Jan 9Jan 9 11

TrackingTrackingSherman & Craig, pp. 75-94.Sherman & Craig, pp. 75-94.

Welch, Greg and Eric Foxlin (2002). “Welch, Greg and Eric Foxlin (2002). “Motion Tracking: No Silver Bullet, but a Motion Tracking: No Silver Bullet, but a Respectable ArsenalRespectable Arsenal,” IEEE Computer Graphics and Applications, special issue ,” IEEE Computer Graphics and Applications, special issue

on “Tracking,” November/December 2002, 22(6): 24–38.. on “Tracking,” November/December 2002, 22(6): 24–38.. (http://www.cs.unc.edu/~tracker/media/pdf/cga02_welch_tracking.pdf)(http://www.cs.unc.edu/~tracker/media/pdf/cga02_welch_tracking.pdf)

Jan 9Jan 9 22

MotivationMotivation Methods to interact with the Methods to interact with the

virtual worldvirtual world– More naturalMore natural– Higher level of immersionHigher level of immersion– Task performanceTask performance– Control navigationControl navigation– Control interactionControl interaction– Ex. Training soldiers w/ a Ex. Training soldiers w/ a

gungun How do we track the gun?How do we track the gun? How do we determine what How do we determine what

the user sees?the user sees?

This requires:This requires:– Signaling (button presses, Signaling (button presses,

etc.)etc.)– Location. <- this is tracking!Location. <- this is tracking!

Jan 9Jan 9 33

TrackingTracking http://www.sv.vt.edu/future/vt-c

ave/apps/#detour PosePose

– PositionPosition– OrientationOrientation

What do we want to What do we want to track?track?– Head poseHead pose– Hand poseHand pose– Other body partOther body part– Other objects (e.g. Other objects (e.g. spider))

So what does it mean if So what does it mean if a tracking system a tracking system reports your head at reports your head at 2.5,3.3, 1.9?2.5,3.3, 1.9?

Common Tracking MethodsCommon Tracking Methods

GPSGPS WiiWii

Jan 9Jan 9 44

http://www.directionsmag.com/images/articles/GPS_articles/realtime_diff_GPS.jpg

Jan 9Jan 9 55

Basic IdeaBasic Idea

X

Y

Z

Trackers provide location and/or position information relative to some coordinate system.

(x,y,z) (rx,ry,rz)

(0,0,0) Origin for tracker coordinate system

(0,0,0) Receiver coordinate

system

Jan 9Jan 9 66

Degrees of freedomDegrees of freedomThe amount of pose information returned by the tracker

Position (3 degrees)Orientation (3 degrees)

There are trackers that can do:•only position•only orientation•both position and orientation

Jan 9Jan 9 77

QuestionQuestion

Given that I want to track your head, I attach a Given that I want to track your head, I attach a new tracker from NewTracker Corp. it returns 6 new tracker from NewTracker Corp. it returns 6 degrees of freedom (6 floats). What questions degrees of freedom (6 floats). What questions should you have?should you have?

What are some evaluation points for a tracking What are some evaluation points for a tracking system?system?

Jan 9Jan 9 88

Evaluation CriteriaEvaluation Criteria Data returned Data returned Spatial distortion Spatial distortion

(accuracy) (accuracy) ResolutionResolution Jitter (precision) Jitter (precision) DriftDrift LagLag Update RateUpdate Rate RangeRange

Interference and noiseInterference and noise Mass, Inertia and Mass, Inertia and

EncumbranceEncumbrance Number of Tracked Number of Tracked

Points DurabilityPoints Durability WirelessWireless Price Price

Which of these are most important?

Jan 9Jan 9 99

Performance MeasuresPerformance Measures Registration (Accuracy)Registration (Accuracy) – –

– Difference between an object’s Difference between an object’s pose and the reported posepose and the reported pose

– LocationLocation– OrientationOrientation– What are determining factors?What are determining factors?

ResolutionResolution – Granularity that the tracking Granularity that the tracking

system can distinguish system can distinguish individual points or orientationsindividual points or orientations

– What are determining factors?What are determining factors? Jitter Jitter

– Change in reported position of Change in reported position of a stationary objecta stationary object

– What are determining factors?What are determining factors? Drift Drift

– Steady increase in error with Steady increase in error with timetime

– What are determining factors?What are determining factors?

