  In robotics, accurate ground-truth position fostered the development of
mapping and localization algorithms through the creation of cornerstone
datasets. In outdoor environments and over long distances, total stations are
the most accurate and precise measurement instruments for this purpose. Most
total station-based systems in the literature are limited to three Degrees Of
Freedoms (DOFs), due to the use of a single-prism tracking approach. In this
paper, we present preliminary work on measuring a full pose of a vehicle,
bringing the referencing system to six DOFs. Three total stations are used to
track in real time three prisms attached to a target platform. We describe the
structure of the referencing system and the protocol for acquiring the ground
truth with this system. We evaluated its precision in a variety of different
outdoor environments, ranging from open-sky to forest trails, and compare this
system with another popular source of reference position, the Real Time
Kinematics (RTK) positioning solution. Results show that our approach is the
most precise, reaching an average positional error of 10 mm and 0.6 deg. This
difference in performance was particularly stark in environments where Global
Navigation Satellite System (GNSS) signals can be weaker due to overreaching
vegetation.
