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

2. Interactive Visualization of Complex CAD Datasets2 MotivationMotivation 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 approach Challenge: Interactive visualization of a „Boeing 777“

3. Interactive Visualization of Complex CAD Datasets3 IntroductionIntroduction 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

4. Interactive Visualization of Complex CAD Datasets4 The „Boeing 777“ Model

5. Interactive Visualization of Complex CAD Datasets5 The „Boeing 777“ Model Geometric Complexity

6. Interactive Visualization of Complex CAD Datasets6 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

7. Interactive Visualization of Complex CAD Datasets7 Complex interwoven parts Self-intersecting polygons The „Boeing 777“ Model Complicated Topology

8. Interactive Visualization of Complex CAD Datasets8 The „Boeing 777“ Model Low Degree of Occlusion

9. Interactive Visualization of Complex CAD Datasets9 The „Boeing 777“ Model Same problem with most industrial CAD datasets Difficult for most large model rendering systems Detailed discussion in [Wald et al., EGSR 2004]

10. Interactive Visualization of Complex CAD Datasets10 The „Boeing 777“ Model Same problem with most industrial CAD datasets Difficult for most large model rendering systems Detailed 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)

11. Interactive Visualization of Complex CAD Datasets11 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() )

12. Interactive Visualization of Complex CAD Datasets12 Memory Management OS 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 availability Detect and prevent page faults using tile table

13. Interactive Visualization of Complex CAD Datasets13 Memory Management Tile Table Simple hash table to efficiently check tile availability 1 tile = 16 pages

14. Interactive Visualization of Complex CAD Datasets14 Memory Management Tile 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() )

15. Interactive Visualization of Complex CAD Datasets15 Proxy Objects Bridging 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

16. Interactive Visualization of Complex CAD Datasets16 Proxy Objects Structure 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

17. Interactive Visualization of Complex CAD Datasets17 Proxy Objects Structure When ray traversal has to be canceled –Interpolate shading information from closest ray directions

18. Interactive Visualization of Complex CAD Datasets18 Proxy Objects Results Immediately after system startup Without proxies (red: canceled rays)With proxies

19. Interactive Visualization of Complex CAD Datasets19 Proxy Objects Results After ~30 seconds (more than 2 GByte loaded) Without proxies (red: canceled rays)With proxies

20. Interactive Visualization of Complex CAD Datasets20 High-Quality Shading Shadows Without shadows and highlights

21. Interactive Visualization of Complex CAD Datasets21 High-Quality Shading Shadows Pixel-accurate shadows and highlights –Simple integration into a ray tracer –Significant improvement of depth perception

22. Interactive Visualization of Complex CAD Datasets22 High-Quality Shading Observer Light Source Difficult to place light sources Attach directional light to observer

23. Interactive Visualization of Complex CAD Datasets23 Results Video (640x480 pixels, up to 3 fps)

24. Interactive Visualization of Complex CAD Datasets24 SummarySummary 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

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