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Computer Graphics Research at Virginia

Explore perceptually guided interactive rendering and model simplification for large-scale geometric datasets. Learn about level of detail control, innovative algorithms, and immersive display technologies. Discover practical solutions and challenges in perceptual rendering research at Virginia.

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Computer Graphics Research at Virginia

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  1. Computer Graphics Research at Virginia David Luebke Department of Computer Science

  2. Outline • My current research • Perceptually Driven Interactive Rendering • Perceptual level of detail control • Wacky new algorithms • Scanning Monticello • Graphics resources • Building an immersive display • Building a rendering cluster?

  3. Perceptual Rendering • Next few slides from a recent talk • Apologies to UVA vision group

  4. Perceptually Guided Interactive Rendering David Luebke University of Virginia

  5. Motivation:Stating The Obvious • Interactive rendering of large-scale geometric datasets is important • Scientific and medical visualization • Architectural and industrial CAD • Training (military and otherwise) • Entertainment

  6. Motivation:Model Size • Incredibly, 3-D models are getting bigger as fast as hardware is getting faster…

  7. Big Models:Submarine Torpedo Room 1994: 700,000 polygons Courtesy General Dynamics, Electric Boat Div.

  8. Big Models:Coal-fired Power Plant 1997: 13 million polygons (Anonymous)

  9. Big Models:Plant Ecosystem Simulation 1998: 16.7 million polygons Deussen et al: Realistic Modeling of Plant Ecosystems

  10. Big Models:Double Eagle Container Ship 2000: 82 million polygons Courtesy Newport News Shipbuilding

  11. Big Models:The Digital Michelangelo Project 2000 (David): 56 million polygons 2001 (St. Matthew): 372 million polygons Courtesy Digital Michelangelo Project

  12. (Part Of) The Solution:Level of Detail • Clearly, much of this geometry is redundant for a given view • The idea: simplify complex models by reducing the level of detail used for small, distant, or unimportant regions

  13. Traditional Level of DetailIn A Nutshell… • Create levels of detail (LODs) of objects: 249,924 polys 62,480 polys 7,809 polys 975 polys Courtesy Jon Cohen

  14. Traditional Level of DetailIn A Nutshell… • Distant objects use coarser LODs:

  15. The Big Question How should we evaluate and regulate the visual fidelity of our simplifications?

  16. Measuring Fidelity • Fidelity of a simplification to the original model is often measured geometrically: METRO by Visual Computing Group, CNR-Pisa

  17. Measuring Visual Fidelity • However… • The most important measure of fidelity is usually not geometric but perceptual: does the simplification look like the original? • Therefore: • We are developing a principled framework for LOD in interactive rendering, based on perceptual measures of visual fidelity

  18. Perceptually Guided LOD: Questions And Issues • Several interesting offshoots: • Imperceptible simplification • When can we claim simplification is undetectable? • Best-effort simplification • How best to spend a limited time/polygon budget? • Silhouette preservation • Silhouettes are important. How important? • Gaze-directed rendering • When can we exploit reduced visual acuity

  19. Related Work:Perceptually Guided Rendering • Lots of excellent research on perceptually guided rendering • But most work has focused on offlinerendering algorithms (e.g., path tracing) • Different time frame! • Seconds or minutes vs. milliseconds • Sophisticated metrics: • Visual masking, background adaptation, etc…

  20. 8 7 8 Fold A A 2 10 10 6 6 9 9 3 3 Unfold 1 4 5 4 5 Perceptually Guided LOD: Our Approach • Approach: test folds (local simplification operations) against a perceptual model to determine if they would be perceptible

  21. Perception 101:The Contrast Sensitivity Function • Perceptual scientists have long used contrast gratings to measure limits of vision: • Bars of sinusoidally varying intensity • Can vary: • Contrast • Spatial frequency • Eccentricity • Velocity • Etc…

  22. Perception 101: The Contrast Sensitivity Function • Contrast grating tests produce a contrast sensitivity function • Threshold contrastvs. spatial frequency • CSF predicts the minimum detectablestatic stimuli

