Copyright, 1999 © Valerie A. Summers

Calibration for Augmented Calibration for Augmented Reality Experimental Reality Experimental TestbedsTestbeds

VHL

Valerie A. Summers

Computer Science

U. of British Columbia

Tom Calvert

Computer Science

TechBC

Evan Graham

DSI DatoTech Systems Inc.

Christine L. MacKenzie

Kinesiology

Simon Fraser University

Kellogg S. Booth

Computer Science

U. of British Columbia

OverviewOverview

• The ProblemThe Problem

• Physical ConfigurationPhysical Configuration

• Workspace CalibrationWorkspace Calibration

• Point of View CalibrationPoint of View Calibration

• Physical Object CalibrationPhysical Object Calibration

• Discussion and Previous WorkDiscussion and Previous Work

The ProblemThe Problem

• Accurate registration between real and virtual Accurate registration between real and virtual objects is hard: “Current AR systems cannot objects is hard: “Current AR systems cannot convincingly meet this requirement. Typically convincingly meet this requirement. Typically a virtual object appears to swim about as the a virtual object appears to swim about as the user moves…’’ (State, 1996)user moves…’’ (State, 1996)

• We do not fully understand how calibration We do not fully understand how calibration errors affect human performanceerrors affect human performance

• Calibration of a kinematic testbed has Calibration of a kinematic testbed has requirements not found in other applicationsrequirements not found in other applications

Benefits of Kinematic ExperimentsBenefits of Kinematic Experiments

• Designers of AR systems can predict task Designers of AR systems can predict task error based on varying levels of calibration error based on varying levels of calibration accuracyaccuracy

• Increased knowledge of basic human Increased knowledge of basic human interaction in augmented environmentsinteraction in augmented environments

GoalsGoals

• Identify calibration requirements of an Identify calibration requirements of an experimental AR systemexperimental AR system

• Merge these requirements with traditional Merge these requirements with traditional calibration requirementscalibration requirements

• Provide techniques which satisfy both sets of Provide techniques which satisfy both sets of requirements simultaneouslyrequirements simultaneously

Calibration RequirementsCalibration Requirements

Traditional RequirementsTraditional Requirements

““Ideally, the calibration methods should be statistically Ideally, the calibration methods should be statistically robustrobust, , there should be a there should be a variety of approachesvariety of approaches for different for different circumstances, and metrology equipment should be sufficiently circumstances, and metrology equipment should be sufficiently accurateaccurate, , convenientconvenient to use, and to use, and not too expensivenot too expensive”. ”. (Hollerbach and Wampler, 1996)(Hollerbach and Wampler, 1996)

Additional Requirements of Experimental Subsystems:Additional Requirements of Experimental Subsystems:

•independentindependent (not rely on each other) (not rely on each other)

•subject-specificsubject-specific (account for individual differences) (account for individual differences)

•avoid residual cuesavoid residual cues (to prevent subjects using them in (to prevent subjects using them in unanticipated ways)unanticipated ways)

Physical ConfigurationPhysical Configuration

Stereo images Stereo images

• drawn on drawn on monitormonitor

• reflect in mirrorreflect in mirror

• appear appear between between desktop and desktop and mirrormirror

Calibration ComponentsCalibration Components

• workspaceworkspace

• point of viewpoint of view

• physical objectsphysical objects

Workspace CalibrationWorkspace Calibration

• Markers are Markers are aligned with virtual aligned with virtual crosses crosses

• Exactly one Exactly one position in 3-space position in 3-space eliminates “swim”eliminates “swim”

• do NOT need do NOT need stereo to calibratestereo to calibrate

Workspace Calibration EvaluationWorkspace Calibration Evaluation

Maximum variation for any marker (mm)Maximum variation for any marker (mm)

• 1.49 (X), 1.02 (Y), 1.34 (Z)1.49 (X), 1.02 (Y), 1.34 (Z)

Errors in workspace calibrationErrors in workspace calibration

• affect placement of virtual objects relative to affect placement of virtual objects relative to workspaceworkspace

• do do notnot affect relative distance and location of virtual affect relative distance and location of virtual objectsobjects

• do do notnot affect placement of augmented objects (errors affect placement of augmented objects (errors cancel)cancel)

Point of View CalibrationPoint of View Calibration

Subject Subject placing eye placing eye calibration calibration barsbars

POV -- Parameter IndependencePOV -- Parameter Independence

• Interpupillary distance correctly computed Interpupillary distance correctly computed for for eacheach subject subject