Jan 9Jan 9 1010

Performance MeasuresPerformance Measures

tt00 – – time when sensor time when sensor is at point is at point pp

tt11 – – time when sensor time when sensor reports reports pp

Lag Lag or or Latency Latency – – tt1 1 --

tt00 What makes up What makes up

latency?latency?– AcquisitionAcquisition– TransmissionTransmission– FilteringFiltering

Jan 9Jan 9 1111

Performance MeasuresPerformance Measures

tt00 – – time when time when sensor sensor

is at point is at point pp tt11 – – time when sensor time when sensor

reports reports pp Lag Lag or or Latency Latency – – tt1 1 -- tt00 What makes up What makes up

latency?latency?– AcquisitionAcquisition– TransmissionTransmission– FilteringFiltering

What is a minimum?What is a minimum?

Jan 9Jan 9 1212

Update RateUpdate Rate

Number of tracker Number of tracker position/orientation position/orientation samples per secondsamples per second– High update rate != High update rate !=

accuracyaccuracy– Poor use of update Poor use of update

information may result in information may result in more inaccuracy more inaccuracy

– Communication pathways Communication pathways and data packet size are and data packet size are importantimportant

Jan 9Jan 9 1313

RangeRange Working volumeWorking volume

– What is the shape?What is the shape?– Accuracy decreases with Accuracy decreases with

distancedistance– Range is inversely Range is inversely

related to accuracyrelated to accuracy Position and Position and

orientation range could orientation range could be differentbe different

Sensitivity not uniform Sensitivity not uniform across all axisacross all axis

Jan 9Jan 9 1414

Interference and NoiseInterference and Noise Interference - Interference -

external external phenomenon that phenomenon that degrades system’s degrades system’s performanceperformance

Each type of tracker Each type of tracker has different causes has different causes of of interference/noiseinterference/noise

OcclusionOcclusion MetalMetal NoiseNoise Environmental (e.g. Environmental (e.g.

door slamming, air door slamming, air conditioner)conditioner)

Jan 9Jan 9 1515

Mass, Inertia and Mass, Inertia and EncumbranceEncumbrance

Do you really want Do you really want to wear this?to wear this?

InertiaInertia TetheredTethered

Jan 9Jan 9 1616

Multiple Tracked PointsMultiple Tracked Points Number of potentially Number of potentially

tracked pointstracked points– UniqueUnique– SimultaneousSimultaneous

DifficultiesDifficulties– Interference between the Interference between the

sensorssensors– MultiplexingMultiplexing

Time Multiplexing Time Multiplexing – Update rate – Update rate of S samples per second and N of S samples per second and N sensors results in S/N samples sensors results in S/N samples per sensor per secondper sensor per second

Frequency Multiplexing Frequency Multiplexing – Each – Each sensor broadcasts on a sensor broadcasts on a different frequency. More $$different frequency. More $$

Jan 9Jan 9 1717

PricePrice

You get what you You get what you pay for. ($30-pay for. ($30-$100k+)$100k+)

Rich people are a Rich people are a small market.small market.

Jan 9Jan 9 1818

Tracking TechnologiesTracking Technologies

Different Tracking TechnologiesDifferent Tracking Technologies Goals:Goals:

– Understand how they workUnderstand how they work– Understand tradeoffsUnderstand tradeoffs– Know when to use whichKnow when to use which– Future directionsFuture directions

Jan 9Jan 9 1919

Mechanical LinkageMechanical Linkage

Rigid jointed structureRigid jointed structure One end (base) is fixedOne end (base) is fixed The other (distal) is freeThe other (distal) is free Distal is user controlled to an Distal is user controlled to an

arbitrary position and orientation.arbitrary position and orientation. Sensors at the joints detect the Sensors at the joints detect the

angleangle Concatenate translates and rotates Concatenate translates and rotates Determine the position and Determine the position and

orientation of the distal relative to orientation of the distal relative to the base.the base.

