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Pinhole Camera Calibration in the Presence of Human Noise
Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The research work presented in this thesis is concerned with the analysis of the human body as a calibration platform for estimation of a pinhole camera model used in Augmented Reality environments mediated through Optical See-Through Head-Mounted Display. Since the quality of the calibration ultimately depends on a subject’s ability to construct visual alignments, the research effort is initially centered around user studies investigating human-induced noise, such as postural sway and head aiming precision. Knowledge about subject behavior is then applied to a sensitivity analysis in which simulations are used to determine the impact of user noise on camera parameter estimation.

Quantitative evaluation of the calibration procedure is challenging since the current state of the technology does not permit access to the user’s view and measurements in the image plane as seen by the user. In an attempt to circumvent this problem, researchers have previously placed a camera in the eye socket of a mannequin, and performed both calibration and evaluation using the auxiliary signal from the camera. However, such a method does not reflect the impact of human noise during the calibration stage, and the calibration is not transferable to a human as the eyepoint of the mannequin and the intended user may not coincide. The experiments performed in this thesis use human subjects for all stages of calibration and evaluation. Moreover, some of the measurable camera parameters are verified with an external reference, addressing not only calibration precision, but also accuracy.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2011. , 113 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1402
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-72055ISBN: 978-91-7393-053-6 (print)OAI: oai:DiVA.org:liu-72055DiVA: diva2:456346
Public defence
2011-11-04, Domteatern, Visualiseringscenter C, Kungsgatan 54, Norrköping, 09:30 (English)
Opponent
Supervisors
Available from: 2011-11-14 Created: 2011-11-14 Last updated: 2015-09-22Bibliographically approved
List of papers
1. User Boresighting for AR Calibration: A Preliminary Analysis
Open this publication in new window or tab >>User Boresighting for AR Calibration: A Preliminary Analysis
2008 (English)In: Proceedings of the IEEE Virtual Reality Conference 2008, IEEE , 2008, 43-46 p.Conference paper, Published paper (Refereed)
Abstract [en]

The precision with which users can maintain boresight alignment between visual targets at different depths is recorded for 24 subjects using two different boresight targets. Subjects' normal head stability is established using their Romberg coefficients. Weibull distributions are used to describe the probabilities of the magnitude of head positional errors and the three dimensional cloud of errors is displayed by orthogonal two dimensional density plots. These data will lead to an understanding of the limits of user introduced calibration error in augmented reality systems.

Place, publisher, year, edition, pages
IEEE, 2008
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-72053 (URN)10.1109/VR.2008.4480748 (DOI)978-1-4244-1971-5 (ISBN)
Conference
IEEE Virtual Reality Conference, 2008. VR '08, 8-12 March, Reno, Nevada, USA
Available from: 2011-11-14 Created: 2011-11-14 Last updated: 2011-11-21Bibliographically approved
2. User Boresight Calibration Precision for Large-Format Head-Up Displays
Open this publication in new window or tab >>User Boresight Calibration Precision for Large-Format Head-Up Displays
2008 (English)In: Proceedings of the 2008 ACM symposium on Virtual reality software and technology, New York, NY, USA: ACM , 2008, 141-148 p.Conference paper, Published paper (Refereed)
Abstract [en]

The postural sway in 24 subjects performing a boresight calibration task on a large format head-up display is studied to estimate the impact of human limits on boresight calibration precision and ultimately on static registration errors. The dependent variables, accumulated sway path and omni-directional standard deviation, are analyzed for the calibration exercise and compared against control cases where subjects are quietly standing with eyes open and eyes closed. Findings show that postural stability significantly deteriorates during boresight calibration compared to when the subject is not occupied with a visual task. Analysis over time shows that the calibration error can be reduced by 39% if calibration measurements are recorded in a three second interval at approximately 15 seconds into the calibration session as opposed to an initial reading. Furthermore parameter optimization on experiment data suggests a Weibull distribution as a possible error description and estimation for omni-directional calibration precision. This paper extends previously published preliminary analyses and the conclusions are verified with experiment data that has been corrected for subject inverted pendulum compensatory head rotation by providing a better estimate of the position of the eye. With correction the statistical findings are reinforced.

