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Input Devices: Trackers, Navigation and Gesture Interfaces

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Title: Input Devices: Trackers, Navigation and Gesture Interfaces


1
Input DevicesTrackers, Navigation and Gesture
Interfaces
2
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)
3

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
4

Input Devices
  • Trackers measure the motion of objects such as
    users
  • 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).
  • Vision-based trackers (new)

5

Input Devices
6

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 .

7

Input Devices
  • Tracker characteristics

8

Input Devices
  • Tracker characteristics

9

Input Devices
  • Tracker characteristics

Real object fixed position
10

Input Devices
  • Tracker characteristics

11

Input Devices
  • Tracker characteristics

Tracker Update Rate
12

Input Devices
  • Mechanical Trackers
  • Definition A mechanical tracker consists of a
    serial or
  • parallel kinematic structure composed of links
    interconnected
  • by sensorized joints.

13

Input Devices
  • Mechanical Trackers
  • Pros
  • Use sensors imbedded in exoskeletons to measure
    position
  • Have extremely low latencies
  • Are immune to interference from magnetic fields
    and large metal objects
  • Cons
  • But limit the users freedom of motion
  • Can be heavy is worn on the body

14

Input Devices
Push 1280 (Fakespace Inc)
15

Input Devices
Exoskeleton structure
Interface With computer
16

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

17

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

18

Input Devices
Magnetic tracker with the old Data Glove
19

Input Devices
Electronic interface
Source
Stylus
Receiver
Fastrack magnetic tracker system
20

Input Devices
Long Ranger source for the tracker system
Source
21

Receivers
Source
Input Devices
Fastrack magnetic tracker electronics
22
Polhemus Long Ranger tracking errors (Rutgers)
23
Tracking error as a function of tripod height
24
  • Liberty LATUS A Polhemus Wireless Tracker
  • Uses wireless sources, now called markers, each
    with a different frequency
  • Each source position is measured by a receptor
    within 8 ft (50 sq. ft). 1 receiver can track 4
    markers.
  • The system can have up to 12 markers and up to 16
    receptors
  • Sampling rate is 188 Hz up to 8 markers and
  • drops to 94 Hz from 9 to 12 markers
  • Markers are battery powered up to 2.5 hours and
    weigh 2 ounces each.
  • For one marker and one receptor accuracy is 0.04
    mm and 0.0012 degree at 1 ft range and drops
    afterwards.
  • Communication from base unit is RS232 or USB
  • Cost UP TO 64,000

25
  • PATRIOT A new Polhemus Wireless Tracker
  • Tracks up to four wireless sources (markers),
    each with a different frequency
  • Sampling rate is 50 Hz
  • Each source position is measured by a receiver
    receptor within 6 ft. One receiver can track up
    to 2 markers.
  • The system can have up to 2 receptors
  • Markers are battery powered up to 2 hours
  • Less performance than LATUS, but cheaper
    (14,000 instead of 60,000)


26
Input Devices
Motion Star wireless tracker (courtesy of
Ascension Technology)
27

Input Devices
DC Magnetic Tracker Block Diagram
28

Input Devices
Flock of Birds magnetic tracker (Ascension Co.)
29
Input Devices
Wireless suit (Ascension Technology)
Sensors 20/suit
100 updates/sec 3 meters range from base
unit Resolutionlt2 mm and lt.2 degrees
Electronic unit (2 hours battery life) 1.7 kg
(3.8 lb)
30

Input Devices
  • Two opposite ERTs 3.6?3.6 m
  • Two side-by-side ERTs 1.8 ?4.2 m
  • Readings weighted to the closer ERTs
  • Several Base Stations for several users

Motion Star block diagram
31

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.

32

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 ? (d
    metal-receiver)3

33

Input Devices
Magnetic tracker accuracy degradation
34

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

35

Input Devices
36

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.

37

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).

38

Input Devices
Ultrasonic tracker (Logitech)
39

Input Devices
Large-volume ultrasonic tracker (Logitech)
40

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

41

Input Devices
Optical trackers a) outside-looking-in b)
inside-looking-out
42

Input Devices
Outside-looking-in LaserBIRD optical tracker
43

Input Devices
Inside-looking-out LaserBIRD optical tracker
  • The two beams are offset
  • The three vertices are computed based on known
    offset, geometry and angular velocity of the
    beams
  • The average of the three vertices is computed and
    sent to the host at 240 sets/sec
  • Range is 2 ms latency smaller than that of
    magnetic trackers

44
  • Outside-looking in Vicon MX
  • Uses 4 Mpixel cameras with own 120 LED array
    (infrared, or visible red). Accuracy 0.02 of a
    pixel,
  • Camera has real-time onboard image processing
    (masking and thresholding)
  • Resolution 2352x1728 _at_ 160 fps
  • 8 cameras are connected to a MX net unit which
    then communicates with the PC

45

Input Devices
  • Outside-looking in Vicon MX
  • MX Link connects several MX Net units for more
    cameras
  • To interface with other devices like a force
    plate, sensing glove or eye tracker use a MX
    control unit.
  • User wears reflective markers (small spheres).