  23. Your Personal CSF Campbell-Robson Chart by Izumi Ohzawa

  24. Framework: View-Dependent Simplification • Next: need a framework for simplification • We use view-dependent simplification for LOD management • Traditional LOD: create several discrete LODs in a preprocess, pick one at run time • View-dependent LOD: create data structure in preprocess, extract an LOD for the given view

  25. View-Dependent LOD: Examples • Show nearby portions of object at higher resolution than distant portions View from eyepoint Birds-eye view

  26. View-Dependent LOD: Examples • Show silhouette regions of object at higher resolution than interior regions

  27. View-Dependent LOD: Examples • Show more detail where the user is looking than in their peripheral vision: 34,321 triangles

  28. View-Dependent LOD: Examples • Show more detail where the user is looking than in their peripheral vision: 11,726 triangles

  29. View-Dependent LOD:Implementation • We use VDSlib, our public-domain library for view-dependent simplification • Briefly, VDSlib uses a big data structure called the vertex tree • Hierarchical clustering of model vertices • Updated each frame for current simplification

  30. Folding a node affects a limited region: Some triangles change shape upon folding Some triangles disappear completely The Vertex Tree:Region Of Effect 8 7 8 Fold Node A A 2 10 10 6 6 9 9 3 3 UnfoldNode A 1 4 5 4 5

  31. I am interested in exploring new perceptually-driven rendering algorithms Don’t necessarily fit constraints of today’s hardware Ex: frameless rendering Ex: I/O differencing (time permitting) Give the demo, show the movie… Wacky New Algorithms

  32. Non-Photorealistic Rendering (time permitting) • Fancy name, simple idea: Make computer graphics that don’t look like computer graphics

  33. Non-Photorealistic Rendering • Fancy name, simple idea: Make computer graphics that don’t look like computer graphics

  34. Non-Photorealistic Rendering • Fancy name, simple idea: Make computer graphics that don’t look like computer graphics

  35. NPRlib • NPRlib: flexible callback-driven NP rendering Bunny: Traditional CG Rendering

  36. Non-Photorealistic Rendering • NPRlib: flexible callback-driven NP rendering Bunny: Pencil-Sketch Rendering

  37. Non-Photorealistic Rendering • NPRlib: flexible callback-driven NP rendering Bunny: Charcoal Smudge Rendering

  38. Non-Photorealistic Rendering • NPRlib: flexible callback-driven NP rendering Bunny: Two-Tone Rendering

  39. Non-Photorealistic Rendering • NPRlib: flexible callback-driven NP rendering Bunny: Two-Tone Rendering

  40. Scanning Monticello • Fairly new technology: scanning the world

  41. Scanning Monticello • Want a flagship project to showcase this • Idea: scan Thomas Jefferson’s Monticello • Historic preservation • Virtual tours • Archeological and architectural research, documentation, and dissemination • Great driving problem for scanning & rendering research • Results from first pilot project. • Show some data…

  42. Scanning Monticello

  43. Scanning Monticello

  44. Graphics Resources • 2 SGI Octanes • Midrange graphics hardware • SGI InfiniteReality2 • 2 x 225 MHz R10K, 1 Gb, 4 Mb cache • High-end graphics hardware: 13 million triangles/sec, 64 Mb texture memory • Hot new PC platforms (P3s and P4s) • High-end cards built on nVidia’s best chipsets • Stereo glasses, digital video card, miniDV stuff • Quad Xeon on loan • Software! • Maya, Renderman, Lightscape, Multigen, etc.

  45. Graphics Resources • Building an immersive display • NSF grant to build a state-of-the-art immersive display: • 6 projectors, 3 screens, passive stereo • High-end wide-area head tracker • 8 channel spatial audio • PCs to drive it all • Need some help building it…

  46. Graphics Resources • Building a rendering cluster? • Trying to get money to build a high-end rendering cluster for wacky algorithms • 12 dual-Xeon PCs: • 1 Gb RAM • 72 Gb striped RAID • nVidia GeForce3 • Gigabit interconnect • Don’t have the money yet, but do have 6 hot Athlon machines

  47. More Information • I only take students who’ve worked with or impressed me somehow • Summer work: best • Semester work: fine, but harder • Interested in graphics? • Graphics Lunch: Fridays @ noon, OLS 228E • An informal seminar/look at cool graphics papers • Everyone welcome, bring your own lunch

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