Browsing by Author "Radovanovic, Robert"

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    Geometric modelling and calibration of a spherical camera imaging system
    (2020-04-16) Lichti, Derek D.; Jarron, David; Tredoux, Wynand; Shahbazi, Mozhdeh M.; Radovanovic, Robert
    The Ladybug5 is an integrated, multi-camera system that features a near-spherical field of view. It is commonly deployed on mobile mapping systems to collect imagery for 3D reality capture. This paper describes an approach for the geometric modelling and self-calibration of this system. The collinearity equations of the pinhole camera model are augmented with five radial lens distortion terms to correct the severe barrel distortion. Weighted relative orientation stability constraints are added to the self-calibrating bundle adjustment solution to enforce the angular and positional stability between the Ladybug5’s six cameras. Results are presented from two calibration data-sets and an independent data-set for accuracy assessment. It is demonstrated that centimetre-level 3D reconstruction accuracy can be achieved with the proposed approach. Moreover, the effectiveness of the lens distortion modelling is demonstrated. Image-space precision and object-space accuracy are improved by 92% and 93%, respectively, relative to a two-term model. The high correlations between lens distortion coefficients were not found to be detrimental to the solution. The mechanical stability of the system was assessed by comparing calibrations taken before and after ten months of routine camera system use. The results suggest sub-pixel interior orientation stability and millimetre-level relative orientation stability. Analyses of accuracy and parameter correlation demonstrate that a slightly-relaxed weighting strategy is preferred to tightly-enforced relative orientation stability constraints.
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    Improving Sidewalk Maintenance through Smartphone Citizen Reporting of Pothole Damage
    (2024-10-18) Sornsakul, Chavisa; Lichti, Derek; O'Keefe, Kyle; Radovanovic, Robert; Detchev, Ivan
    Pedestrian walkways potholes pose significant risks to pedestrian safety, causing accidents and disruptions. This thesis explores using Structure-from-Motion (SfM) 3D reconstruction with smartphone GNSS measurements to improve citizen pothole reporting, aiming to enhance local engagement, infrastructure management, and public safety. The methodology uses SfM camera poses recovered from citizen pothole image reports and relative positioning from smartphone GNSS measurements to resolve the scale ambiguity of SfM pothole models. The relationship between images and a reconstructed point cloud from the SfM technique estimates pothole quantity, perimeter, and maximum depth. Key contributions include developing an integrated system for accurate pothole dimension measurement, with a scale error of approximately 12% from reference measurements, and establishing data acquisition guidelines for assessing the reliability of citizen-reported data. This method results in pedestrian walkway pothole perimeters differing by approximately 35 cm and depths by less than 1 cm. A guide for citizens capturing pothole images is proposed.
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    Modelling Extreme Wide-Angle Lens Cameras
    (Wiley, 2021-12-01) Lichti, Derek D; Tredoux, Wynand; Maalek, Reza; Helmholz, Petra; Radovanovic, Robert
    The use of consumer cameras fitted with extreme wide angle (EWA) lenses for photogrammetric measurement is increasing. Conventional modelling of EWA systems relies on the pinhole camera model and up to five radial lens distortion terms. Aiming to reduce model complexity, this paper reports an investigation into an alternate approach using fisheye lens models for EWA systems, despite them not falling strictly into to the fisheye category. Four fisheye models were tested on four different cameras under laboratory conditions. The self-calibration results show superior model fit for all fisheye models over the pinhole plus radial model in terms of residual RMS. The number radial distortion of terms required for the fisheye models was lower in all cases, so model complexity was reduced. Independent assessment revealed very similar 3D reconstruction accuracy for all models. The results suggest that fisheye modelling is an advantageous alternative for EWA lens systems.