The traditional distributed model of autonomous, homogeneous, mobile point robots usually assumes that the robots do not create any visual obstruction for the other robots, i.e., the robots are see through. In this paper, we consider a slightly more realistic model, by incorporating the notion of obstructed visibility (i.e., robots are not see through) for other robots. Under the new model of visibility, a robot may not have the full view of its surroundings. Many of the existing algorithms demand that each robot should have the complete knowledge of the positions of other robots. Since, vision is the only mean of their communication, it is required that the robots are in general position (i.e., no three robots are collinear). We consider asynchronous robots. They also do not have common chirality (or any agreement on a global coordinate system). In this paper, we present a distributed algorithm for obtaining a general position for the robots in finite time from any arbitrary configuration. The algorithm also assures collision free motion for each robot. This algorithm may also be used as a preprocessing module for many other subsequent tasks performed by the robots.

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This paper proposes a deterministic gathering algorithm for n ≥ 5 autonomous, homogeneous, asynchronous, oblivious unit disc robots (fat robots). The robots do not have common coordinate system and chirality. A robot can sense or observe its surroundings by collecting information about the positions of all the robots. Based on this information, they compute their destinations for moving and move there. Initially, the robots are stationary and separated. Robots are assumed to be transparent but solid. The algorithm for gathering is designed in such a way that the robots do not collide. In order to avoid collision we do not allow all the robots to move at a time. A unique robot, called leader is elected to move to its destination. No other robot moves till the leader reaches its destination. When the leader reaches its destination, another leader is selected from the remaining robots. However, leader election may not be possible in an arbitrary configuration. In this paper, we characterize all geometric configurations where leader election is possible and present an algorithm for leader election in such a case. An important property of our leader election algorithm is that it is possible to elect a leader from the remaining set of robots also.

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