  In the context of robotics, accurate ground-truth positioning is the
cornerstone for the development of mapping and localization algorithms. In
outdoor environments and over long distances, total stations provide accurate
and precise measurements, that are unaffected by the usual factors that
deteriorate the accuracy of Global Navigation Satellite System (GNSS). While a
single robotic total station can track the position of a target in three
Degrees Of Freedom (DOF), three robotic total stations and three targets are
necessary to yield the full six DOF pose reference. Since it is crucial to
express the position of targets in a common coordinate frame, we present a
novel extrinsic calibration method of multiple robotic total stations with
field deployment in mind. The proposed method does not require the manual
collection of ground control points during the system setup, nor does it
require tedious synchronous measurement on each robotic total station. Based on
extensive experimental work, we compare our approach to the classical extrinsic
calibration methods used in geomatics for surveying and demonstrate that our
approach brings substantial time savings during the deployment. Tested on more
than 30 km of trajectories, our new method increases the precision of the
extrinsic calibration by 25 % compared to the best state-of-the-art method,
which is the one taking manually static ground control points.
