space perception: the towards- away direction the third dimension depth cues tasks navigation cost...
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Space Perception: the towards-away direction
The third dimension Depth Cues Tasks Navigation Cost of Knowledge Interaction
Lets think about space as a costof knowledge.
The perception for action pathway
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
Do these make any sense?
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
ShadingSpecular reveals fine detail
Cushion Tree Map Jarke Van Wijk
Lighting
Simple lighting model Not photorealistic Single light source from above and at
infinity Specular for detail Cast shadows if scene is simple
Contour and Shading
Textures for surface orientation (Interrante)
Understanding surface shape
Victoria Interrante
Occlusion: The strongest depth cue
Perspective
Perspective
Perspective (Cockburn and McKenzie)
PerspectivePicture plane positionOcclusion
Picture plane position
Occlusion
Atmospheric perspective
Reduce contrast with distance
“depth cueing” in CG
Structure from Motion
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Cast Shadows
Stereo Vision Basics
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Right eyeScreen
Left eye
Panum's Fusional Area
disparity = -
Stereopsis
Based on disparities A super acuity Only good near point of fixation Poor for large differences Double imaging possible for 1/10th deg.
Frame Cancellation
Relative Importance
, 96
Cutting, 1996
Depth
Con
trast
Depth (meters)
Occlusion0.001
0.01
0.1
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Relative size
Height in field
Binoculardisparity
Motionparallax
Convergenceaccommodation
Aerial
Task Based Space Perception
a
Task Planningand Execution
3D CognitiveModelof Environment
C1
C2
C3
C4
CN
a
C1
C2
C3
C4
CN
Task Planningand Execution
The important cues depend on the task
Cue dependencies
Occlusion
Linear Perspective
StereoVergence Kinetic Depth
Texture gradients
Depth of focus
Yes of course 3D can give us moreBut only if it supports some task Locomotion
Heading, occlusion, pathways Understanding the shape of surfaces
Shading, texture, stereo, motion Tracing paths in graphs
motion stereo (not shading, not motion) Local reaching
stereo – convergence – sometimes cast shadows
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
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Number of Nodes
Stereo head coupled perspective
Stereo head coupled perspective2D
2DStereo perspectiveHead coupled perspective
Stereo +60%
Motion +130%
Stereo + Motion+200%
How to generateMotion?
Passive rotation Hand coupled rotation Head-coupled
rotation
Time has does not vary much
Ste
reo
pass
ive
Pas
sive
rot
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2D
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tive
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reo
hand
Hea
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reo
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reo0
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1012
8T
ime
(sec
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Han
d co
uple
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2D
Per
spec
tive
Ste
reo
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Err
ors
(%)
Ste
reo
pass
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reo
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Surface shape perception (Norman Todd and Phillips)
Note: Random textures on surfaces
Stereo and motion roughly equalNote large angular error ~ 20 degrees
Observation: Stereopsis is a super-acuity and relies on fine texture disparity gradients
L=lightingS=specularT = texture
Graham Sweet.
Stereo Display Requirements
3D GIS data Comfortable stereo display Many orders of magnitude Better than normal stereopsis
Stereo Vision Basics
aa
Right eyeScreen
Left eye
Panum's Fusional Area
disparity = -
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)
a
OriginalScaled
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 glassesAlternate right and left eye images on monitor. Syncronized shutters block right and left eyes in alternation
Monitor: 120 HzR,L eyes 60 Hz each
Problems: ghosting due to slowPhosphor decay.Lower resolutionCRT displays onlyExpensive glasses
Polaroids
R
L
Silver screenPreserves polarization
Problems:ghosting
Advantages: Cheap glasses
Anaglyphs
Problems:GhostingInability to use color
Lenticular
To Right EyeTo Left Eye
The display uses cylindricalPrisms 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 ghostingRetains full brightnessFull 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
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