A Lightweight ComputerVisionbased Electronic Travel Aid - PowerPoint PPT Presentation
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A Lightweight ComputerVisionbased Electronic Travel Aid
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Spatial audio. possibly interferes with user's auditory feedback from the world ... Spatial resolution is poor. Interesting spatial summation properties ... – PowerPoint PPT presentation
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Title: A Lightweight ComputerVisionbased Electronic Travel Aid
1
A Lightweight Computer-Vision-based Electronic
Travel Aid
- Andrew B. Raij (raij_at_cs.unc.edu)
- Enabling Tech Project Final Report
- 4/17/2003
Department of Computer Science, UNC-Chapel Hill
2
Long-term Goals
- Design and build a wearable, inconspicuous device
that assists people with visual disabilities with
orientation and mobility (OM) - Gathers info from the environment with one or
more cameras and presents the data to the user in
a useful form - Focus on gathering depth info this semester
- Explore useful ways to present depth to user
3
Previous ETAs (1)
- Cane
- A depth and acoustics probe for nearby things
- No long distance probing
- No probing up high
- Requires scanning back and forth across world
4
Previous ETAs (2)
- NavBelt
- Spatial audio
- possibly interferes with users auditory feedback
from the world - Uses sonars to build a local, 2D, birds-eye map
- Vertical resolution of depth is poor
- Modes
- Guidance Mode guides users around obstacles,
but requires dead-reckoning - Image Mode scans across map, increases pitch
and volume as depth decreases. Too much info,
requires lots of training
5
Previous ETAs (3)
- GuideCane
- Cane attached to robot that turns at obstacles
but maintains users desired course - Guidance tech based on NavBelt Guidance Mode
- Very intuitive, natural force feedback
- Restricted to relatively flat surfaces
- How does the user feel about being led by a
robot? Control issues? - Concerns about appearing different?
6
Previous ETAs (4)
- vOICe (http//www.seeingwithsound.com)
- Scans across images (like the NavBelt image mode)
and translates images to different sound cues. - Uses images - Inherently good vertical and
horizontal resolution, scans world for user - Auditory feedback could be lots of information to
deal with at once - Can require lots of time practicing to get used
to it - Some users claim it almost makes them feel like
they are seeing - Can also work with depth images
7
Depth Extraction
- We want to determine X given the two views
- First find the fundamental matrix F ?
xFx 0 - Use the fundamental matrix to find the projection
matrices P and P for C and C
- Use least-squares linear triangulation method to
calculate X fast - This method is more prone to errors from noise
8
Estimating F
- Estimating the fundamental matrix F
- 7 or more corresponding points
- Insert known points in scene
- Structured light
- Checkerboard
- robust searching for corresponding points in 2
views - possible, but not at every frame
- Need a scene with good features
- if geometric relationship between views is
constant, so is F, P, P - Only need to estimate F, P, P once, or maybe
just every once in a while
9
Depth Sampling
- At every frame we need to
- choose points to sample for depth
- All
- can be fast if epipolar lines are parallel to
scanlines - Edges and surrounding areas?
- Object extraction?
- Correspond them in 2 views
- Points that do not correspond well in both images
are not processed further
10
Spatial Perception (Ungar)
- Near-Space (Haptic) vs. Far-Space (Locomotor)
- Both spaces directly connected through vision
- Early and congenitally blind generally code the
world in terms of their own bodies, i.e.
near-space - Spatial relationships are understood but spatial
inference, rotation can be difficult - Recent research suggests people who are blind
tend to not learn/use strategies for
understanding locomotor space and its connection
to haptic space - Hypothesis tactile maps can bridge the gap
between locomotor and haptic space
11
Tactile Display
- Convey information through touch
- Two kinds of tactile displays I read about
- Vibration
- Thermal
- Others
- Pin Arrays
- Electric
12
Vibration
- Vibration for phones, PDAs, other small form
factor devices - Phone
- Ambient Touch
- Tactile Virtual Buttons
- Gloves, vests with piezo-electric buzzers
- Lots of others
13
Thermal
- Not enough work here
- Mostly for VE research
- blowing hot air on skin
- Thermal Phantom, Gloves
- Peltier cell, water-cooled heat sink
- Temperature Perception
- Spatial resolution is poor
- Interesting spatial summation properties
- Slow temp changes not very noticeable but fast
changes are - Body adapts to temperature change over time
- Unlikely to perceive clearly several areas on
body changing temp - Safety issues!
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