INTRODUCTION AND VALIDATION OF A NOVEL CALIBRATION FRAME

The use of Photogrammetry is increasingly used by several disciplines, including marine science. Among others, the accuracy of a 3D model generated from images, depends on the quality of the calibration and stability of the camera used to capture the images. For the calibration an optimum 3D geometry is essential to minimise correlations between the camera’s interior orientation parameters. For the calibration, usually various different types of calibration frames are used. However, in practice, it can be challenging to use these frames when working in underwater environments. Calibration frames can be bulky, which makes them difficult to handle and transport, especially in boats where space is at a premium. This study aimed to develop a collapsible (and thereby portable) calibration frame, which is more practical for marine field data capture. The proposed collapsible calibration frame is validated in-air and underwater. Overall, three tests are performed. Firstly, the reliability of the frame is validated, i.e. if the collapsible frame can be put together in such a way that the Ground Control Points (GCPs) on the frame have unchanged positions relative to each other. The test showed a very small bias which could be removed by changing to a baseline assessment. Secondly, repeatability is validated, i.e. if the same results can be achieved for different software and camera combinations when using the same baselines. The test showed a clear downwards trend of the results for lower-grad cameras. However, all adjustments using the different software solutions and cameras show that the frame is suitable for application in-air. The final test is an underwater performance test which verified that the frame is usable achieving root-mean-squared error values of below 2 mm when using baselines.