Jan 9Jan 9 2020

Mechanical Mechanical TrackingTracking

Pros:Pros:– AccurateAccurate– FastFast– Low lagLow lag– Minimal environmental Minimal environmental

interferenceinterference– No calibrationNo calibration– Can incorporate force Can incorporate force

feedbackfeedback Cons:Cons:

– Low range (effectively 5’ – Low range (effectively 5’ – does not scale well)does not scale well)

– CostCost– 1 tracked point 1 tracked point

(body/others are hard to (body/others are hard to track)track)

Data returned: 6 DOFData returned: 6 DOF Spatial distortion – 0.3381 mmSpatial distortion – 0.3381 mm Resolution – very highResolution – very high Jitter (precision) – very lowJitter (precision) – very low Drift - noneDrift - none Lag – >5msLag – >5ms Update Rate - 300 HzUpdate Rate - 300 Hz Range - 8 ftRange - 8 ft Number of Tracked Points – 1Number of Tracked Points – 1 Wireless - noWireless - no Interference and noise – metal, Interference and noise – metal,

earthearth Mass, Inertia and Encumbrance – Mass, Inertia and Encumbrance –

substantial substantial Durability – lowDurability – low Price – highPrice – high

Jan 9Jan 9 2121

Mechanical Mechanical Tracking ProductsTracking Products

Fake Space Labs Fake Space Labs BOOM Display BOOM Display (discontinued)(discontinued)

Sensible PhantomSensible Phantom

Jan 9Jan 9 2222

ElectromagnetiElectromagnetic Trackersc Trackers

EmitterEmitter– Apply current through coilApply current through coil– Magnetic field formedMagnetic field formed– 3 orthonormal coils to 3 orthonormal coils to

generate fieldsgenerate fields SensorSensor

– Strength attenuated by Strength attenuated by distancedistance

– 3 orthonormal magnetic-3 orthonormal magnetic-field-strength sensorsfield-strength sensors

– Determine the absolute Determine the absolute position and orientation of position and orientation of a tracker relative to a a tracker relative to a source.source.

Polhemus (a.c.)Polhemus (a.c.) Ascension (d.c.)Ascension (d.c.)

Jan 9Jan 9 2323

Basic Basic Principles of Principles of EM TrackersEM Trackers

Pulse the emitter coils in Pulse the emitter coils in successionsuccession

Sensor contains 3 Sensor contains 3 orthogonal coilsorthogonal coils

For each pulse, sensor For each pulse, sensor measures the strength of measures the strength of the signal its 3 coils (9 total the signal its 3 coils (9 total measurements)measurements)

Known:Known:– Pulse strength at the Pulse strength at the

sourcesource– Attenuation rate of field Attenuation rate of field

strength with distancestrength with distance Calculate position and Calculate position and

orientation of the sensor orientation of the sensor coilscoils

Jan 9Jan 9 2424

EM TrackersEM Trackers Data returned: 6 DOFData returned: 6 DOF Spatial distortion – 0.6 mm, Spatial distortion – 0.6 mm,

0.0250.025°° Resolution – 0.00508 mm, Resolution – 0.00508 mm,

0.0250.025° / inch from receiver° / inch from receiver Jitter (precision) – mm to cmJitter (precision) – mm to cm Drift - noneDrift - none Lag – reported 4 msLag – reported 4 ms Update Rate - 120 HzUpdate Rate - 120 Hz Range - 5 ftRange - 5 ft Number of Tracked Points – 16 Number of Tracked Points – 16

(divides update rate)(divides update rate) Wireless - yesWireless - yes Interference and noise – metal, Interference and noise – metal,

earthearth Mass, Inertia and Encumbrance - Mass, Inertia and Encumbrance -

minimalminimal Durability - highDurability - high Price - $4000+Price - $4000+

Jan 9Jan 9 2525

EM TrackersEM Trackers

Pros:Pros:– Measure position and orientation in Measure position and orientation in

3D space3D space– Does not require direct line of sightDoes not require direct line of sight– Low encumbranceLow encumbrance– CostCost– Good performance close to emitterGood performance close to emitter– LagLag– Can be built ‘into’ devicesCan be built ‘into’ devices– Earth magnetic field good for 3DOFEarth magnetic field good for 3DOF

Cons:Cons:– Accuracy affected by Accuracy affected by

DC: DC: FerrousFerrous metal and metal and electromagnetic fields. electromagnetic fields.

