A method and system for defining a horizon on the surface with reference to the observation point, and identifying a region within the space that is beneath the horizon. Identifying a region that is beneath the horizon includes projecting a ray from the observation point that intersects the horizon and defines an area that is occluded from the observation point. The method and system may also include determining the depth of the region that is beneath the horizon and disregarding this region when the depth is less than a predetermined threshold. In addition, the method and system may identify a region within the space that is beyond the horizon.