Spatial calibration of large volume photogrammetry based metrology systems

Abstract

Photogrammetry systems are used extensively as volumetric measurement tools in a diverse range of applications including gait analysis, robotics and computer generated animation. For precision applications the spatial inaccuracies of these systems are of interest. In this paper, an experimental characterisation of a six camera Vicon T160 photogrammetry system using a high accuracy laser tracker is presented. The study was motivated by empirical observations of the accuracy of the photogrammetry system varying as a function of location within a measurement volume of approximately 100 m3. Error quantification was implemented through simultaneously tracking a target scanned through a sub-volume (27 m3) using both systems. The position of the target was measured at each point of a grid in four planes at different heights. In addition, the effect of the use of passive and active calibration artefacts upon system accuracy was investigated. A convex surface was obtained when considering error as a function of position for a fixed height setting confirming the empirical observations when using either calibration artefact. Average errors of 1.48 mm and 3.95 mm were obtained for the active and passive calibration artefacts respectively. However, it was found that through estimating and applying an unknown scale factor relating measurements, the overall accuracy could be improved with average errors reducing to 0.51 mm and 0.59 mm for the active and passive datasets respectively. The precision in the measurements was found to be less than 10 μm for each axis

Breast Cancer: Model Reconstruction and Image Registration From Segmented Deformed Image Using Visual and Force Based Analysis

“…A continuous scan is carried out across the surface of the breast phantom and the scanning path is recorded using a VICON camera tracking system. Here the VICON is constructed using twelve cameras and can measure a global position and orientation with six degree freedom with ≈0.5mm position accuracy [36]. The material of the phantom is very soft (like the breast), so very little pressure will change the surface and stretch the vein pattern like in the real scenario.…”

“…T otal error T otal distance travelled (18) The total error in time of scanning with respect to the increment of image sequence is shown in Fig. 14. The error is calculated by measuring the linear distance from the VICON [36] position and estimated position in each schemes. The error in the camera position is occur due to the stretching deformation.…”

Functional strength training and movement performance therapy produce analogous improvement in sit-to-stand early after stroke: early-phase randomised controlled trial

“…Reflective markers were attached to each body segment (head/trunk/arms/hands/thighs/lower legs/feet), and tracked with a three-dimensional motion capture system (Vicon, Oxford Metrics, Oxford, UK) which has reported accuracy <0.6 mm [14], intrarater reliability >0.8 (ICC) [15] and a standard error of measurement <5° [15]. The participant's feet were placed on separate forceplates to record ground reaction forces throughout the movement.…”

Comparative Performance between Two Photogrammetric Systems and a Reference Laser Tracker Network for Large‐Volume Industrial Measurement

“…The measurement uncertainty is determined by using a method of coordinate comparison. The reference network provides a coordinate definition (determination of the parameters defining the X , Y , Z system used) with a known measurement uncertainty, improving on the use of a single laser tracker as a reference standard (Summan et al., ).…”

“…The measurement uncertainty is determined by using a method of coordinate comparison. The reference network provides a coordinate definition (determination of the parameters defining the X, Y, Z system used) with a known measurement uncertainty, improving on the use of a single laser tracker as a reference standard (Summan et al, 2015). The uncertainty estimates for the two photogrammetric systems are compared to a single-station laser tracker measurement, utilised in manufacturing applications, as a performance benchmark.…”