AC: Metal and electromagnetic fieldsAC: Metal and electromagnetic fields– Operate on only one side of the Operate on only one side of the

source (the working hemisphere)source (the working hemisphere)– Low range (effectively 5’ – does not Low range (effectively 5’ – does not

scale well)scale well)– CalibrationCalibration

Data returned: 6 DOFData returned: 6 DOF Spatial distortion – 0.6 mm, Spatial distortion – 0.6 mm,

0.0250.025°° Resolution – 0.00508 mm, Resolution – 0.00508 mm,

0.0250.025° / inch from receiver° / inch from receiver Jitter (precision) – mm to cmJitter (precision) – mm to cm Drift - noneDrift - none Lag – reported 4 msLag – reported 4 ms Update Rate - 120 HzUpdate Rate - 120 Hz Range - 5 ftRange - 5 ft Number of Tracked Points – 16 Number of Tracked Points – 16

(divides update rate)(divides update rate) Wireless - yesWireless - yes Interference and noise – metal, Interference and noise – metal,

earthearth Mass, Inertia and Encumbrance - Mass, Inertia and Encumbrance -

minimalminimal Durability - highDurability - high Price - $4000+Price - $4000+

Jan 9Jan 9 2626

EM TrackingEM Tracking

Ascension Flock of Ascension Flock of BirdsBirds

Polhemus FastrakPolhemus Fastrak Extremely popularExtremely popular Good for many Good for many

applicationsapplications– CAVEs (remove CAVEs (remove

metal)metal)– HMDsHMDs– Projection displaysProjection displays– FishtankFishtank

Jan 9Jan 9 2727

Acoustic/Ultrasonic TrackingAcoustic/Ultrasonic Tracking Time of Flight TrackingTime of Flight Tracking

– EmittersEmitters Multiple emittersMultiple emitters In succession, emit sound In succession, emit sound

(record time)(record time)– ReceiverReceiver

Report time of receiving Report time of receiving soundsound

Frequency tunedFrequency tuned– Calculate time-of-flight Calculate time-of-flight

(1000 feet/sec)(1000 feet/sec)– Use ultrasonic (high) Use ultrasonic (high)

frequenciesfrequencies– Similar:Similar:

EM trackingEM tracking Radar/sonarRadar/sonar

Phase Coherence trackingPhase Coherence tracking– Orientation onlyOrientation only– Check phase of received Check phase of received

signalsignal

Jan 9Jan 9 2828

Ultrasonic Tracking System Ultrasonic Tracking System SetupSetup

Stationary Origin(receivers)

Tracker(transmitters)distance1

distance2

distance3

How much data does 1 transmitter provide?How much data do 2 transmitters provide?How much data do 3 transmitters provide?

Jan 9Jan 9 2929

Acoustic/Ultrasonic Tracking Acoustic/Ultrasonic Tracking CharacteristicsCharacteristics

Pros:Pros:– Inexpensive Inexpensive – Wide areaWide area– EncumbranceEncumbrance

ConsCons– InaccurateInaccurate– InterferenceInterference– Requires line-Requires line-

of-sightof-sight

Data returned: 3 or 6 DOFData returned: 3 or 6 DOF Spatial distortion – low (good Spatial distortion – low (good

accuracy)accuracy) Resolution – goodResolution – good Jitter (precision) – mm to cmJitter (precision) – mm to cm Drift - noneDrift - none Lag – very slowLag – very slow Update Rate - 120 HzUpdate Rate - 120 Hz Range – 40’+ (scaling issues)Range – 40’+ (scaling issues) Number of Tracked Points – Number of Tracked Points –

numerous (spread-spectrum)numerous (spread-spectrum) Wireless - yesWireless - yes Interference and noise – medium, Interference and noise – medium,

noise, environmentnoise, environment Mass, Inertia and Encumbrance - Mass, Inertia and Encumbrance -

minimalminimal Durability - highDurability - high Price – cheap to $12000+Price – cheap to $12000+

