Gathering on an Infinite Triangular Grid with Limited Visibility

This work deals with the problem of gathering of $n$ oblivious mobile entities, called robots, with limited visibility, at a point (not known beforehand) placed on an infinite triangular grid. Earlier works of gathering mostly considered the robots either on a plane or on a circle or on a rectangular grid under both full and limited visibility. In the triangular grid, there are two works to the best of our knowledge. The first one is arbitrary pattern formation where full visibility is considered (\cite{C21}). The other one considers seven robots with 2- hop visibility that form a hexagon with one robot in the center of the hexagon in a collision-less environment under a fully synchronous scheduler (\cite{ShibataOS00K21}). In this work, we first show that gathering on a triangular grid with 1-hop vision of robots is not possible even under a fully synchronous scheduler if the robots do not agree on any axes. So one axis agreement has been considered in this work (i.e., the robots agree on a direction and its orientation). With this capability of robots, this work shows that a swarm of any number of robots with 1-hop visibility can gather within a finite time even when the scheduler is semi-synchronous.