Visibility of rectangular objects in L-1 metric

Given a set of n rectangles (2-dimensional) parallel to xy-plane, and a poi nt P(x, y, z) in 3-dimensional space, we find the visibility of all rectang les i.e., the set of all visible points of rectangles from P in L-1 metric, in O(n(4)) time and O(n(3)) space. We also discuss the cases where the poi nt P moves along a straight line and the rectangles are inserted and delete d dynamically.