Jan 9Jan 9 3030

Ultrasonic Tracking DevicesUltrasonic Tracking Devices– LogitechLogitech– Mattel Power GloveMattel Power Glove– Intersense Intersense – Used as part of Used as part of

hybrid systemshybrid systems

Jan 9Jan 9 3131

Inertial TrackingInertial Tracking Electromechanical Electromechanical

devices devices Detect the relative Detect the relative

motion of sensors motion of sensors Measuring change:Measuring change:

– Acceleration Acceleration (accelerometers)(accelerometers)

– Gyroscopic forces Gyroscopic forces (electronic gyroscopes (electronic gyroscopes piezo electric)piezo electric)

– Inclination (inclinometer)Inclination (inclinometer) Frameless trackingFrameless tracking

– Known startKnown start– Each reading updates Each reading updates

current positioncurrent position

Jan 9Jan 9 3232

AccelerometersAccelerometers Mounted on to body partsMounted on to body parts Detects accelerationDetects acceleration Acceleration is integrated Acceleration is integrated

to find the velocityto find the velocity Velocity is integrated to Velocity is integrated to

find positionfind position Unencumbered and large Unencumbered and large

area tracking possiblearea tracking possible Difficult to ‘factor’ out Difficult to ‘factor’ out

gravitygravity

Jan 9Jan 9 3333

Accelerometer Tracking Accelerometer Tracking ErrorsErrors

Suppose a constant error Suppose a constant error ii, so that , so that measured acceleration is ameasured acceleration is aii(t)+ (t)+ ii

vvii(t) = (t) = (a(aii(t)+ (t)+ ii)dt = )dt = a aii(t)dt + (t)dt + iitt

xxii(t) = (t) = v vii(t)dt = (t)dt = (( a aii(t)dt + (t)dt + t)dt t)dt

xxii(t) = (t) = a aii(t)dtdt + 1/2 (t)dtdt + 1/2 iitt22

Errors accumulate since each position is Errors accumulate since each position is measured relative to the last positionmeasured relative to the last position

Estimated 10 degrees per minute. How is Estimated 10 degrees per minute. How is this related to drift? this related to drift?

Jan 9Jan 9 3434

Inertial TrackingInertial Tracking

InclinometerInclinometer– Measures Measures

inclinationinclination– Relative to some Relative to some

“level” position“level” position

Gyroscopes Gyroscopes – Resist rotationResist rotation– Measure resistanceMeasure resistance

Jan 9Jan 9 3535

Inertial Tracking Systems Inertial Tracking Systems CharacteristicsCharacteristics

Pros:Pros:– Inexpensive Inexpensive – Wide areaWide area– Orientation very Orientation very

accurateaccurate– Minimal interferenceMinimal interference– EncumbranceEncumbrance

ConsCons– Position poorPosition poor– Need to recenterNeed to recenter– CalibrationCalibration– Inaccurate over timeInaccurate over time– DriftDrift

Data returned: 3 or 6 DOFData returned: 3 or 6 DOF Spatial distortion – low (good Spatial distortion – low (good

accuracy)accuracy) Resolution – goodResolution – good Jitter (precision) – lowJitter (precision) – low Drift - highDrift - high Lag – very lowLag – very low Update Rate - highUpdate Rate - high Range – very largeRange – very large Number of Tracked Points – 1Number of Tracked Points – 1 Wireless - yesWireless - yes Interference and noise – gravityInterference and noise – gravity Mass, Inertia and Encumbrance - Mass, Inertia and Encumbrance -

minimalminimal Durability - highDurability - high Price – cheapPrice – cheap

Jan 9Jan 9 3636

Optical TrackersOptical Trackers Use vision based systems Use vision based systems

to track sensorsto track sensors Outside-Looking In:Outside-Looking In:

– Cameras (typically fixed) in Cameras (typically fixed) in the environment the environment

– Track a marked pointTrack a marked point– PPT tracker from WorldViz (PPT tracker from WorldViz (

www.worldviz.com))– Older optical trackersOlder optical trackers

Inside-Looking Out:Inside-Looking Out:– Cameras carried by Cameras carried by

participantparticipant– Track makers (typically Track makers (typically

fixed) in the environmentfixed) in the environment– Intersense Optical TrackerIntersense Optical Tracker– 3rdTech HiBall Tracker3rdTech HiBall Tracker

Image from: High-Performance Wide-Area Optical Tracking The HiBallTracking System, Welch, et. al. 1999.

