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CY3F8 Virtual Reality

7: In ut Devices andTracking Technologies

AB & FH Autumn 2010-11

InteractionandVR

Interactionwithavirtualworldisakey

ingredientofaVRexperience.

n e e , t e sp ayo av rtua wor

doesnotrespondatleasttoausers

physicalmovement,thenitisnot

consideredvirtualreality.

ShermanandCraig,2003

InteractionMethods Shouldbeeasyandintuitive

Areoftenunnatural(buthumansadapt)

Mayormaynotmimicreallife

familiaritywiththem

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InteractionTasks

1. Manipulation

Comprisingselectionandaction(sometimesperformedsimultaneously)

2. Navigation

Travel

Howtheusermovesthroughspace

Wayfinding

Howtheuserknowswheretheyareandwheretheyaregoing

InteractionTasks

3. Interactingwithothers

Sharedenvironments

Collaborativeenvironments

4. InteractingwiththeVR

system

e.g. Changingworld

parameters

TrackingTechnology Performance

CriteriaThefollowingcomefromS.Kalawsky TheScienceofVirtualReality:

Staticaccuracy: Theabilityofthetrackertodeterminethecoordinatesofapositioninspace.Thisisthevaluewithoutaveragingorsimilarfiltersapplied

DynamicAccuracy: Theaccuracyofthesystemasthesensorismoved.Highlydependantontheintegrationperiodofsamples,ifalonginte ration eriod is used then the d namic accurac ma be ver hi h

Latency: Thelatencyisthetimetakentogetnewdatafromthesensorsincludinghowquicklythesensorsrespondtochangesinposition.

Updaterate:Thetimetakentoprocessthedatafromthesensorsandcalculateaposition.Ifrunningfasterthanthecapture(latencypart)itmayreuseolddata(staticaccuracymaybehigh).Ahighupdateratealoneisntnecessarilyanadvantage.

PhaseLag:Thetotaltimedelayofthetrackersystem,i.e.latency+updaterateorthetrueageofanatomofdataasitleavesthetrackersystem.

Registration:Thecorrespondencebetweenactualpositionandreportedposition.Basicallycalibrationbothinitialandovertime,drift.

Signaltonoiseratio:Whatitsays,signalrelativetothebackgroundnoise.

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TrackingTechnology Performance

CriteriaButconsideralso:

Degreesoffreedompertarget Normallya3DoF trackerwillmeasureEITHERposition

x,y,z ORorientationroll,pitch,yaw

A6DoF trackerwillmeasurebothpositionand

Numberofsimultaneoustargets Sometrackingsystemcanttrackmanytargetsatonce

Othersmustreduceperformanceforeveryadditionaltargetduetolimitedbandwidthorsimilar

Workspace Sometrackershaveafixedmaximumworkspace,

othersmayloseperformanceasworkspaceincreases

MechanicalTrackers

Includesjoystickandmouse(older),

Moreusuallycablesandkinematiclinkswithsensorised joints

Pros:

oo accuracy,respons veness,registrationandrobustness.

Verylowlatency

Cons:

Tendtohavealimitedrangeofoperation.Physicallinkshaveafixedlength,cablesgettangledifrotated

Lowtransparency.

OpticalTrackers Active:LEDs

Passive:fiducials,retroreflective markers,naturalmarkersintheenvironment

Inherenttradeofbetweenaccuracyandrangeofoperation

Cangeteitherimageprocessingorfixedtransducertypes

Can be insideout or outsidein i.e. receivers are fixed ormobile Outsideinhastheadvantagethata

numberofcamerascanbeusedtotrackasingletargetwhichincreasesaccuracyandimproveslineofsight

Insideouthastheadvantageofbeingmaximallysensitivetoorientation

Imageprocessingsystemsrequirecontrolledlightconditions

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OpticalTrackers

Patternrecognitionsystemsusedtobeless

attractivebecausethecomputationwastoohighbutprocessingtimeisminimalnow

Pros: Highdatarates(muchfasterthansound),greatfor

rea me

Canbemadesimply,easyaccesstotechnology

Passivesystemsveryscalable(manytargets)

Cons: Lineofsight

Ambientnoise(evenforIR)

Nonuniformperformanceacrossaxes,oftendepthlessaccurate(samereasonashumans)

