Before revision:  We further obtain} : (1) How such that \Theta}\ge to compute the O -hull of P in \Theta (n\log n) time and O(n) space, ({2} the complexities are O(\frac{n}{\Theta}\log n) time and O(\frac{n}{\Theta}) space.
After revision:  We further obtain} : (1) How such that \Theta}\ge to compute the O -hull of P in optimal O (n\log n) time and O(n) space, ({2} the complexities are O(\frac{n}{\Theta}\log n) time and O(\frac{n}{\Theta}) space.