# APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Vicon Calibration David Groh University of Nevada.

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APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Vicon Calibration David Groh University of Nevada – Las Vegas Department of Kinesiology

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Purpose of Calibration  To assist in the reconstruction 3D positions of captured markers from 2D camera images  To establish an absolute reference of origin and orientation

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Earlier Calibration Methods  Direct Linear Transformation (DLT) Abdel-Aziz YI and Karara HM (1971)  Non-Linear Transformation (NLT) Dapena J, Harman EA, and Miller JA (1982)

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Direct Linear Transformation  Two or more 2D views (cameras) of a control object (cube or cage) to solve for camera parameters relating the image space (external) to the object space (internal)  Both reference frame and the units of measurement are defined by the known 3- D point coordinates on the control object (Hinrichs).  Time consuming  Costly

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Non-Linear Transformation  Proposed by Dapena, et al.  Also uses control object (pole)  Specific point coordinates on the object are not necessary  Internal parameters calculated separately

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD DLT Calibration Accuracy  Chen L, et al. (1994) Five groups of control (known) points (8,12,16,20,24) >Six configurations each Results: >accuracy increased as control points increased >Best accuracy achieved with even distribution >Accuracy decreased as distance from control region increased

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD NLT vs. DLT Calibration Accuracy Hinrichs RN and McLean SP (1995)  Purpose: to compare the accuracy of the NLT vs. DLT methods To compare accuracy with and without extrapolation

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD MethodsMethods  DLT control object Cuboid, 27 strings hanging from ceiling Two defined control volumes –Entire volume (185cm x 490 cm x 213 cm) –~25% of entire volume Four groups of control points (16, 24, 40, 60)

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD MethodsMethods  NLT control volume Similar dimensions to large DLT volume Single 223cm pole with six marks >Eleven vertical positions, four horizontal positions >Encompassed the control volume  Two cameras  Mean absolute error – calculation of the resultant difference between the predicted and surveyed locations of selected points from the DLT control object (Hinrichs)

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD ResultsResults  Smallest resultant errors recorded with standard DLT re-predicting control points  Errors in re-predicting control points increased as control points increased  Errors in predicting non-control points decreased as control points increased

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD DynaCal3DynaCal3  Vicon Workstation’s current calibration method  Replaced DC2 in early 2001  Implements reconstruction algorithm  Provides System information: Positions and orientations of cameras wrt each other Focal length of lenses Lens distortion Absolute reference origin of lab

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Calibration Procedure  Dynamic calibration Wand dance Determines camera and lens variables Processed first

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Calibration Procedure  Static calibration L-frame Determines origin of lab space (absolute reference point), only Depends on successful dynamic calibration Processed last

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD DefinitionsDefinitions  Residuals – numbers that indicate the quality of calibration  Linearization – the process of correcting for lens distortion  Bundle Adjustment – an algorithm that performs the linearization process by optimizing the camera parameters to give the best re- projection error

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Dynamic Calibration  Performed first  Algorithm presumptions Known distance between wand markers No additional markers moving within the Volume during calibration 2D marker images seen by different cameras originate from the same 3D positions

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Dynamic Calibration  Algorithm first looks at camera pair with the greatest overlap.  Accumulation of additional cameras initiate optimization algorithm to determine best fit.  Bundle Adjustment performs linearization process to correct for lens distortion.

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Dynamic Calibration  Dynamic calibration algorithm uses known distance between markers to establish the scale of the volume.  This distance constant is specified in the Calibration Reference Object (CRO) file.

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Dynamic Calibration  Wand wave (“wand dance”) tips: Avoid breaking cameras’ views with one’s body. Position body so the wand can be seen by as many cameras as possible. Move around the entire volume to give all cameras an equal opportunity to see the wand wave. No need to collect more than 1000 samples

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Static Calibration  Establishes absolute spatial reference (origin)  Utilizes L-frame with two axes Tripleton – three markers Singleton – one marker

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Static Calibration  Tripleton Establishes direction of first (X) axis  Singleton Establishes position of origin Combines with the first axis to establish the second axis Resultant cross product is the third axis Origin specified in CRO file

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD ResidualsResiduals  Individual cameras A measure the accuracy of one camera with respect to all other cameras Established by reconstructing wand marker positions using all cameras except the one for which the residual is being calculated >Camera in question is non-contributory to its own 3D reconstruction residual >New with DC3

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD ResidualsResiduals  Individual cameras (cont.) The distance between the reconstructed markers image and the camera’s own image averaged across all available samples High camera residual = 2D contribution that tends to be less accurate than the other cameras

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Residuals (cont.)  Mean Residual – average of individual residuals  Residual Range – the highest and lowest residuals  Wand Visibility – the average percentage of the wand wave that contributed to each camera’s calibration  Static Reproducibility – a measure of the accuracy of the reconstructed positions of the L-frame markers as compared to the CRO file

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD Common Reasons for Failed Calibrations  Inappropriate wand wave Too fast (low frequency) Solution: slow wand wave  Poor camera positioning Inadequate overlap Solution: >adjust cameras >May need to customize wand wave  Background static noise Reposition cameras Adjust camera sensitivities (can be turned up after calibration

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD ReferencesReferences  Dapena J, Harman EA, and Miller JA. (1982) Three-dimensional cinematography with control object of unknown shape. J. Biomechanics 15:11-19  Chen L, Armstrong CW, and Raftopoulos DD. (1994) An investigation on the accuracy of three-dimensional space reconstruction using the direct linear transformation technique. J. Biomechanics 27:493-500

APA 6905 INSTRUMENTATION FOR RESEARCH IN MOVEMENT SCIENCE SCHOOL OF HUMAN KINETICS Mario Lamontagne PhD ReferencesReferences  Hinrichs RN, McLean SP. (1995) NLT and extrapolated DLT: 3-D cinematography alternatives for enlarging the volume of calibration. J. Biomechanics 28:1219-1223

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