Space perception
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Space Perception. Depth Cues Tasks Shape-from-Shading. 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.

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Space Perception

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Space Perception

  • Depth Cues

  • Tasks

  • Shape-from-Shading


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

Ambient illumination

Specular refection

diffuse reflection =

lambertian


Examples


Shading

Specular reveals fine detail


Cushion Tree Map Jarke Van Wijk


Contour and Shading


Textures for surface orientation (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


Perspective (Cockburn andMcKenzie)

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 1/10th deg.


Frame Cancellation


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


Task Based Space Perception


3D options

Vergence

Focus

Motion

Parallax

Stereopsis

Shape-from

Shading or

Texture

Perspective

Occlusion


Cue dependencies


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


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 generateMotion?

  • Passive rotation

  • Hand coupled rotation

  • Head-coupled rotation

  • Time has does not vary much


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


Change in Eye Separation with Depth


Understanding surface shape

Victoria Interrante


Norman, Todd & 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


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


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

Silver screen

Preserves polarization

R

L

Problems:

ghosting

Advantages: Cheap glasses


Anaglyphs

Problems:

Ghosting

Inability to use color


Works with LCD displays

Lenticular

To Right Eye

To Left Eye

The display uses cylindrical

Prisms in vertical columns

What is wrong with this picture?

Problems: reduced resolution, limited head position.

Theoretical limits on resolution


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


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