Jan 9Jan 9 3737

Outside Looking In Outside Looking In Optical TrackingOptical Tracking

Precision Point Tracking by Precision Point Tracking by WorldVizWorldViz

IR Filtered Cameras are IR Filtered Cameras are calibratedcalibrated– IntrinsicsIntrinsics

Focal length, Center of Focal length, Center of projection, aspect ratioprojection, aspect ratio

– ExtrinicisExtrinicis Position and orientation in Position and orientation in

world spaceworld space Each frame:Each frame:

– Get latest images of pointGet latest images of point– Generate a ray (in world Generate a ray (in world

coordinates) through the coordinates) through the point on the image planepoint on the image plane

– Triangulate to get positionTriangulate to get position

Jan 9Jan 9 3838

Outside Looking In Outside Looking In Optical TrackingOptical Tracking

What factors play a What factors play a role in O-L-I tracking?role in O-L-I tracking?– Camera resolutionCamera resolution– Frame rateFrame rate– Camera calibrationCamera calibration– OcclusionOcclusion– CCD QualityCCD Quality

How does it do for:How does it do for:– PositionPosition

stable, very goodstable, very good– OrientationOrientation

Unstable, poorUnstable, poor– LatencyLatency

Cameras are 60HzCameras are 60Hz

Jan 9Jan 9 3939

OrientationOrientation How to How to

compensate for compensate for poor orientation?poor orientation?– Combine with Combine with

orientation only orientation only sensor (ex. sensor (ex. Intersense’s Intersense’s InertiaCube)InertiaCube)

Also known as:Also known as:– ‘‘Hybrid tracker’Hybrid tracker’– ‘‘Multi-modal Multi-modal

tracker’tracker’ Position: visionPosition: vision Orientation: inertialOrientation: inertial

Jan 9Jan 9 4040

Inside-Looking-OutInside-Looking-OutOptical TrackingOptical Tracking

Tracking device Tracking device carries the cameracarries the camera

Tracks markers in Tracks markers in the environmentthe environment

Intersense TrackerIntersense Tracker 3rdTech HiBall 3rdTech HiBall

TrackerTracker

Images from: High-Performance Wide-Area Optical Tracking The HiBallTracking System, Welch, et. al. 1999.

Jan 9Jan 9 4141

HiBall TrackerHiBall Tracker

Six Lateral Effect PhotoDioides (LEPDs) inHiBall. Think 6 cameras.

–Position•Pretty good

–Orientation•Very good

–Latency•LEPDs can operate at 1500 Hz

Jan 9Jan 9 4242

LED Optical LED Optical TrackersTrackers

SensorsSensors– Webcameras Webcameras – Photodiodes Photodiodes

TrackTrack– LEDsLEDs– Reflected LED lightReflected LED light

Why LEDs?Why LEDs?– Easy to trackEasy to track– Grab your webcam and Grab your webcam and

point a remote at itpoint a remote at it Super cheapSuper cheap P5 GloveP5 Glove Nintendo WiiNintendo Wii WorldViz PPTWorldViz PPT Virtual PatientsVirtual Patients

Jan 9Jan 9 4343

Optical Tracking ReviewOptical Tracking Review

Pros:Pros:– Inexpensive Inexpensive – Wide areaWide area– Very accurateVery accurate

ConsCons– High quality is very High quality is very

expensiveexpensive– OcclusionOcclusion– CalibrationCalibration

Data returned: 6 DOFData returned: 6 DOF Spatial distortion – very low (very Spatial distortion – very low (very

good accuracy)good accuracy) Resolution – very goodResolution – very good Jitter (precision) – very goodJitter (precision) – very good Drift - noneDrift - none Lag – moderateLag – moderate Update Rate – low - highUpdate Rate – low - high Range – very large (40’ x 40’ +)Range – very large (40’ x 40’ +) Number of Tracked Points – 4Number of Tracked Points – 4 Wireless - yesWireless - yes Interference and noise – occlusionInterference and noise – occlusion Mass, Inertia and Encumbrance - Mass, Inertia and Encumbrance -

moderatemoderate Durability – low - highDurability – low - high Price – cheap to very expensivePrice – cheap to very expensive

