Koltun, VladlenCohen-Or, Daniel2015-11-112015-11-1120001017-4656https://doi.org/10.2312/egs.20001009This paper deals with the problem of identifying effective occluders for visibility culling. The solid-angle metric is commonly used for measuring the potential significance of occluders from a single viewpoint. In this paper, we show that it does not extend properly to from-region occlusion calculations. We propose to measure the effectiveness of an occluder by means of the size of its umbra. We first present an analytic object-space algorithm to accurately compute this measure. We then define an approximation which reflects the effectiveness of an occluder, and introduce a hardware-assisted algorithm to rapidly compute it.