MagneticTrackers Forawhilemagnetictrackerswerethemostwidelyusedsolutionthough

notanylonger

ACtype(714Khzusually) Usesthreeaxismagneticdipolesourceandthreeaxismagneticsensors

Metallicorotherferrousmaterialsintheenvironment caninducedistortionsasACcauseseddycurrents(innewertechnologythiseffectisgreatlyreduced)

DCtype(pulsed) x

Leaveashorttimedelayforeddycurrentstodieout

Affectedbyanypermanentmagneticfield(earth,poweroutlets,motorsetc)

CanalsouseEarthmagneticfieldintentionallyforyawmeasurement

Pros: Veryresponsive,lowlatency

Cantrackmultipletargetsthoughupdateratedrops(probablynotmuchmorethan10atonceforrealtime)

Cons: Loseaccuracyandregistrationrapidlyasworkingvolumeincreases(S/Nratio

drops)

AcousticTrackers Useultrasoundeithertimeofflightorphasecoherentmeasurement

techniques.

Usuallytargethasemittersandreceiversareinfixedlocations.Canhavelotsofreceiverstomaximiselineofsight

Phasesystems: Betterperformancebecauseofhigherdatarates

Canoperatecontinuouslyratherthanhavingtowaitforanechotoreturn

,

Timeofflight: Morevulnerabletoacousticnoise.

Pros: Goodaccuracy,responsiveness,robustnessandregistration(ifworkspacekept

small)

Canhavemultipletargets(butatareductioninupdaterate)

Cons: Occludedsensorshaveabigimpactonperformance

Acousticpropertiesaffectedbyenvironment(humidity, temperature, pressure)butcanbecompensatedfor

Positionaccuracybetterthanorientation(unlesstargethasbiggapbetweenemitters)

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InertialTrackers Combinemultiaxisgyroscopes(angularvelocity)andaccelerometers

(MEMS)

Measurerollandpitchaccurately usingaccelerometers(earthgravityfield)

Yawmustbeintegratedfromgyromeasurement

Positionx,y,z muchlessaccurate.Accelerometersaredoubleintegratedtogetposition

rrorsaccumu a ew me:e.g.erroro . m s m g . error sdoubleintegrated: 0.0098t2/2=4.5metersafter30seconds

Filteringtechniquescanaccountforlargepartofwhitenoise(evenlydistributednoise)

CantaccountofGyroBiasDrift fundamentallimitationofgyros

Pros: Unlimitedworkingvolume

Nolineofsightissues

Tiltsensingveryaccurate

Highlyresponsive

Cons: Yawandpositionhasmeasurementdrift.Errorsaccumulatequicklyovertime.

SensorFusioninTrackers

Rarelyactuallyuseonetechnologyinisolation

Morecommontogetinformationfrommultiplesourcesandfusethedatatogetabetterestimate

CommonsensorfusiontechniquesincludeKalmanfilteringandBayesiannetworks

Inertialsensorsfororientationareusuallycombinedwitha3axismagnetometertoadjustforyawdrift

Inertialsensorsforpositionareveryoftencombinedwithopticaloracousticsensorstoaccountfordrift

Othersensingtechnologiesareusedsuchasforcesensors,bendsensors,capacitanceandGPSbutnormallyincombinationwiththemainonesthosealreadydiscussed

InputDevices Examples Standard keyboard and mouse

Joysticks

Wired gloves

Force balls

3D/6 DOF wands and mice

Speech recognition

Biosensors

Eye/gaze tracking

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MostrealtrackersliketheWii Remote

combinemultiplesensingtechnologies

Hasinertialcomponents(3axisaccelerometerand3axisgyro)

InputDevices Wii Remote

Opt ca components.H g spee cmos cameraontheremote(insidelookingout)withanIRpassfilterdetects4IRLEDsonthesensorbar

http://www.youtube.com/watch?v=Jd3 eiidUw

InputDevices MSKinect Widevarietyofinputtypes:

capableofgesture,faceandspeechrecognition

Normalcameraplus2camerasfordepthsensingand4microphones

De th sensin works b ro ectin a attern on thescene(presumablyinIR).Twocamerasfordeptharesensitivetopattern.Patternisdenserthefurtheraway

itis Normalcamera+depthsensingusedtogetherto

isolateindividualusersandfindfacialcharacteristicsandgestures

Speechrecognitioncanisolateseparatevoicecommands(probablyusingsomethinglikeICA)andselectwhichpersonistalkingfromcamerafeed