Hybrid ApproachesHybrid Approaches

Nintendo WiiNintendo Wii

Jan 9Jan 9 4444

Jan 9Jan 9 4545

Angle MeasurementAngle Measurement

Measurement of the Measurement of the bend of various joints bend of various joints in the user’s bodyin the user’s body

Used for:Used for:– Reconstruction of the Reconstruction of the

position of various body position of various body parts (hand, torso).parts (hand, torso).

– Measurement of the Measurement of the motion of the human motion of the human body (medical)body (medical)

– Gestural InterfacesGestural Interfaces Sign languageSign language

Jan 9Jan 9 4646

Angle Measurement Angle Measurement TechnologyTechnology

Optical SensorsOptical Sensors– Emitter and receiver on Emitter and receiver on

ends of sensorends of sensor– As sensor is bent, the As sensor is bent, the

amount of light from amount of light from emitter to receiver is emitter to receiver is attenuatedattenuated

– Attenuation is Attenuation is determined by bend determined by bend angleangle

– Examples: Flexible hollow Examples: Flexible hollow tubes, optical fiberstubes, optical fibers

– VPL Data GloveVPL Data Glove

Jan 9Jan 9 4747

Angle Measurement Angle Measurement Technology Technology (cont.)(cont.)

Strain SensorsStrain Sensors– Measure the Measure the

mechanical strain mechanical strain as the sensor is as the sensor is bent. bent.

– May be mechanical May be mechanical or electrical in or electrical in nature.nature.

– P5 Glove $25 (!)P5 Glove $25 (!)– Cyberglove (Virtual Cyberglove (Virtual

Technologies)Technologies)

Jan 9Jan 9 4848

Joints and Cyberglove Joints and Cyberglove SensorsSensors

InterphalangealJoint (IP)

MetacarpophalangealJoint (MCP)

Thumb RotationSensor

Proximal Inter-phalangeal Joint (PIP)

MetacarpophalangealJoint (MCP)

Abduction Sensors

Jan 9Jan 9 4949

Angle Measurement Angle Measurement Technology Technology (cont.)(cont.)

Exoskeletal Exoskeletal StructuresStructures– Sensors mimic joint Sensors mimic joint

structurestructure– Potentiometers or Potentiometers or

optical encoders in optical encoders in joints report bendjoints report bend

– Exos Dexterous Exos Dexterous Hand MasterHand Master

Jan 9Jan 9 5050

Other TechniquesOther Techniques

Pinch GlovesPinch Gloves– Have sensor Have sensor

contacts on the contacts on the ends of each fingerends of each finger

Jan 9Jan 9 5151

TechnologyTechnology

DatagloveDataglove– Low accuracyLow accuracy– Focused resolutionFocused resolution

MonkeyMonkey– High accuracyHigh accuracy– High data rateHigh data rate– Not realistic Not realistic

motionmotion– No paid actorNo paid actor

Mechanical motion capture

Jan 9Jan 9 5252

TechnologyTechnology

Exoskeleton + angle sensorsExoskeleton + angle sensors– AnalogousAnalogous– TetheredTethered– No identification problemNo identification problem– RealtimeRealtime– No range limitNo range limit– Rigid body approximationRigid body approximation

Jan 9Jan 9 5353

Body Tracking TechnologyBody Tracking Technology Position TrackingPosition Tracking

– Orthogonal Orthogonal Electromagnetic Electromagnetic FieldsFields

– Measurement of Measurement of Mechanical Mechanical LinkagesLinkages

– Ultrasonic SignalsUltrasonic Signals– Inertial TrackingInertial Tracking– Optical TrackingOptical Tracking

Inside Looking OutInside Looking Out Outside Looking InOutside Looking In

Angle Angle MeasurementMeasurement– Optical SensorsOptical Sensors– Strain SensorsStrain Sensors– Exoskeletal Exoskeletal

