Input Devices: Trackers, Navigation and Gesture Interfaces Input - - PowerPoint PPT Presentation

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 degrees

• f freedom (D.O.Fs):
• three translations;
• three rotations.

Input Devices

Passive input: events triggered by the system’s monitoring

• f the user

Active input: events are triggered specifically by the user

– Trackers – Navigation-object manipulation devices – Gesture recognition – Classical input devices – Special input devices & platforms – Speech, biosignals

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). Optical trackers Input Devices

Why use tracking

Render the correct view or sound Manipulate objects Control avatars Give symbolic commands through an

alphabet of predefined movements

Input Devices

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 . Input Devices

Tracker characteristics: accuracy, resolution Tracker characteristics: accuracy, resolution

Real object position

Accuracy Resolution

Tracker position measurements

Input Devices

Tracker characteristics: Tracker characteristics: jitter jitter

Real object fixed position

Signal noise

Time Tracker data

Input Devices

Tracker characteristics: Tracker characteristics: drift drift

Real object fixed position

Sensor drift

Time Tracker data

Input Devices

Tracker characteristics: Tracker characteristics: latency latency

Real object position

Sensor latency

Time Tracker data

Input Devices Considerable latency can lead to simulation sickness The total (system) latency is also of importance

Tracker characteristics: Tracker characteristics:

Tracker Update Rate

Input Devices

Mechanical Trackers Mechanical Trackers

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

Mechanical Trackers Mechanical Trackers

Use sensors embedded in exoskeletons to measure position; Forward kinematics Have extremely low latencies and low jitter; Are immune to interference from magnetic fields; No problems with occlusions. But limit the user’s freedom of motion; Motion interference from the tracker arms. Limited work envelope. Can be heavy if worn on the body Input Devices

Input Devices

Exoskeleton structure Interface With computer Input Devices Angles measured by conductive potentiomet ers

Magnetic Trackers 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 Input Devices

Magnetic Trackers Magnetic Trackers

Use low-frequency AC or DC magnetic fields to measure position; Fields are produced by a fixed source; Three orthogonal coils/antennas excited sequentially Size of source grows with the tracker work envelope; The receiver is attached to the tracked object and has three perpendicular antennas; Distance/orientation is inferred from the voltages induced in the antennas Nine voltages needs calibration… Input Devices

Polhemus Isotrack AC Magnetic tracker with Data Glove Input Devices

Fastrack magnetic tracker system Stylus Source Receiver Electronic interface Input Devices 120meas/sec 30meas/sec for 4 receivers due to multiplexing

Long Ranger source for the tracker system Source Input Devices

AC trackers induce eddy currents to other

metal objects which in turn produce small magnetic fields thus distorting the overall magnetic field.

Magnitude of Error Vector / Moving Tripod

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 10 20 30 40 50 60 70 80 Transmitter-Receiver Distance (inches) Magnitude of Error Vector (inches) Err (54) Err (60) Err (66) Err (72) Err (80) Tracking error as a function of distance from the floor and transmitter-receiver distance

Polhemus Long Ranger Input Devices

DC magnetic trackers

Emitter sends three orthogonal DC magnetic

pulses using three antennas, one at a time

Time delay between excitation of source and

sampling of receivers (eddy currents fade out)

Earth’s magnetic field is subtracted. Calibration is needed. Ascension: Flock of birds

– 144 measurements/sec regardless of the number

• f receivers (parallel sampling of each

receiver).

DC Magnetic Tracker Block Diagram Input Devices

Motion Star wireless tracker (courtesy of Ascension 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)

Input Devices

Magnetic tracker accuracy degradation Input Devices

Magnetic Tracker Errors 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 Input Devices

Comparison of AC and DC magnetic trackers 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 Input Devices

Input Devices

Ultrasonic Trackers 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.

Input Devices

Ultrasonic Trackers Ultrasonic Trackers

Use low-frequency ultrasound to measure position; Sound produced by a fixed triangular source (speakers); Each speaker is activated in cycle. The receiver is triangular and attached to the tracked

• bject and has three microphones;

Input Devices

Ultrasonic Trackers Ultrasonic Trackers

Distance is inferred from the sound time of flight; 9 distances are measured Sensitive to air temperature and other noise sources; Requires “direct line of sight”; Up to four receivers can be tracked using time multiplexing at the cost of reduced sampling rate. Slower than magnetic trackers (max 50 updates/sec). Should wait for echoes to die out Cheaper than magnetic trackers Input Devices

Ultrasonic tracker (Logitech) Input Devices

Typical operation range: 1.5m For larger work envelopes multiple

transmitters with overlapping tracking volumes can be used. – One transmitter is operational at each time instance

Large-volume ultrasonic tracker (Logitech) Input Devices 3D mouse

Optical Trackers Optical Trackers

Definition: A non-contact position measurement device that uses optical sensing to determine the real-time position/orientation of an object

Input Devices

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

Inside Inside-

• out optical tracker advantages
• ut optical tracker advantages

Input Devices Very large tracking surface and resistance to visual occlusions (line of sight).

