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Space Perception: the towards-away direction

Space Perception: the towards-away direction. Cost of Knowledge Depth Cues Tasks Navigation. Lets think about space as a cost of knowledge. Do these make any sense?. The perception for action pathway. Depth Cues. Shape from Shading - texture Occlusion Perspective Shadows Stereo

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Space Perception: the towards-away direction

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  1. Space Perception: the towards-away direction • Cost of Knowledge • Depth Cues • Tasks • Navigation

  2. Lets think about space as a costof knowledge.

  3. Do these make any sense?

  4. The perception for action pathway

  5. Depth Cues • Shape from Shading - texture • Occlusion • Perspective • Shadows • Stereo • Motion parallax

  6. Perception of surface shape • Simple lighting model • Light from above and at infinity • Specular, Diffuse and Ambient components • Oriented texture can enhance shape perception

  7. Lighting model Lambertian, specular, ambient + cast shadows

  8. Standard lighting model Ambient illumination Specular refection diffuse reflection = lambertian

  9. Examples

  10. Shading Specular reveals fine detail

  11. Cushion Tree Map Jarke Van Wijk

  12. Contour and Shading

  13. Textures for surface orientation (Interrante)

  14. Understanding surface shape Victoria Interrante

  15. Lighting • Simple lighting model • Not photorealistic • Single light source from above and at infinity • Specular for detail • Cast shadows if scene is simple

  16. The 3D vs 2D debate • Should we display abstract data in 3D? • Depth cue theory • Depth cues are environmental information that tell us about space • Can be applied somewhat independently

  17. Occlusion: The strongest depth cue

  18. Perspective

  19. Perspective

  20. Perspective (Cockburn andMcKenzie) Perspective Picture plane position Occlusion Picture plane position Occlusion

  21. Atmospheric perspective “depth cueing” in CG Reduce contrast with distance

  22. Structure from Motion

  23. Cast Shadows

  24. Stereo Vision Basics

  25. Stereopsis • Based on disparities • A super acuity • Only good near point of fixation • Poor for large differences • Double imaging possible for 1/10th deg.

  26. Frame Cancellation

  27. Relative Importance , 96 Motion parallax 0.001 Occlusion Height in field 0.01 Relative size Depth Contrast 0.1 Binocular disparity Convergence accommodation 1.0 Aerial 1 10 100 Depth (meters) Cutting, 1996

  28. Task Based Space Perception The important cues depend on the task

  29. Cue dependencies

  30. Yes of course 3D can give us moreBut only if it supports some task • Locomotion • Heading, occlusion • Understanding the shape of surfaces • Shading, texture, stereo, motion • Tracing paths in graphs • motion stereo • Local reaching • stereo – convergence

  31. Relative position • For fine judgments - threading a needle stereo is important +shadows, occlusion • For large scale judgments, perspective, motion parallax, linear perspective are all important. Stereo is not important

  32. Random Graphs

  33. Glenn looking at a graph

  34. Fish Tank VR

  35. The task

  36. Stereo +60% Motion +130% Stereo + Motion +200%

  37. How to generateMotion? • Passive rotation • Hand coupled rotation • Head-coupled rotation • Time has does not vary much

  38. Surface shape perception (Norman Todd and Phillips) Note: Random textures on surfaces Stereo and motion roughly equal Note large angular error ~ 20 degrees Observation: Stereopsis is a super-acuity and relies on fine texture disparity gradients

  39. Stereo Display Requirements • 3D GIS data • Comfortable stereo display • Many orders of magnitude • Better than normal stereopsis

  40. Stereo Vision Basics

  41. We Know That • Vergence and focus conflict • Stereo perception is plastic (Wallack) • Can be rapidly recalibrated (Judge and Miles) • There is a synergy with motion parallax • Occlusion is a strong cue to depth

  42. Cyclopean Scale: (with Cyril Gobrecht)

  43. Cyclopean Scale Helps with • Vergence focus conflict • Diplopia • Disparity scaling • Frame cancellation • It works dynamically? • Change the virtual eye separation

  44. Virtual Eye Separation

  45. Space perception depends on the task Occlusion the most important depth cue – consider that windows rely on it Perspective may not add anything by itself Stereo important for close interaction Motion important for 3D layout Shape-from shading and texture important for surface perception (but non photorealist) Conclusion – 3D is better but only it adds something

  46. Stereo technologies • Frame-sequential (shutter glasses) • Polaroids • Mirror stereoscope • HMDs • Color anaglyphs • Chromadepth • Holograms

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