Place, publisher, year, edition, pages
New York, NY, USA: ACM, 2008
Keyword
boresight, line of sight, calibration, postural sway, augmented reality
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-43489 (URN)10.1145/1450579.1450610 (DOI)73950 (Local ID)978-1-59593-951-7 (ISBN)73950 (Archive number)73950 (OAI)
Conference
15th ACM Symposium on Virtual Reality Software and Technology, Bordeaux, France October 27-29
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2011-11-14Bibliographically approved
3. Visual Alignment Precision in Optical See - Through AR Displays: Implications for Potential Accuracy
Open this publication in new window or tab >>Visual Alignment Precision in Optical See - Through AR Displays: Implications for Potential Accuracy
2009 (English)In: Proceedings of the ACM/IEEE Virtual Reality International Conference, Association for Computing Machinery (ACM), 2009Conference paper, Published paper (Other academic)
Abstract [en]

The quality of visual registration achievable with anoptical see-through head mounted display (HMD)ultimately depends on the user’s targetingprecision. This paper presents design guidelines forcalibration procedures based on measurements ofusers’ head stability during visual alignment withreference targets. Targeting data was collected from12 standing subjects who aligned a head fixedcursor presented in a see-through HMD withbackground targets that varied in azimuth (0°, ±30°,±60°) and elevation (0°, ±10°). Their data showedthat: 1) Both position and orientation data will needto be used to establish calibrations based on nearbyreference targets since eliminating body swayeffects can improve calibration precision by a factorof 16 and eliminate apparent angular anisotropies.2) Compensation for body sway can speed thecalibration by removing the need to wait for thebody sway to abate, and 3) calibration precision canbe less than 2 arcmin even for head directionsrotated up to 60° with respect to the user’s torsoprovided body sway is corrected. Users ofAugmented Reality (AR) applications overlookinglarge distances may avoid the need to correct forbody sway by boresighting on markers at relativelylong distances, >> 10 m. These recommendationscontrast with those for heads up displays using realimages as discussed in previous papers.

Place, publisher, year, edition, pages
Association for Computing Machinery (ACM), 2009
National Category
Computer Engineering
Identifiers
urn:nbn:se:liu:diva-52848 (URN)
Conference
ACM/IEEE Virtual Reality International Conference, 2009
Available from: 2010-01-12 Created: 2010-01-12 Last updated: 2013-11-05Bibliographically approved
4. Visual Alignment Accuracy in Head Mounted Optical See-Through AR Displays: Distribution of Head Orientation Noise
Open this publication in new window or tab >>Visual Alignment Accuracy in Head Mounted Optical See-Through AR Displays: Distribution of Head Orientation Noise
2009 (English)In: Proceedings of the Human Factors and Ergonomics Society 53rd Annual Meeting 2009, San Antonio (TX), USA: Human Factors and Ergonomics Society , 2009, 2024-2028 p.Conference paper, Published paper (Refereed)
Abstract [en]

The mitigation of registration errors is a central challenge for improving the usability of AugmentedReality systems. While the technical achievements within tracking and display technology continue toimprove the conditions for good registration, little research is directed towards understanding theuser’s visual alignment performance during the calibration process. This paper reports 12 standingsubjects’ visual alignment performance using an optical see-through head mounted display for viewingdirections varied in azimuth (0°, ±30°, ±60°) and elevation (0°, ±10°). Although viewing direction hasa statistically significant effect on the shape of the distribution, the effect is small and negligible forpractical purposes and can be approximated to a circular distribution with a standard deviation of 0.2°for all viewing directions studied in this paper. In addition to quantifying head aiming accuracy with ahead fixed cursor and illustrating the deteriorating accuracy of boresight calibration with increasingviewing direction extremity, the results are applicable for filter design determining the onset and end ofhead rotation.

Place, publisher, year, edition, pages
San Antonio (TX), USA: Human Factors and Ergonomics Society, 2009
National Category
Computer Engineering
Identifiers
urn:nbn:se:liu:diva-52854 (URN)10.1177/154193120905302710 (DOI)978-161567623-1 (ISBN)
Conference
53rd Human Factors and Ergonomics Society Annual Meeting 2009, HFES 2009; San Antonio, TX; United States
Available from: 2010-01-12 Created: 2010-01-12 Last updated: 2014-09-04Bibliographically approved
5. Optical See-Through Head Mounted Display: Direct Linear Transformation Calibration Robustness in the Presence of User Alignment Noise
Open this publication in new window or tab >>Optical See-Through Head Mounted Display: Direct Linear Transformation Calibration Robustness in the Presence of User Alignment Noise
Show others...
2010 (English)In: Proceedings of the 54th Annual Meeting of the Human Factors and Ergonomics Society, 2010Conference paper, Published paper (Refereed)
Abstract [en]

The correct spatial registration between virtual and real objects in optical see-through augmented reality implies accurate estimates of the user’s eyepoint relative to the location and orientation of the display surface. A common approach is to estimate the display parameters through a calibration procedure involving a subjective alignment exercise. Human postural sway and targeting precision contribute to imprecise alignments, which in turn adversely affect the display parameter estimation resulting in registration errors between virtual and real objects. The technique commonly used has its origin incomputer vision, and calibrates stationary cameras using hundreds of correspondence points collected instantaneously in one video frame where precision is limited only by pixel quantization and image blur. Subsequently the input noise level is several order of magnitudes greater when a human operator manually collects correspondence points one by one. This paper investigates the effect of human alignment noise on view parameter estimation in an optical see-through head mounted display to determine how well astandard camera calibration method performs at greater noise levels than documented in computer vision literature. Through Monte-Carlo simulations we show that it is particularly difficult to estimate the user’s eyepoint in depth, but that a greater distribution of correspondence points in depth help mitigate the effects of human alignment noise.

