  The KM3NeT collaboration is constructing two large neutrino detectors in the
Mediterranean Sea: ARCA, located near Sicily and aiming at neutrino astronomy,
and ORCA, located near Toulon and designed for neutrino oscillation studies.
The two detectors, together, will have hundreds of Detection Units (DUs) with
18 Digital Optical Modules (DOMs) maintained vertical by buoyancy, forming a
large 3D optical array for detecting the Cherenkov light produced after the
neutrino interactions. To properly reconstruct the direction of the incoming
neutrino, the position of the DOMs must be known precisely with an accuracy of
less than 10 cm. For this purpose, there are acoustic and orientation sensors
inside the DOMs. An Attitude Heading Reference System (AHRS) chip provides the
components values of the Acceleration and Magnetic field in the DOM, from which
it is possible to calculate Yaw, Pitch, and Roll for each floor of the line. A
piezo sensor detects the signals from fixed acoustic emitters on the seafloor,
so as to position it by trilateration. Data from these sensors are used as an
input to reconstruct the shape of the entire line based on a DU Line Fit
mechanical model. This proceeding presents an overview of the KM3NeT monitoring
system, as well as the line fit model and a selection of results.
