Interactive Visualization of Exceptionally Complex Industrial CAD Datasets

1. Interactive Visualization of Exceptionally Complex IndustrialCAD Datasets Andreas Dietrich Ingo Wald Philipp Slusallek Computer Graphics Group Saarland University http://graphics.cs.uni-sb.de

2. Motivation • CG hardware performance has dramatically increased • Typically based on rasterization technology • Can render many million triangles / second • Scene complexity rises even faster • Many CAD datasets too complex to be displayed interactively • Rasterization algorithms too limited • Real-Time Ray Tracing approachChallenge: Interactive visualization of a „Boeing 777“ Interactive Visualization of Complex CAD Datasets

3. Introduction • Virtual prototyping becoming increasingly important • Collaborative engineering • CAD design of complete aircrafts, ships, buildings, etc. • Many independent teams design individual components • Millions of single parts modeled with full geometric detail • Complete datasets become extremely large • Goal: Direct interactive display of original CAD data Interactive Visualization of Complex CAD Datasets

4. The „Boeing 777“ Model Interactive Visualization of Complex CAD Datasets

5. The „Boeing 777“ ModelGeometric Complexity Interactive Visualization of Complex CAD Datasets

6. The „Boeing 777“ Model • More than 350 million individual triangles • 12 GByte raw model data • Complicated topological structure • Low degree of occlusion • „Soup“ of unconnected polygons Interactive Visualization of Complex CAD Datasets

7. The „Boeing 777“ ModelComplicated Topology Complex interwoven parts Self-intersecting polygons Interactive Visualization of Complex CAD Datasets

8. The „Boeing 777“ ModelLow Degree of Occlusion Interactive Visualization of Complex CAD Datasets

9. The „Boeing 777“ Model • Same problem with most industrial CAD datasets • Difficult for most large model rendering systemsDetailed discussion in [Wald et al., EGSR 2004] Interactive Visualization of Complex CAD Datasets

10. The „Boeing 777“ Model • Same problem with most industrial CAD datasets • Difficult for most large model rendering systemsDetailed discussion in [Wald et al., EGSR 2004] • Real-Time Ray Tracing approach Goal: Interactive visualization on a single PC (Dual AMD Opteron 1.8 GHz, 6 GByte RAM) Interactive Visualization of Complex CAD Datasets

11. Out-of-Core Ray Tracing • Ray tracing capable of handling massive models • Logarithmic in the number of triangles • Multi-level Kd-trees as hierarchical spatial index • „Boeing 777“ model requires 30 – 40 GByte on disk • Out-of-core mechanism needed • Build index structures offline on disk • Map disk data into 64-bit address space (mmap()) Interactive Visualization of Complex CAD Datasets

12. Memory ManagementOS Based Memory Mapping • Advantages of OS based memory mapping • Automatic demand paging • Address translation and I/O handled by CPU and OS • Fine cache granularity (pagesize 4 KByte) • Problems • Access to unavailable data causes page faults • Stalling of rendering process inhibits interactivity • Manually check data availabilityDetect and prevent page faults using tile table Interactive Visualization of Complex CAD Datasets

13. Memory ManagementTile Table • Simple hash table to efficiently check tile availability 1 tile = 16 pages Interactive Visualization of Complex CAD Datasets

14. Memory ManagementTile Handling • Tile descriptor • Bits 48 – 16 : Tile base address (detect hash collisions) • Bit 1 : Referenced bit • Bit 0 : Availability bit • Tiles loaded by asynchronous fetcher thread • Cache miss: Add tile ID to request queue • Asynchronous tile eviction • Free memory using „Second Chance“ algorithm (madvise()) Interactive Visualization of Complex CAD Datasets

15. Proxy ObjectsBridging Loading Time • Have to cancel ray traversal if data is not available • Large memory working set even for a single frame • All required data cannot be loaded every frame • Try to display some meaningful approximation • Memory resident „Proxy“ objects Replacement until exact data has been loaded Interactive Visualization of Complex CAD Datasets

16. Proxy ObjectsStructure • Proxies precomputed prior to rendering • Build proxy for subtrees accessed when crossing tile borders • Sample subtree volume with rays • Store normals and materials for set of discretized ray directions 28 directions / voxel : Less than 350 MByte for complete model Interactive Visualization of Complex CAD Datasets

17. Proxy ObjectsStructure • When ray traversal has to be canceled • Interpolate shading information from closest ray directions Interactive Visualization of Complex CAD Datasets

18. Proxy ObjectsResults • Immediately after system startup Without proxies (red: canceled rays) With proxies Interactive Visualization of Complex CAD Datasets

19. Proxy ObjectsResults • After ~30 seconds (more than 2 GByte loaded) Without proxies (red: canceled rays) With proxies Interactive Visualization of Complex CAD Datasets

20. High-Quality ShadingShadows • Without shadows and highlights Interactive Visualization of Complex CAD Datasets

21. High-Quality ShadingShadows • Pixel-accurate shadows and highlights • Simple integration into a ray tracer • Significant improvement of depth perception Interactive Visualization of Complex CAD Datasets

22. High-Quality ShadingObserver Light Source • Difficult to place light sources • Attach directional light to observer Interactive Visualization of Complex CAD Datasets

23. ResultsVideo (640x480 pixels, up to 3 fps) Interactive Visualization of Complex CAD Datasets

24. Summary • Out-of-core RT framework for complex models • Semi-manual OS based memory management system • Proxy objects as replacement for missing data • Full interactivity during progressive loading • Pixel-accurate shadows • Future work • Improve proxy quality • Sophisticated lighting simulation Interactive Visualization of Complex CAD Datasets

25. Questions ? For more information see http://graphics.cs.uni-sb.de http://www.openrt.de http://www.intrace.com Source 3D data provided by and used with permission of the Boeing Company