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

Rutgers University - Virtual Reality Technology

Input Devices:

Trackers, Navigation and Gesture Interfaces


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)

Input Devices


3-D System of coordinates of a VR object

Virtual objects have 6 degreesof freedom (D.O.Fs):-three translations;-three rotations.

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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Tracker characteristics: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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Real object position

Accuracy

Resolution

Tracker position measurements

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Real object fixedposition

Signal noise

Time

Tracker data

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Real object fixedposition

Sensor drift

Time

Tracker data

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Real object position

Sensor latency

Time

Tracker data

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Tracker characteristics:Tracker characteristics:Tracker Update Rate

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Mechanical TrackersMechanical Trackers

Definition: A mechanical tracker consists of a serial or parallel kinematic structure composed of links interconnectedby sensorized joints.

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Mechanical TrackersMechanical 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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Exoskeletonstructure Interface

Withcomputer

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Magnetic TrackersMagnetic Trackers

Definition: A magnetic tracker is a non-contact position measurement device that uses a magnetic field producedby a stationary TRANSMITTER to determine the real-time position of a moving RECEIVER element

Input Devices


Magnetic TrackersMagnetic 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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Magnetic tracker with Data GloveInput Devices


Fastrack magnetic tracker system

Stylus

Source

Receiver

Electronic interface

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Long Ranger source for the tracker system

Source

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Fastrack magnetic tracker electronics

Source

Receivers

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Polhemus Long Ranger tracking errors (Rutgers)Input Devices


Magnitude of Error Vector / Moving Tripod

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

0 10 20 30 40 50 60 70 80

Transmitter-Receiver Distance (inches)

Ma

gn

itu

de

of

Err

or

Ve

cto

r (i

nch

es)

Err (54)

Err (60)

Err (66)

Err (72)

Err (80)

Tracking error as a function of tripod height


DC Magnetic Tracker Block Diagram

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Flock of Birds magnetic tracker (Ascension Co.)

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Motion Star wireless tracker (courtesy of Ascension Technology)

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Wireless suit (Ascension Technology)Sensors: 20/suit

100 updates/sec3 meters rangefrom base unitResolution<2 mmand <.2 degrees

Electronic unit(2 hours battery life)

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Motion Star block diagram

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Magnetic Tracker CalibrationMagnetic 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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Magnetic tracker accuracy degradation

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Magnetic Tracker ErrorsMagnetic 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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Comparison of AC and DC magnetic trackersComparison 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 ofFerromagnetic 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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Ultrasonic TrackersUltrasonic 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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Ultrasonic TrackersUltrasonic 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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Ultrasonic tracker (Logitech)Input Devices


Large-volume ultrasonic tracker (Logitech)

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Optical TrackersOptical 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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Optical trackers: a) outside-looking-in; b) inside-looking-out

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Inside-out optical tracker advantagesInside-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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Outside-looking-in

LaserBIRD optical tracker

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Inside-looking-out

LaserBIRD optical tracker

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HiBall 3000 wide area trackerHiBall 3000 wide area tracker

(courtesy of 3rdTech Inc.)

6 optical lenses 6 optical lenses

HiBall Optical Sensor HiBall Optical Sensor HiBall Optical Sensor interior HiBall Optical Sensor interior

Signal conditioning Signal conditioning electronics electronics

6 photodiodes 6 photodiodes

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 3000 trackerHiBall 3000 tracker on an HMDon an HMD

Lateral effect photo diodes


Types of VR ApplicationsTypes of VR Applications

Beacon array modulesBeacon array modules(6 strips with 8 LED/strip)(6 strips with 8 LED/strip)


Hybrid Ultrasonic/Inertial TrackersHybrid 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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But…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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Tracker components (InterSense Co.) Base unit

Sonic Strips

I-cube


Tracker components (courtesy of Intersense Co.)

Degrees of freedom: 6Resolution: 1.5 mm RMSAngular: 0.05o RMSUpdate rate: 180 sets/s max – one stationDown to 90 updates/sec - for four stations.Latency 4–10 msMax tracking area: 900 meters2

(300 strips, 24 hubs)


InterSense Stereo Glasses tracker (courtesy of Intersense Co.)

I-CubeAccel./gyro

Ultrasonic emitter


InterSense Stereo stylus tracker (courtesy of Intersense Co.)

Accelerometer

Ultrasonicemitter


IS 900 block diagramIS 900 block diagram

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IS 900 software block diagramIS 900 software block diagram


Link to VC 2.1 on book CD


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Navigation and Gesture Input DevicesNavigation 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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Navigation Input DevicesNavigation 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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The Cubic Mouse

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Trackballs

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The Microscribe (Immersion Co.)

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Gesture Input DevicesGesture 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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Finger Degrees of FreedomInput Devices


Hand work envelope vs. interface type

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The Pinch Glove (Fakespace Co.) - no joint measures, but contact detection


The Pinch Glove (Fakespace Co.)


The glove interface: a) five-sensor version; b) 16-sensor version

A)

One optical fiber/finger

Roll/pitch sensing Two sensors/finger plus abduction sensors

5DT Data Glove

100 datasets/sec, 12 bit A/D flexion resolution, wireless version transmits data at 30 m, needs calibration


5DT Data Glove


The coupling of intermediate and distal finger joints

5DT Data GloveGlove has less sensors than hand joints …Needs to infer distal joint flexion angle


5DT Data GloveInput Devices


Linear calibration method

5DT Data GloveInput Devices


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)

The Didgiglove


The CyberGlove

Uses 18-22 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)


The CyberGlove (Vertex Co.)

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

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