  Monitoring the occupancy of public sports facilities is essential to assess
their use and to motivate their construction in new places. In the case of a
football field, the area to cover is large, thus several regular cameras should
be used, which makes the setup expensive and complex. As an alternative, we
developed a system that detects players from a unique cheap and wide-angle
fisheye camera assisted by a single narrow-angle thermal camera. In this work,
we train a network in a knowledge distillation approach in which the student
and the teacher have different modalities and a different view of the same
scene. In particular, we design a custom data augmentation combined with a
motion detection algorithm to handle the training in the region of the fisheye
camera not covered by the thermal one. We show that our solution is effective
in detecting players on the whole field filmed by the fisheye camera. We
evaluate it quantitatively and qualitatively in the case of an online
distillation, where the student detects players in real time while being
continuously adapted to the latest video conditions.
