A method is provided of determining the coverage of at least one optical sensor in a three dimensional (3-D) area. The 3-D area is divided into cells. The field of view of the sensor in the 3-D area is determined and rays are projected from the sensor into the 3-D area within sensor's field of view. The intersections between the rays and the cells are determined and a visual display of the 3-D area is generated showing the coverage of the sensor, based on the intersections.