – Web 3D / 16 Results Viewer Architecture After 2sAfter 10s After 30s Demo:

Julien Lacoste – Progressive Transmission of APO – Web 3D / 16 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

Julien Lacoste – Progressive Transmission of APO – Web 3D / 16 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

Julien Lacoste – Progressive Transmission of APO – Web 3D / 16 THANKS ! Questions Contact :