StructuresStructures– http://http://

www.measurand.cowww.measurand.com/videos/m/videos/ShapeTapeTheMoviShapeTapeTheMovie.m1ve.m1v

Jan 9Jan 9 5454

Recap Tracking TableRecap Tracking Table Focusing on Head and Hand TrackingFocusing on Head and Hand Tracking Data returned:Data returned:

– Magnetic: Magnetic: 6 DOF6 DOF– Acoustic: Acoustic: 3 DOF per sensor (need 3 to get 6 DOF)3 DOF per sensor (need 3 to get 6 DOF)– Inertial: Inertial: 3 DOF3 DOF– Optical: Optical: 6 DOF6 DOF

Spatial distortion (accuracy)Spatial distortion (accuracy)– Magnetic: Magnetic: good close to emitter, degrades quicklygood close to emitter, degrades quickly– Acoustic: Acoustic: okay close to emitterokay close to emitter– Inertial: Inertial: short time very good, poor due to driftshort time very good, poor due to drift– Optical: Optical: okay (webcam) to very good accuracyokay (webcam) to very good accuracy

ResolutionResolution– Magnetic: Magnetic: good close to emitter, degrades quicklygood close to emitter, degrades quickly– Acoustic: Acoustic: okay close to emitterokay close to emitter– Inertial: Inertial: very goodvery good– Optical: Optical: okay (webcam) to very good accuracyokay (webcam) to very good accuracy

Jitter (precision)Jitter (precision)– Magnetic: Magnetic: good close to emitter, degrades quicklygood close to emitter, degrades quickly– Acoustic: Acoustic: okay close to emitterokay close to emitter– Inertial: Inertial: lowlow– Optical: Optical: outside-looking-in vs inside-looking-out (different types of jitter). Overall pretty goodoutside-looking-in vs inside-looking-out (different types of jitter). Overall pretty good

Jan 9Jan 9 5555

Recap Tracking TableRecap Tracking Table Drift Drift

– Magnetic: Magnetic: nonenone– Acoustic: Acoustic: nonenone– Inertial: Inertial: substantialsubstantial– Optical: Optical: nonenone

Lag Lag – Magnetic: Magnetic: lowlow– Acoustic: Acoustic: moderatemoderate– Inertial: Inertial: lowlow– Optical: Optical: low to moderatelow to moderate

Update RateUpdate Rate– Magnetic: Magnetic: goodgood– Acoustic: Acoustic: poorpoor– Inertial: Inertial: goodgood– Optical: Optical: poor to very goodpoor to very good

RangeRange– Magnetic: Magnetic: 5’5’– Acoustic: Acoustic: 15’15’– Inertial: Inertial: excellentexcellent– Optical: Optical: 40’+40’+

Jan 9Jan 9 5656

Recap Tracking TableRecap Tracking Table Number of Tracked PointsNumber of Tracked Points

– Magnetic:Magnetic: 16 16– Acoustic: Acoustic: 1616– Inertial: Inertial: 11– Optical: Optical: <4<4

WirelessWireless– Magnetic:Magnetic: yes yes– Acoustic: Acoustic: yesyes– Inertial: Inertial: yesyes– Optical: Optical: yesyes

Interference and noiseInterference and noise– Magnetic:Magnetic: metal, Earth metal, Earth– Acoustic: Acoustic: environment, occlusionenvironment, occlusion– Inertial: Inertial: nonenone– Optical: Optical: occlusionocclusion

Jan 9Jan 9 5757

Recap Tracking TableRecap Tracking Table Mass, Inertia and EncumbranceMass, Inertia and Encumbrance

– Magnetic:Magnetic: low low– Acoustic: Acoustic: lowlow– Inertial: Inertial: lowlow– Optical: Optical: low to highlow to high

DurabilityDurability– Magnetic:Magnetic: high high– Acoustic: Acoustic: highhigh– Inertial: Inertial: highhigh– Optical: Optical: lowlow

PricePrice– Magnetic:Magnetic: $4000+ $4000+– Acoustic: Acoustic: $4000++$4000++– Inertial: Inertial: very cheapvery cheap– Optical: Optical: cheap (wecams) - $180k cheap (wecams) - $180k

(motion capture systems)(motion capture systems)