Standard Operating Procedure for Flat Port Camera Calibration. Version 0.2.

Abstract

This document specifies the practical procedure to obtain good images for geometric camera calibration at GEOMAR. Geometric camera calibration means that for each pixel in the image the associated 3D ray in space is known with respect to the camera. This is useful for measuring with cameras, i.e. to reason about sizes, distances, angles, volumes, surfaces in 2D and 3D and to track the motion of a camera through space. This document is the first SOP for calibration and refers to the intrinsic, geometric calibration of a single camera with at port interface that is submerged underwater, in particular how to capture the calibration data. Photometric calibration (intensities, colours) of camera, light and water properties is out of scope of this document and also geometric calibration of dome ports, stereo systems, camera-laser calibration or so called handy-eye calibration of a camera and a platform (e.g. ROV) or other sensors, has to be specified in further documents. Still, the principles about image capture, image quality and so on, carry on to other calibration tasks as well. In a first step the classical intrinsic camera calibration is performed in air to obtain the exact focal length and other lens parameters. Ideally, in a second step the camera is submerged underwater to obtain the refractive calibration, i.e. parameters such as at port interface normal, thickness and distance. All images must be captured with the same zoom1 and focus2 setting.