  In order to advance underwater computer vision and robotics from lab
environments and clear water scenarios to the deep dark ocean or murky coastal
waters, representative benchmarks and realistic datasets with ground truth
information are required. In particular, determining the camera pose is
essential for many underwater robotic or photogrammetric applications and known
ground truth is mandatory to evaluate the performance of e.g., simultaneous
localization and mapping approaches in such extreme environments. This paper
presents the conception, calibration and implementation of an external
reference system for determining the underwater camera pose in real-time. The
approach, based on an HTC Vive tracking system in air, calculates the
underwater camera pose by fusing the poses of two controllers tracked above the
water surface of a tank. It is shown that the mean deviation of this approach
to an optical marker based reference in air is less than 3 mm and 0.3 deg.
Finally, the usability of the system for underwater applications is
demonstrated.
