1. Input Devices: Trackers, Navigation and Gesture Interfaces
Rutgers University - Virtual Reality Technology

2. Rutgers University - Virtual Reality Technology
Input Devices
What is Virtual Reality?
“A high-end user interface that involves real-time simulation and interaction through multiple sensorial channels.” (vision, sound, touch, smell, taste)
Rutgers University - Virtual Reality Technology

3. Rutgers University - Virtual Reality Technology
Input Devices
Virtual objects have 6 degrees
of freedom (D.O.Fs):
three translations;
three rotations.
3-D System of coordinates of a VR object
Rutgers University - Virtual Reality Technology

4. Rutgers University - Virtual Reality Technology
Input Devices
Trackers measure the motion of “objects” such as user’s
wrist or his head vs. a fixed system of coordinates.
Technologies to perform this task:
Magnetic trackers (prevalent);
Ultrasonic trackers (less used);
Mechanical trackers (special cases);
Inertial/ultrasonic trackers (new).
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5. Rutgers University - Virtual Reality Technology
Input Devices
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6. Rutgers University - Virtual Reality Technology
Input Devices
Tracker characteristics:
Measurement rate – Readings/sec;
Sensing latency;
Sensor noise and drift;
Measurement accuracy (errors);
Measurement repeatability;
Tethered or wireless;
Work envelope;
Sensing degradation .
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7. Rutgers University - Virtual Reality Technology
Input Devices
Tracker characteristics:
Real object position
Accuracy
Resolution
Tracker position
measurements
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8. Rutgers University - Virtual Reality Technology
Input Devices
Tracker characteristics:
Real object fixed
position
Signal noise
Time
Tracker data
Rutgers University - Virtual Reality Technology

9. Rutgers University - Virtual Reality Technology
Input Devices
Tracker characteristics:
Sensor drift
Time
Tracker data
Real object fixed
position
Rutgers University - Virtual Reality Technology

10. Rutgers University - Virtual Reality Technology
Input Devices
Tracker characteristics:
Real object
position
Sensor latency
Time
Tracker data
Rutgers University - Virtual Reality Technology

11. Rutgers University - Virtual Reality Technology
Input Devices
Tracker characteristics:
Tracker Update Rate
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12. Rutgers University - Virtual Reality Technology
Input Devices
Mechanical Trackers
Definition: A mechanical tracker consists of a serial or
parallel kinematic structure composed of links interconnected
by sensorized joints.
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13. Rutgers University - Virtual Reality Technology
Input Devices
Mechanical Trackers
Use sensors imbedded in exoskeletons to measure position;
Have extremely low latencies;
Are immune to interference from magnetic fields;
But limit the user’s freedom of motion;
Can be heavy is worn on the body
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14. Rutgers University - Virtual Reality Technology
Input Devices
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15. Rutgers University - Virtual Reality Technology
Input Devices
Exoskeleton
structure
Interface
With
computer
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16. Rutgers University - Virtual Reality Technology
Input Devices
Magnetic Trackers
Definition: A magnetic tracker is a non-contact position
measurement device that uses a magnetic field produced
by a stationary TRANSMITTER to determine the real-time
position of a moving RECEIVER element
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17. Rutgers University - Virtual Reality Technology
Input Devices
Magnetic Trackers
Use low-frequency magnetic fields to measure position;
Fields are produced by a fixed source;
Size of source grows with the tracker work envelope;
The receiver is attached to the tracked object and
has three perpendicular antennas;
Distance is inferred from the voltages induced in the
antennas – needs calibration…
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18. Rutgers University - Virtual Reality Technology
Input Devices
Magnetic tracker with Data Glove
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19. Rutgers University - Virtual Reality Technology
Input Devices
Fastrack magnetic tracker system
Electronic interface
Source
Stylus
Receiver
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Input Devices
Long Ranger source for the tracker system
Source
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21. Rutgers University - Virtual Reality Technology
Receivers
Fastrack magnetic tracker electronics
Source
Input Devices
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22. Rutgers University - Virtual Reality Technology
Input Devices
Polhemus Long Ranger tracking errors (Rutgers)
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23. Rutgers University - Virtual Reality Technology
Tracking error as a function of tripod height
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24. Rutgers University - Virtual Reality Technology
Input Devices
DC Magnetic Tracker Block Diagram
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25. Rutgers University - Virtual Reality Technology
Input Devices
Flock of Birds magnetic tracker (Ascension Co.)
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26. Rutgers University - Virtual Reality Technology
Input Devices
Motion Star wireless tracker (courtesy of Ascension Technology)
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27. Rutgers University - Virtual Reality Technology
Input Devices
Wireless suit (Ascension Technology)
Sensors: 20/suit
100 updates/sec
3 meters range
from base unit
Resolution<2 mm
and <.2 degrees
Electronic unit
(2 hours battery life)
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28. Rutgers University - Virtual Reality Technology
Input Devices
Motion Star block diagram
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Input Devices
Magnetic Tracker Calibration
Use mechanical measurements to reduce errors;
Sensor noise – variation in measurement with no
real object motion – solved by over-sampling;
Size of errors grow from source outwards;
Errors both in position and orientation.
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30. Rutgers University - Virtual Reality Technology
Input Devices
Magnetic tracker accuracy degradation
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Input Devices
Magnetic Tracker Errors
due to ambient noise:
e ambient = Kn (d transmitter-receiver)4
due to metal:
Kr (d transmitter-receiver)4
e metal =
(d transmitter-metal)3 x (d metal-receiver)3
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32. Rutgers University - Virtual Reality Technology
Input Devices
Comparison of AC and DC magnetic trackers
DC trackers are immune to non-ferromagnetic metals
(brass, aluminum and stainless steel)
Both DC and AC trackers are affected by the presence of
Ferromagnetic metals (mild steel and ferrite).
Both are affected by copper;
AC trackers have better resolution and accuracy.
AC trackers have slightly shorter range
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33. Rutgers University - Virtual Reality Technology
Input Devices
Rutgers University - Virtual Reality Technology

