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Input devices and interaction
Ruth Aylett
Contents
Tracking– What is available
Devices– Gloves, 6 DOF mouse,
WiiMote
Why is it important?
Interaction is basic to VEs– We defined them as ‘interactive in real-time’
No interaction => NOT a VE Ideal interaction:
– Very low latency - i.e fast– Multi-modal– Unencumbered– Intuitive
Technology falls well short of this of course
Tracking the human body
Large displays require position and orientation of viewer’sbody to be tracked– tracking information fed to runtime system as input signal.
Most commonly tracked is head butsometimes also hands, arms,legs, eyes etc.– Head tracking used to update virtual
viewpoint orientations.
Body tracking needed for lifelikeinteraction with objects and creatures.– say user wishes to wave at another person
in the VE: their real-world motions can betracked and replicated in the VE.
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Interaction types
Navigation– Staying on the ground?– Walking v flying
• Depends on size of model wrt display system• Degree of immersion
Interaction with other users– Gesture
Interaction with objects– Depends on the object and interaction– Select, lift, rotate, throw, steer, hit
Virtual Tennis
MovieVirtual Tennis
Tracking the human head
An essential basic requirement in immersive VRsystems.
Imagine axes mounted on top of your head– pans, tilts and yaws of head
measured around those axes.
HMDs often have rotation sensorsto measure these three angles.
Angles passed to run-time VRsoftware which updates viewingangles.
HMD
Tracking devices
Many tracking devices and systems developed over theyears– some aimed specifically at VR systems– others borrowed from other areas.
Some systems are portable and cheap - some requirepermanent installations in large rooms and are veryexpensive indeed.– Trackers can be magnetic, electro-magnetic, acoustic, inertial,
optical, or mechanical. Electro-magnetic trackers
– transmitter generates electromagnetic signals– received by a receiver (or sensor).– Signal strength used to determine absolute position and
orientation of receiver relative to transmitter.
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Example: Polhemus FASTRAK
FASTRAK electro-magnetic sensor from Polhemus– accurately computes the position and orientation of tiny receiver
as it moves through space. Dynamic, real time six degree-of-freedom measurement
of position (X, Y, and Z) and orientation (yaw, pitch, androll)– RS-232 signal updated at 120 records/sec.
Transmitter constantly puts out a weak magnetic field.– passive receiver generates an electric signal as it is moved
through the field.
– Polhemus' processing electronics then amplify and analyse thissignal to determine the real-world position and orientation of thereceiver relative to the transmitter.
Polhemus FASTRAK system
Polhemous trackers well proven and widely used since thevery early 1990’s.
The FASTRAK system shownhere has one receiverand one transmitter.
System expandedby adding up to three morereceivers– can attach receivers to
different parts of body– log data for gait and limb
analysis or computeranimation.
Electromagnetic TrackingPolhemus
Electromagnetic TrackingAscension
Ascension market a number of systems based on DCrather than AC fields including Flock of Birds and a full
gait analysis system called MotionStar.
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Electromagnetic TrackingAdvantages Small receivers Reasonably cheap Line-of-sight (LOS) not requiredDisadvantages Accuracy diminishes with distance Not very large working volume High latency due to filtering Transmitter/receiver required
Electro-magnetic interference
Major problem of electro-magnetic trackers– magnetic fields easily affected by the surrounding environment.
Large metal objects produce eddy currents in thepresence of the magnetic fields– These can interfere and distort the original signal causing
inaccurate measurements.– same effect appears near electric currents, such as in cabling– also ferromagnetic materials– Also electromagnetic sources such as computer monitors.
Ferromagnetic and/or metal surfaces cause fielddistortion
Ultrasonic trackers
Two main components– transmitter generating an ultrasound signal– receiver detecting the signal.
Distance is calculated bymeasuring time-of-flightof ultrasonic pulse.– Three transmitters and receivers
needed to calculate full 3Dposition and orientation.
Ultrasonic tracking used by Logitech Head Tracker(shown) and 3D mouse.
Ultrasonic trackers
The Power Glove made by toycompany Mattel (who make Barbie)– introduced in 1989 for use with
the Nintendo EntertainmentSystem (NES).
Ultrasonic device for use in place ofstandard Nintendo controllers
Detected finger motion– Plus full set of buttons on the wrist.