46

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).

47

HiBall 3100 wide area tracker
  • The sensor advantages are
  • High sampling rate (2000 Hz, 1000Hz for 2
    sensors, 500Hz for 4)
  • High accuracy (0.4 mm, 0.02) 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 (6 oz).

HiBall Optical Sensor
HiBall Optical Sensor interior
6 photodiodes
6 optical lenses
Signal conditioning electronics
(courtesy of 3rdTech Inc.)
48

HiBall 3000 tracker on an HMD
49

Types of VR Applications
Beacon array modules (6 strips with 8 LED/strip)
50

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.

51

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

52

Input Devices
IS 900 block diagram
VC 2.1- book CD
53
IS 900 software block diagram
54
Base unit
Sonic Strips
I-cube
Tracker components (InterSense Co.)
55
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 410 ms Max tracking area
900 meters2 (300 strips, 24 hubs)
Tracker components (courtesy of Intersense Co.)
56
I-Cube Accel./gyro
Ultrasonic emitter
InterSense Stereo Glasses tracker (courtesy of
Intersense Co.)
57
Accelerometer
Ultrasonic emitter
InterSense Stereo stylus tracker (courtesy of
Intersense Co.)
58

Input Devices
59
  • Hybrid Vision/Inertial Tracker
  • 6 DOF, accuracy 3 mm, 0.1 degree,
  • Latency 2 ms
  • Requires a minimum of 1 fiducial
  • for every 2 m2 at 2 m from camera
  • Update rate 120 Hz

IS 1200
InertiaCAM Fixed-focus lens, on-board DSP Weight
35 grams Tracking range 10 m per 10 cm of
fiducial diameter
Fiducials
60

Input Devices
  • Navigation and Gesture Input Devices
  • Navigation interfaces allow relative
  • position control of virtual objects
  • (including a virtual camera)
  • Gesture interfaces allow dextrous
  • control of virtual objects and interaction
  • through gesture recognition.

61

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.

62
Input Devices
VC 2.2 book CD
The Cubic Mouse
63
Input Devices
Trackballs
64
Input Devices
The Microscribe (Immersion Co.)
65

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 users hand.

66
Input Devices
Finger Degrees of Freedom
67
Input Devices
Hand work envelope vs. interface type
68
The Pinch Glove (Fakespace Co.) - no joint
measures, but contact detection
69
The Pinch Glove (Fakespace Co.)
70
5DT Data Glove
One optical fiber/finger
A)
5DT Data Glove Ultra
Roll/pitch sensing
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)
newer design
71
5DT Data Glove - continued
Two sensors/finger plus abduction sensors
Two gloves use one Bluetooth 2.4 GHz transmitter
on the users belt
The glove interface a) 14-sensor version b)
wireless kit
72
5DT Data Glove
73
5DT Data Glove
Glove has less sensors than hand joints Needs
to infer distal joint flexion angle
The coupling of intermediate and distal finger
joints
74
Input Devices
5DT Data Glove
75
Input Devices
5DT Data Glove
Linear calibration method
76

The DG5 glove
  • Uses one flex sensor/finger
  • Angles are obtained by measuring voltages
  • 100 gestures/sec
  • Sensor resolution 10 bit (1024 points),
  • cannot measure individual joints
  • Needs calibration
  • less expensive (about 495)

77

The new DG5 VHand glove 2.0
  • Uses one bend flex sensor/finger accelerometers
    for position/orientation
  • Angles are obtained by measuring voltages
  • 25 gestures/sec
  • Sensor resolution 10 bit (1024 points),
  • USB or wireless connection
  • Incorporates roll, pitch, tracking, 0.5 degree
    resolution
  • Needs calibration
  • less expensive (585 wired 785 wireless)
    www.dg-tech.it

78
The CyberGlove
  • Uses 18-22 linear sensors electrical strain
    gauges
  • Angles are obtained by measuring voltages on
  • a Wheatstone 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)

79
The CyberGlove (Vertex Co.)
VC 2.3 on book CD
80
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