34. Rutgers University - Virtual Reality Technology
Input Devices
Ultrasonic Trackers
Definition: A non-contact position measurement
device that uses an ultrasonic signal produced by a
stationary transmitter to determine the real-time
position/orientation of a moving receiver.
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35. Rutgers University - Virtual Reality Technology
Input Devices
Ultrasonic Trackers
Use low-frequency ultrasound to measure position;
Sound produced by a fixed triangular source (speakers);
Number of sources grows with the tracker work envelope;
The receiver is triangular and attached to the tracked
object and has three microphones;
Distance is inferred from the sound time of flight;
Sensitive to air temperature and other noise sources;
Requires “direct line of sight”;
Slower than magnetic trackers (max 50 updates/sec).
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Input Devices
Ultrasonic tracker (Logitech)
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Input Devices
Large-volume ultrasonic tracker (Logitech)
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Input Devices
Optical Trackers
Definition: A non-contact position measurement
device that uses optical sensing to determine the
real-time position/orientation of an object
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Input Devices
Optical trackers: a) outside-looking-in; b) inside-looking-out
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Input Devices
Inside-out optical tracker advantages
The best accuracy is close to the work envelope.
Very large tracking surface and resistance to visual occlusions (line of sight).
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Input Devices
Outside-looking-in
LaserBIRD optical tracker
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Input Devices
Inside-looking-out
LaserBIRD optical tracker
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43. Rutgers University - Virtual Reality Technology
HiBall 3000 wide area tracker
The sensor advantages are:
High sampling rate (2000 Hz);
High accuracy (0.5 mm, 0.03°) and high resolution (0.2 mm, 0.03°)
Impervious to metallic or ultrasonic interference;
Very large tracking area (up to 40 ft x 40 ft), small weight (8 oz).
HiBall Optical Sensor
HiBall Optical Sensor interior
6 photodiodes
6 optical lenses
Signal conditioning
electronics
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(courtesy of 3rdTech Inc.)