In fact not much use for Nintendogamers– But amazingly advanced piece of VR
kit for its time.
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Acoustic Tracking
Advantages Well known transducers (mics), lightweight Low cost deviceDisadvantages Line-of-sigh (LOS) required Echoes Low accuracy (speed of sound in air varies) Transmitter/receiver required
Inertial tracking systems
Very popular (because cheap)– based on inertial gyro technology– Detects acceleration and thus can calculate velocity (since mass
in known) giving 3DoF– Newish example is the Intersense IS-300.
Can be coupled with ‘add-on’ ultrasonic system to give 6DoF sensing– example of a hybrid technology tracker.
IS-300 can operate in metallicenvironments,– 6 DoF tracker operates only
in LoS of transmitter.
Other examples:Intersense Intertrax2 and the Ascension 3D-Bird.
Inertial TrackingAdvantages Cheap Small size No transmitter/receiver required LOS not requiredDisadvantages Only 3 DOF on their own Drift Not accurate for slow movements
Optical tracking methods
Many different forms– Often use image processing and pattern recognition and matching– Much work outside of VR: numerous ideas suitable for tracking
object position and pose
For example fiducial mark detection– light sources or reflective
colour markers attached toobject at important locations suchas joints or extremities.
Easier for image processingalgorithm to track in clutteredconditions.
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How it is doneOptical tracking methods
Outside-in tracker– tracking apparatus is fixed– object to be tracked (e.g. the user) is viewed from the "outside".
Inside-out systems– take tracking measurements from the object to be tracked– for instance a camera can be mounted on the HMD– images analysed to produce pose and distance estimations based on
the position of fixed patterns within the environment.
Visible images or infra-red used. Many optical systems (but not all!) are one-offs, expensive
and require careful calibration procedures.
Infra-red cameras Optical Tracking
Advantages Can work over a large area. Inherently wirelessDisadvantages LOS needed Transmitter/receiver required Expensive Requires computer vision technology
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Eye trackers
Eye tracking systems are examples of optical trackingdevices.– viewpoint in the virtual world follows
the gaze of user’s eye.
Originally developed as a mousereplacement– simply look at object– interact through eye movement
(such as a slow blink).
Support physically impaired users. Combined eye and head tracking systems
• also exist - use in practice is complicated.
Mechanical trackers
Mechanical linkage system– arm-like structure of several joint, one end fixed, the
other free to move with the user.
Measure position and angular orientation of freeend– by measuring angles at each joint and
factoring in length of each segment.
Fake Space BOOM (right)
Mechanical TrackingAdvantages Simple sensors, no need for transmitter/receiver low-cost device very low latency High positional accuracyDisadvantages The user is tethered Lots of inertia Typically small working volume Mechanical parts wear out
Unencumbered tracking
Depends on identifying hand/hand onvideo– One approach is using blobs
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Cybergloves and similar
Inherent in the folklore and hype of VR is the cyberglove- a wearable device that monitors the the position andorientation of hand and fingers.
The name CYBERGLOVE® isregistered by Virtual Technologies Inc(VTi).– uses 18 or 22 patented
angular sensors for tracking theposition of fingers and hand.
Gloves
Virtual TechnologiesCyberGlove
- 18-sensor model - 22-sensor modelVariants are: - CyberTouch - CyberGrasp
GlovesFifth Dimensions Technologies - Data Glove
Data Glove finger flexure hand orientation -roll & pitch
Gloves
Fakespace - Pinch GlovePinch Glove gesture recognition reliable low cost electrical sensors in
each fingertip contact among any 2 or more
digits
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Mouse as input device in VR
Normal 2D mouse can be used (as in Cortonafor example).– Need user selectable modes to switch between
DoF’s.
More sophisticated mice provide 3 or moreDoF: these include the Spaceball (shownhere) and Spacemouse.
Standard games joysticks orgamepads also usedto give 2 or more DoF’s.
6 DOF “Mice”
3 translation DOF 3 rotation DOF
6 DOF “Mice”Spaceball
byLabtec
Spacemouse by DLR (Logitech - USA)
6 DOF “Mice”
CyberpuckSpaceOrb
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The WiiMote
3 accelerometers– Enough for 6 DOF– But will drift– Bluetooth connection to
10m
Optical (IR) sensor– To 5m from sensor bar– Triangulation from ends of
bar– Allows accurate pointing
Speaker
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