• Does Does notnot assume this distance is evenly assume this distance is evenly divided by nose piecedivided by nose piece

• Vertical placement of POV need Vertical placement of POV need notnot be be be be center of glassescenter of glasses

• Glasses need Glasses need notnot sit levelly on head sit levelly on head

Comparison of Calibration and Comparison of Calibration and Pupillometer ReadingsPupillometer Readings

• Interpupillary distances (IPDs) measured for Interpupillary distances (IPDs) measured for 3 subjects3 subjects

• Optician’s pupillometer measured IPDs over Optician’s pupillometer measured IPDs over focal lengths ranging from 35 cm to infinityfocal lengths ranging from 35 cm to infinity

• IPDs obtained via calibration technique were IPDs obtained via calibration technique were within pupillometer rangewithin pupillometer range

Effect of Eye Calibration on Effect of Eye Calibration on PerceptionPerception

Mean Error (mm)Mean Error (mm)

XX Y Y Z Z

1.31.3 0.50.5 1.71.7

Max Error (mm)Max Error (mm)

XX Y Y Z Z

33 1 1 4 4

Physical Object CalibrationPhysical Object Calibration

• Markers Markers placed placed anywhere anywhere on objecton object

• Place object Place object in frame so in frame so XYZ XYZ orientations orientations matchmatch

Object Calibration -- Sources of ErrorObject Calibration -- Sources of Error

• tracking error (0.3 mm)tracking error (0.3 mm)

• physical measurement of object with ruler physical measurement of object with ruler (< 1 mm)(< 1 mm)

• positioning errors (negligible)positioning errors (negligible)

Combined CalibrationsCombined Calibrations

Stereo image (2 viewpoints) of a physical block augmented with a virtual wire frame

•Workspace, point of view and objects can be calibrated in any order

•Can re-calibrate any component without affecting others

•Transformations combined off-line for performance prior to real-time execution

Coordinate System TransformationsCoordinate System Transformations

EvaluationEvaluation

• robustrobust

• flexibleflexible

• accurateaccurate

• convenient to useconvenient to use

• affordableaffordable

… … Plus ...Plus ...

• independentindependent

• subject-specificsubject-specific

• avoid extraneous cuesavoid extraneous cues

Previous WorkPrevious Work

Experimental Virtual Environment TestbedsExperimental Virtual Environment Testbeds

• VRMAT (Pouprev et al., 1997)VRMAT (Pouprev et al., 1997)

• VEPAB (Lampton et al., 1994)VEPAB (Lampton et al., 1994)

Augmented Reality CalibrationAugmented Reality Calibration

• magnetic tracker calibration (Ghazisaedy et al., 1995)magnetic tracker calibration (Ghazisaedy et al., 1995)

• optical see-through HMDs (Azuma and Bishop, 1994)optical see-through HMDs (Azuma and Bishop, 1994)

• hybrid tracking systems (State et al., 1996)hybrid tracking systems (State et al., 1996)

• monitor based augmented reality(Tuceryan et al., 1995)monitor based augmented reality(Tuceryan et al., 1995)

ConclusionsConclusions

• Calibration of experimental systems have Calibration of experimental systems have requirements beyond those of other applications requirements beyond those of other applications (independent, subject-specific, eliminate extraneous (independent, subject-specific, eliminate extraneous cues)cues)

• Can achieve experimental and traditional calibration Can achieve experimental and traditional calibration requirements simultaneouslyrequirements simultaneously

• Independence requirement benefits non-experimental Independence requirement benefits non-experimental systemssystems

• These techniques are in production use by kinesiology These techniques are in production use by kinesiology researchersresearchers

Financial SupportFinancial Support

• Natural Sciences and Engineering Research Natural Sciences and Engineering Research Council of CanadaCouncil of Canada

• Media and Graphics Interdisciplinary Centre Media and Graphics Interdisciplinary Centre at UBCat UBC

• Simon Fraser UniversitySimon Fraser University

• BC Advanced Systems InstituteBC Advanced Systems Institute

Physical ConfigurationPhysical Configuration

Workspace CalibrationWorkspace Calibration

Point of View CalibrationPoint of View Calibration

Physical Object CalibrationPhysical Object Calibration

Physical objects are placed in the corner of the frame for calibration