  Motivated by the theoretical interest in reconstructing long 3D trajectories
of individual birds in large flocks, we developed CoMo, a co-moving camera
system of two synchronized high speed cameras coupled with rotational stages,
which allow us to dynamically follow the motion of a target flock. With the
rotation of the cameras we overcome the limitations of standard static systems
that restrict the duration of the collected data to the short interval of time
in which targets are in the cameras common field of view, but at the same time
we change in time the external parameters of the system, which have then to be
calibrated frame-by-frame. We address the calibration of the external
parameters measuring the position of the cameras and their three angles of yaw,
pitch and roll in the system "home" configuration (rotational stage at an angle
equal to 0deg and combining this static information with the time dependent
rotation due to the stages. We evaluate the robustness and accuracy of the
system by comparing reconstructed and measured 3D distances in what we call 3D
tests, which show a relative error of the order of 1%. The novelty of the work
presented in this paper is not only on the system itself, but also on the
approach we use in the tests, which we show to be a very powerful tool in
detecting and fixing calibration inaccuracies and that, for this reason, may be
relevant for a broad audience.
