Input Devices: Trackers, Navigation and Gesture Interfaces

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Input DevicesTrackers, Navigation and Gesture
Interfaces
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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)
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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
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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)

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Input Devices
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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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Input Devices

• Tracker characteristics

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Input Devices

• Tracker characteristics

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Input Devices

• Tracker characteristics

Real object fixed position
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Input Devices

• Tracker characteristics

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Input Devices

• Tracker characteristics

Tracker Update Rate
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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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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

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Input Devices
Push 1280 (Fakespace Inc)
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Input Devices
Exoskeleton structure
Interface With computer
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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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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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Input Devices
Magnetic tracker with the old Data Glove
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Input Devices
Electronic interface
Source
Stylus
Receiver
Fastrack magnetic tracker system
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Input Devices
Long Ranger source for the tracker system
Source
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Receivers
Source
Input Devices
Fastrack magnetic tracker electronics
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Polhemus Long Ranger tracking errors (Rutgers)
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Tracking error as a function of tripod height
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• 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

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• 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)

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Input Devices
Motion Star wireless tracker (courtesy of
Ascension Technology)
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Input Devices
DC Magnetic Tracker Block Diagram
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Input Devices
Flock of Birds magnetic tracker (Ascension Co.)
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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)
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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
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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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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

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Input Devices
Magnetic tracker accuracy degradation
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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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Input Devices
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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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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
Outside-looking-in LaserBIRD optical tracker
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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

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• 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

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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).

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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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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.)
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HiBall 3000 tracker on an HMD
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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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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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Input Devices
IS 900 block diagram
VC 2.1- book CD
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IS 900 software block diagram
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Base unit
Sonic Strips
I-cube
Tracker components (InterSense Co.)
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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.)
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I-Cube Accel./gyro
Ultrasonic emitter
InterSense Stereo Glasses tracker (courtesy of
Intersense Co.)
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Accelerometer
Ultrasonic emitter
InterSense Stereo stylus tracker (courtesy of
Intersense Co.)
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Input Devices
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• 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
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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.

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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
VC 2.2 book CD
The Cubic Mouse
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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 users hand.

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Input Devices
Finger Degrees of Freedom
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Input Devices
Hand work envelope vs. interface type
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The Pinch Glove (Fakespace Co.) - no joint
measures, but contact detection
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The Pinch Glove (Fakespace Co.)
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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
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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
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5DT Data Glove
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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
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Input Devices
5DT Data Glove
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Input Devices
5DT Data Glove
Linear calibration method
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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)

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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

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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)

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