Calibration and Validation of Phase One Industrial Cameras.

JOANNEUM RESEARCH has reviewed the geometric lab calibration workflow of Phase One A/S, investigating the calibration method from a theoretical point of view, but also by evaluation of an existing calibration project from their new lab in Denver, USA. In addition, two iXM-RS150F reference cameras (50mm and 150mm lens) have been calibrated in the measurement lab of the Institute of Engineering Geodesy and Measurement Systems (IGMS) at Technical University Graz, Austria and results have been compared with the Phase One calibration certificates. Although correctness and quality of the Phase One calibration workflow could be confirmed, small but significant differences exist and can only be explained using various hypothesis e.g. about the influence of different environmental conditions during calibration. As it is not possible from direct comparison to decide which parameter set is the better or even correct one, methods to validate a camera calibration in the lab have been investigated which exist e.g. for acceptance testing of 3D optical measurement systems. It was found that existing methods based on capturing dedicated test bodies using a dense photo network and comparing reconstructed 3D lengths with the calibrated ones cannot be easily transferred to aerial camera systems, especially for longer focal lengths. Therefore, a new lab validation approach has been developed and tested using more available geodetic level rods, LSM matching of the bar code and an algorithm to transfer the length measurement from the image to object space without need for standard 3D point reconstruction.