Before revision:  In another research, the visibility area of a point be computed in O(} n ) time , where r denotes the cardinality of reflex vertices of \({\mathcal {P}\) }   in the output.
After revision:  In another research, the visibility area of a point be computed in O(} n ) time , where r denotes the cardinality of reflex vertices of \({\mathcal {P}\) } \mathcal in the output.