Keyword
Head-mounted display, Calibration, Direct linear transform, Robustness
National Category
Control Engineering
Identifiers
urn:nbn:se:liu:diva-60435 (URN)9780945289371 (ISBN)
Conference
54th Annual Meeting of the Human Factors and Ergonomics Society, San Francisco, USA, 27 September-1 October, 2010
Available from: 2010-10-13 Created: 2010-10-13 Last updated: 2015-09-22Bibliographically approved
6. Parameter Estimation Variance of the Single Point Active Alignment Method in Optical See-Through Head Mounted Display Calibration
Open this publication in new window or tab >>Parameter Estimation Variance of the Single Point Active Alignment Method in Optical See-Through Head Mounted Display Calibration
Show others...
2011 (English)In: Proceedings of the IEEE Virtual Reality Conference / [ed] Michitaka Hirose, Benjamin Lok, Aditi Majumder and Dieter Schmalstieg, Piscataway, NJ, USA: IEEE , 2011, 27-24 p.Conference paper, Published paper (Refereed)
Abstract [en]

The parameter estimation variance of the Single Point Active Alignment Method (SPAAM) is studied through an experiment where 11 subjects are instructed to create alignments using an Optical See-Through Head Mounted Display (OSTHMD) such that three separate correspondence point distributions are acquired. Modeling the OSTHMD and the subject's dominant eye as a pinhole camera, findings show that a correspondence point distribution well distributed along the user's line of sight yields less variant parameter estimates. The estimated eye point location is studied in particular detail. Thefindings of the experiment are complemented with simulated datawhich show that image plane orientation is sensitive to the numberof correspondence points. The simulated data also illustrates someinteresting properties on the numerical stability of the calibrationproblem as a function of alignment noise, number of correspondencepoints, and correspondence point distribution.

Place, publisher, year, edition, pages
Piscataway, NJ, USA: IEEE, 2011
Series
IEEE Virtual Reality Conference, ISSN 1087-8270
Keyword
single point active alignment method, camera resectioning, calibration, optical see-through head mounted display, augmented reality
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-67233 (URN)10.1109/VR.2011.5759432 (DOI)000297260400004 ()978-1-4577-0037-8 (online), 978-1-4577-0039-2 (print) (ISBN)
Conference
IEEE Virtual Reality Conference, pages 27–34, Singapore, Republic of Singapore
Available from: 2011-04-04 Created: 2011-04-04 Last updated: 2015-09-22Bibliographically approved
7. Accuracy of Eyepoint Estimation in Optical See-Through Head-Mounted Displays Using the Single Point Active Alignment Method
Open this publication in new window or tab >>Accuracy of Eyepoint Estimation in Optical See-Through Head-Mounted Displays Using the Single Point Active Alignment Method
Show others...
2011 (English)Conference paper, Published paper (Other academic)
Abstract [en]

This paper studies the accuracy of the estimated eyepoint of an Optical See-Through Head-Mounted Display (OST HMD) calibrated using the Single Point Active Alignment Method (SPAAM). Quantitative evaluation of calibration procedures for OST HMDs is complicated as it is currently not possible to share the subject’s view. Temporarily replacing the subject’s eye with a camera during the calibration or evaluation stage has been proposed, but the uncertainty of a correct eyepoint estimation remains. In the experiment reported in this paper, subjects were used for all stages of calibration and the results were verified with a 3D measurement device. The nine participants constructed 25 visual alignments per calibration after which the estimated pinhole camera model was decomposed into its intrinsic and extrinsic parameters using two common methods. Unique to this experiment, compared to previous evaluations, is the measurement device used to cup the subject’s eyeball. It measures the eyepoint location relative to the head tracker, thereby establishing the calibration accuracy of the estimated eyepoint location. As the results on accuracy are expressed as individual pinhole camera parameters, rather than a compounded registration error, this paper complements  previously published work on parameter variance as the former denotes bias and the latter represents noise. Results indicate that the calibrated eyepoint is on average 5 cm away from its measured location and exhibits a vertical bias which potentially causes dipvergence for stereoscopic vision for objects located further away than 5.6 m. Lastly, this paper closes with a discussion on the suitability of the traditional pinhole camera model for OST HMD calibration.

Keyword
Accuracy, Single Point Active Alignment Method, Visual Alignment, Calibration, Augmented Reality
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-72054 (URN)
Conference
IEEE Virtual Reality Conference 2012, Orange County (CA), USA
Available from: 2011-11-14 Created: 2011-11-14 Last updated: 2015-09-22Bibliographically approved

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