An optimal locating-dominating set in the infinite triangular grid

Assume that G=(V,E) is an undirected graph, and C@?V. For every v@?V, we denote by I(v) the set of all elements of C that are within distance one from v. If all the sets I(v) for v@?V@?C are non-empty, and pairwise different, then C is called a locating-dominating set. The smallest possible density of a locating-dominating set in the infinite triangular grid is shown to be 1357.