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 Motion parallax

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

Lighting model Lambertian, specular, ambient + cast shadows

Standard lighting model Specular refection diffuse reflection = lambertian Ambient illumination

Examples

Shading Specular reveals fine detail

Cushion Tree Map Jarke Van Wijk

Contour and Shading

Textures for surface orientation (Interrante)

Understanding surface shape Victoria Interrante

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

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

Occlusion: The strongest depth cue

Perspective

Perspective (Cockburn and McKenzie) Perspective Picture plane position Occlusion Picture plane position Occlusion

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

Structure from Motion

Cast Shadows

Stereo Vision Basics

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

Frame Cancellation

Relative Importance, 96 Cutting, 1996 Depth Contrast Depth (meters) Occlusion Relative size Height in field Binocular disparity Motion parallax Convergence accommodation Aerial

Task Based Space Perception The important cues depend on the task

Cue dependencies

Yes of course 3D can give us more But 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

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

Random Graphs

Glenn looking at a graph

Fish Tank VR

The task

Stereo +60% Motion +130% Stereo + Motion +200%

How to generate Motion? Passive rotation Hand coupled rotation Head-coupled rotation Time has does not vary much

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

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

Stereo Vision Basics

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

Cyclopean Scale: (with Cyril Gobrecht)

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

Virtual Eye Separation

Conclusion – 3D is better but only it adds something 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)

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

Stereo shutter glasses Alternate right and left eye images on monitor. Syncronized shutters block right and left eyes in alternation Monitor: 120 Hz R,L eyes 60 Hz each Problems: ghosting due to slow Phosphor decay. Lower resolution CRT displays only Expensive glasses

Polaroids R L Silver screen Preserves polarization Problems: ghosting Advantages: Cheap glasses

Anaglyphs Problems: Ghosting Inability to use color

Lenticular To Right Eye To Left Eye The display uses cylindrical Prisms in vertical columns Problems: reduced resolution, limited head position. Theoretical limits on resolution What is wrong with this picture? Works with LCD displays

Mirror stereoscope Advantages: no ghosting Retains full brightness Full spatiotemporal resolution possible Disadvantage: Fixed head position.

HMD stereoscope Different screens for each eye. A high image quality is possible, but not currently available

VR What is it? What is it for? Perception/interaction

Issue Resolution Ghosting Vergence-focus conflict Occlusion Crossed disparities

Immersion VR HMD + head tracking Data glove

Fish Tank VR Head tracking, stereo, touch

Desk Top VR Interactive 3D

CAVE Head tracking – stereo Resolution problems Light scattering problems Vergence focus problem for near object Occlusion problems for near objects

Data walls (near immersion) Stereo, no head tracking, wide screen

Immersadesk Head tracking, stereo

Augmented reality (Feiner) Add text+images to real world See through glasses Very sensitive to head tracking Occlusion problems

Change in Eye Separation with Depth