1. Distributed Handling of large Level of Detail Surfaces
Using binary triangle trees and progressive streaming.
Rune Aasgaard
Thomas Sevaldrud
SINTEF Applied Mathematics

2. Several ways to the goal
Centralized rendering, image distribution
Client-server terrain database

3. Which data where? Client terrain database Near graphics system
Some simple analysis functionality
Fast updates
Server terrain database
Huge!
Fast access
Updateable / re-generateable?

4. Level of Detail A coarse model retained for the whole domain
Use already transferred data
Refinement until required quality obtained
Coarsen when possible
Keep recently coarsened data in cache

5. Requirements Client terrain model
Closeness to graphics system
Triangle sets
3D coordinates
Texture coordinates
Normal vectors

6. Requirements Client terrain model
Simple analysis functionality
Connectivity
Single elevations
Profiles
Gradients

7. Requirements Client terrain model
Updates from server when:
Data becomes visible
More detail is required
Reduce to coarse level when:
Data becomes invisible
Less detail is required

8. Requirements Server terrain model
Huge!
Whole earth, 30” grid (DTED Level 0): points!
Whole earth, 3” grid (DTED Level 1): points!
Luckily, 2/3 of the earth is ocean
Major parts of the land is relatively flat

9. Requirements Server terrain model
Fast access, query expectations:
Grouped
Localized in area
Similar resolution level

10. Requirements Server terrain model
Model creation and editing, data sources
Variable quality
Variable density
Variable complexity
… integration…?

11. Selected solution - client
Binary triangle trees
Related to Lindström triangulations and ROAM algorithm
Simple algorithm for triangle fan creation
Simple relation between triangles and texture quads
Error sphere tree instead of priority queues

12. Binary Triangle Trees - refinement split

13. Binary Triangle Trees - forced neighbor split

14. Error sphere tree Acceptance radius based on Angular resolution
Triangle approximation error
Centered at triangle split point
May be common for triangle pair
Uses maximum radius
May contain child spheres
Also contains object radius

15. Error sphere tree

16. Selected solution - server
Quad trees
Easily transformable to BTT
Fast access system for disk based data
Simple algorithm for creation and updating with more detailed data

17. Server Quad tree

18. Selected solution - communication
Query
indexed on coordinates
collected as a query set
Reply
Elevations
Approximation errors