  Arbitrary Pattern Formation is a widely studied problem in autonomous robot
systems. The problem asks to design a distributed algorithm that moves a team
of autonomous, anonymous and identical mobile robots to form any arbitrary
pattern given as input. The majority of the existing literature investigates
this problem for robots with unobstructed visibility. In a few recent works,
the problem has been studied in the obstructed visibility model, where the view
of a robot can be obstructed by the presence of other robots. However, in these
works, the robots have been modelled as dimensionless points in the plane. In
this paper, we have considered the problem in the more realistic setting where
the robots have a physical extent. In particular, the robots are modelled as
opaque disks. Furthermore, the robots operate under a fully asynchronous
scheduler. They do not have access to any global coordinate system, but agree
on the direction and orientation of one coordinate axis. Each robot is equipped
with an externally visible light which can assume a constant number of
predefined colors. In this setting, we have given a complete characterization
of initial configurations from where any arbitrary pattern can be formed by a
deterministic distributed algorithm.
