ucla engineering computer science indoor localization and navigation of wheelchair users with...
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UCLA ENGINEERING Computer Science
Indoor Localization and Navigation of Wheelchair Users with Smartphones
Ruolin Fan, Silas Lam, Emanuel Lin, Oleksandr Artemenkoⱡ, Mario GerlaUniversity of California, Los Angeles (UCLA)
{ruolinfan, silaslam, emanuel, gerla}@cs.ucla.eduⱡIlmenau University of Technology
oleksandr.artemenko@tu-ilmenau.de
UCLA ENGINEERING Computer Science
Outline
• Introduction• Background• System Design• Implementation• Evaluation• Conclusion
UCLA ENGINEERING Computer Science
Introduction
• GPS does not work indoors• Lack of satellite signals
• Need an alternative way to position ourselves indoors
• Try to utilize unique features pertaining to wheelchairs• Transform measured wheel rotations into both
distance and angular displacement• Crowd sourcing popular wheelchair access paths• Useful for blind/impaired wheelchair riders
UCLA ENGINEERING Computer Science
Background: Indoor Localization
• Triangulation methods from cellular, WiFi, or acoustic (Signal strength or signature)• Require landmark placement knowledge, previous
mapping of the site; affected by obstacles• Dead reckoning • Compute the current position based on a
previously known position and incremental displacement
• Can complement and rescue GPS and triangulation methods (eg Autogait[Percom 10])
UCLA ENGINEERING Computer Science
Wheelchair Dead Reckoning - Overview
• Get initial position of the wheelchair via GPS coordinates or other means
• Mark the wheels on the wheelchair at each spoke• Track the wheelchair’s movements by counting
rotations of the wheels using the marks (a “tick”)• Simple model (perfect traction, no sliding):• If wheels rotate at the same rate => straight
movement• If wheels rotate at different speeds => turns
UCLA ENGINEERING Computer Science
Inferring Movements
• Straight forward movement:• Both wheels move at the same rate• • cwheel: the wheel’s circumference• n: the number of marks on each wheel
• Sharp turns:• One wheel is moving while the other stays still• • • wchair: the width of the wheelchair
• cchairTurn: The circumference when the chair turns a full circle
• dtravelled: The distance travelled by the turning wheel
UCLA ENGINEERING Computer Science
Inferring Movements (Cont’d)
• General Turns• One wheel moves faster than the other• Derive equation using radians• , • And therefore• • In degrees,•
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Implementation
• Wheelchair Specifications• 8 magnets per wheel• 1 reed switch per wheel• Reed switches connected to
Bluetooth mouse• When magnet moves close
to reed switch, it trigger a mouse click event
UCLA ENGINEERING Computer Science
Implementation (Cont’d)
• Translate left/right mouse clicks to distance/direction traveled• Base calculations on physical wheelchair
measurements• Implemented straight movement and sharp turns
• Clicks detected by JavaScript in web browser• Events are sent via AJAX to PHP server and
MySQL database• Visualize wheelchair movement on a map
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Implementation Challenges
• Wheels are not always synchronized together• Magnets are far apart from one another• Result: coarse-grained data
• Wheels may “slip” due to physical imperfections
UCLA ENGINEERING Computer Science
Our Solution (can you explain better please??)
• Find ways to do “approximately equals”• Made our own low-pass filter in counting the
clicks• Single values that look like (1,0) would behave
like (1,1), and pairs like (1,0),(0,1) would also behave like (1,1)• Count small turns as straight movements until
confirmed to be a turn• When a turn is confirmed, backtrack the last
forward movement and aggregate the turn
UCLA ENGINEERING Computer Science
Example Forward+-----------+-------+-----------------+| time | state | magnitude |+-----------+-------+-----------------+| ... | ... | ... || 855742327 | F | 0.9106 || 855743328 | F/R | 1.13825 || 855744328 | F | 0.9106 || 855745328 | F | 0 || 855746327 | F/L | 1.13825 || 855747352 | F | 0.9106 || 855748332 | F/L | 1.13825 || 855749332 | F | 0.9106 |
UCLA ENGINEERING Computer Science
Example Turn+-----------+-------+-----------------+| time | state | magnitude |+-----------+-------+-----------------+| ... | ... | ... || 855713328 | F/L | 0.22765 || 855714328 | F | 0.22765 || 855715329 | L | 49.245283018868 || 855716329 | L | 24.622641509434 || 855723329 | L | 24.622641509434 || 855726328 | F | 0.68295 || 855727328 | F/L | 0.9106 |Total turn = 98.49 degrees
UCLA ENGINEERING Computer Science
Evaluation - General Movements
• Move the wheelchair around Boelter Hall 3rd floor, the main engineering building at UCLA
• Straight forward movement is accurate
• Turns are off• Only 8 magnets on a wheel:
can only measure degrees in increments of 24.5
• The closest to a 90 degree turn is 98 degrees
UCLA ENGINEERING Computer Science
Evaluation – Straight Movements
Error Rate vs. Travelling Speed
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Evaluation – Straight Movements (Cont’d)
Error Rate vs. Update Period (Fast Travelling Speeds)
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Improving Turn Accuracyassuming blue print is known
• Right angle correction• Assume 90 degree turns
when the turning angle is close to it
• Correction via boundary detection• Detect building
boundary and make corrections accordingly
Projected results Projected results
UCLA ENGINEERING Computer Science
Conclusions
• Indoor localization with a wheelchair can be accomplished by translating wheel rotation measurements into distance and direction
• Accuracy is high for slow to medium speeds, but decreases as speed goes up
• Improvements can be made by simply adding magnets
• Successful proof of concept project
UCLA ENGINEERING Computer Science
Future Work
• Improve the accuracy by exploiting existing smartphone sensors:• Compass, altimeter (in a multilevel building),
gyroscope, accelerometer• Synergize wheelchair dead reckoning with
WiFi signature methods• The wheelchair is used as surveyor, to calibrate
the signatures
UCLA ENGINEERING Computer Science
Thank You!
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