Inside-looking-out LaserBIRD optical tracker Input Devices

Inside-looking-out LaserBIRD optical tracker Input Devices

HiBall HiBall 3000 wide area tracker 3000 wide area tracker

(courtesy of 3rdTech Inc.)

6 optical lenses 6 optical lenses HiBall HiBall Optical Sensor Optical Sensor HiBall HiBall Optical Sensor interior Optical Sensor interior Signal conditioning Signal conditioning electronics electronics 6 lateral 6 lateral-

• effect photodiodes

effect 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 HiBall 3000 tracker 3000 tracker

• n an HMD
• n an HMD

Lateral effect photo diodes

One LED is on at a time. A LED imaged by multiple sensors allows for position calculation

Types of VR Applications Types of VR Applications

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

Inertial Trackers Inertial Trackers

• Rate of change in orientation (angular velocity) is

measured by 3 gyroscopes.

• Rate of change in translation velocity (acceleration) is

measured by three accelerometers.

• Orientation/ position obtained by integration/double

integration of these quantities. Input Devices

Hybrid Ultrasonic/Inertial Trackers Hybrid Ultrasonic/Inertial Trackers

No interference from metallic objects; No interference from magnetic fields; No line of sight required; Large-volume tracking; “Source-less” orientation tracking; Full-room tracking; A newer technology. Input Devices

But But… …

Accelerometer errors Δa lead to decreased

accuracy since Δx= Δa t2 2

Errors in position grow geometrically in time! Gyroscope errors compound position errors; Needs independent position estimation to reduce

“drift” by resetting the data from inertial sensors.

• ---Hybrid Ultrasonic/Inertial Trackers

Hybrid Ultrasonic/Inertial Trackers Input Devices

Tracker components (InterSense Co.)

Base unit Sonic Strips

I-cube

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)

InterSense Stereo Glasses tracker (courtesy of Intersense Co.)

I-Cube Accel./gyro Ultrasonic emitter

InterSense Stereo stylus tracker (courtesy of Intersense Co.)

Accelerometer Ultrasonic emitter

IS 900 software block diagram IS 900 software block diagram

Link to VC 2.1 on book CD

Input Devices

Navigation and Gesture Input Devices Navigation and Gesture Input Devices

Navigation/manipulation interfaces allow

relative position control of virtual objects;

Usually incorporate some kind of tracking

device

Gesture interfaces allow dextrous

control of virtual objects and interaction through gesture recognition.

Input Devices

Absolute / relative measurements

Absolute measurements: actual position in a

fixed coordinate system – Never zero – Trackers provide absolute measurements

Relative measurements: changes from

previous position

Changes might not correspond to physical

quantities.

Absolute / relative measurements

Drawback of absolute measurement systems

(e.g. hand position trackers) for object manipulation in large VR scenes: limited arm reach.

Possible solution: multiply position with a

gain.

Navigation 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.

Input Devices

The Cubic Mouse Input Devices

Link to VC 2.2 on book CD

Trackballs Input Devices

Trackball

Measures three forces and three torques Can be used to incrementally change object

position and orientation.

Can be used as forces / torques applied on the

• bject and cause motion

Disadvantage: sensor coupling

– Nonzero sensed torques even if user applies pure forces – Object might rotate even when only translation is desired. – Can be programmed to read no torques.

The Microscribe (Immersion Co.) Input Devices

Gesture interfaces

Measure finger/wrist position and allow

interaction through gestures

More natural interaction than trackballs

cubic mouse, etc

No need for the user to hold some device

Gesture 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.

Input Devices

Hand / Finger Gestures

Pointing Release Grasp Translation Rotation Ring Okay Resize Viewpoint Transformation

Finger Degrees of Freedom Input Devices

Hand work envelope vs. interface type Input Devices

The Pinch Glove (Fakespace Co.)

• no joint measures, but contact detection

The Pinch Glove (Fakespace Co.)

Data Glove : Fiber Optic

How

– Attenuation of light transmitted from LEDs and carried through the optical fibers to phototransistors

Properties

– Fairly comfortable – Light – Optical fibers damage easily – Non-linear change between joint movement and sensed light

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 Glove

Glove has less sensors than hand joints … Needs to infer distal joint flexion angle

More sensors per finger can be used

5DT Data Glove Gesture library uses binary open/close configuration for 4 fingers by thresholding Input Devices

The CyberGlove (Immersion)

Uses 18-22 linear sensors – electrical strain gauges (resistance

changes with strain); Angles are obtained by measuring voltages on a Wheastone bridge; 112 gestures/sec. Sensor resolution 0.5 degrees, but errors accumulate to the fingertip (open kinematic chain); Defacto standard in high performance applications Needs calibration when put on the hand; Is expensive (about $10,000)

The CyberGlove (Vertex Co.)

Link to VC 2.3 on book CD

Special physical devices e.g a wand Special platforms e.g a cockpit

– Depending on the application