44. Rutgers University - Virtual Reality Technology
HiBall 3000 tracker
on an HMD
Lateral effect
photo diodes
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45. Rutgers University - Virtual Reality Technology
Types of VR Applications
Beacon array modules
(6 strips with 8 LED/strip)
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Input Devices
Hybrid Ultrasonic/Inertial Trackers
No interference from metallic objects;
No interference from magnetic fields;
Large-volume tracking;
“Source-less” orientation tracking;
Full-room tracking;
A newer technology.
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47. Rutgers University - Virtual Reality Technology
Input Devices
But…
Accelerometer errors a lead to decreased
accuracy since x= a t2 2
Errors grow geometrically in time!
Gyroscope errors compound position errors;
Needs independent position estimation to reduce
“drift”;
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48. Tracker components (InterSense Co.)
Base unit
Sonic Strips
I-cube
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49. Tracker components (courtesy of Intersense Co.)
Degrees of freedom: 6
Resolution: 1.5 mm RMS
Angular: 0.05o RMS
Update rate: 180 sets/s max
– one station
Down to 90 updates/sec
- for four stations.
Latency 4–10 ms
Max tracking area: 900 meters2
(300 strips, 24 hubs)
Tracker components (courtesy of Intersense Co.)
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50. Rutgers University - Virtual Reality Technology
I-Cube
Accel./gyro
Ultrasonic
emitter
InterSense Stereo Glasses tracker (courtesy of Intersense Co.)
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51. Rutgers University - Virtual Reality Technology
Accelerometer
Ultrasonic
emitter
InterSense Stereo stylus tracker (courtesy of Intersense Co.)
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52. Rutgers University - Virtual Reality Technology
Input Devices
IS 900 block diagram
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53. Rutgers University - Virtual Reality Technology
IS 900 software block diagram
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54. Rutgers University - Virtual Reality Technology
Link to VC 2.1 on book CD
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55. Rutgers University - Virtual Reality Technology
Input Devices
Rutgers University - Virtual Reality Technology

56. Rutgers University - Virtual Reality Technology
Input Devices
Navigation and Gesture Input Devices
Navigation interfaces allow relative
position control of virtual objects;
Gesture interfaces allow dextrous
control of virtual objects and interaction
through gesture recognition.
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57. Rutgers University - Virtual Reality Technology
Input Devices
Navigation Input Devices
Are the Cubic Mouse, the trackball and the
3-D probe;
Perform relative position/velocity
control of virtual objects;
Allow “fly-by” application by controlling
a virtual camera.
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Input Devices
The Cubic Mouse
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59. Rutgers University - Virtual Reality Technology
Link to VC 2.2 on book CD
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Input Devices
Trackballs
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Input Devices
The Microscribe (Immersion Co.)
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Input Devices
Gesture Input Devices
Are sensing gloves such as:
- Fakespace “Pinch Glove”
- 5DT Data Glove;
- The DidjiGlove
- Immersion “CyberGlove”
Have larger work envelope than
trackballs/3-D probes;
Need calibration for user’s hand.
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63. Rutgers University - Virtual Reality Technology
Input Devices
Finger Degrees of Freedom
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Input Devices
Hand work envelope vs. interface type
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65. Rutgers University - Virtual Reality Technology
The Pinch Glove (Fakespace Co.)
- no joint measures, but contact detection
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66. Rutgers University - Virtual Reality Technology
The Pinch Glove (Fakespace Co.)
Rutgers University - Virtual Reality Technology

67. The glove interface: a) five-sensor version; b) 16-sensor version
5DT Data Glove
One optical fiber/finger A)
Roll/pitch sensing
Two sensors/finger plus
abduction sensors
100 datasets/sec, 12 bit A/D flexion resolution,
wireless version transmits data at 30 m, needs calibration
The glove interface: a) five-sensor version; b) 16-sensor version
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68. Rutgers University - Virtual Reality Technology
5DT Data Glove
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69. The coupling of intermediate and distal finger joints
Glove has less sensors
than hand joints …
Needs to infer distal
joint flexion angle
5DT Data Glove
The coupling of intermediate and distal finger joints
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Input Devices
5DT Data Glove
Rutgers University - Virtual Reality Technology

71. Linear calibration method
Input Devices
5DT Data Glove
Linear calibration method
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The Didgiglove
Inexpensive wired glove for computer animation;
Uses capacitive sensors (two per finger) and a 10-bit A/D converter (1,024 points);
Can do 70 hand configuration reads/sec.;
Communicates with the host over an RS232 (19.2 k)
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73. Rutgers University - Virtual Reality Technology
The CyberGlove
Uses linear sensors – electrical strain gauges;
Angles are obtained by measuring voltages on
a Wheastone bridge;
112 gestures/sec “filtered”.
Sensor resolution 0.5 degrees, but errors accumulate
to the fingertip (open kinematic chain);
Sensor repeatability 1 degree
Needs calibration when put on the hand;
Is expensive (about $10,000)
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The CyberGlove (Vertex Co.)
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Link to VC 2.3 on book CD
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