Traditional coarse pointing, acquisition, and tracking (CPAT) systems are pre-calibrated to have the center pixel
of the camera aligned to the laser pointing vector and the center pixel is manually moved to the target of interest
to complete the alignment process. Such a system has previously demonstrated its capability in aligning with
distant targets and the pointing accuracy is on the order of sensor resolution. However, aligning with targets at
medium range where the distance between angular sensor and transceiver is not negligible is its Achilles Heel.
This limitation can be resolved by imposing constraints, such as the trifocal tensor (TT), which is deduced from
the geometrical dependence between cameras and transceivers.
Two autonomous CPAT systems are introduced for FSO transceiver alignment in mid- and long-range scenarios.
This work focuses on experimental results that validate the pointing performance for targets at different
distances, backed up by the theoretical derivations. A mid-range CPAT system, applying a trifocal tensor as its
geometric invariant, includes two perspective cameras as sensors to perceive target distances. The long-range
CPAT system, applying linear mapping as the invariant, requires only one camera to determine the pointing
angle. Calibration procedures for both systems are robust to measurement noise and the resulting system can
autonomously point to a target of interest with a high accuracy, which is also on the order of sensor resolution.
The results of this work are not only beneficial to the design of CPAT systems for FSO transceiver alignment,
but also in new applications such as surveillance and navigation.