Towards visibility and audibility algorithms for assessing perceived safety and security in public areas based on digital 3D city models

The assessment of feeling comfortable, safe and secure versus feeling not at ease in cities is an important issue when planning to (re)design urban built environments such as public areas and residential districts. The general feeling of security in the public space is known to be related to perceived visibility and audibility. Based on digital 3D city models of existing or planned urban spaces, this paper focusses on determining visibility and audibility. Also, other potential quantities are introduced: brightness, overview, and person distribution. It presents a tentative analytical framework and algorithmic approaches expressing the relevant inputs and necessary calculation steps as well as pseudocode expressions. The paper relates the general concept of calculations involved to existing similar implementations in the literature. The proposed calculation scheme for the analysis of visibility and audibility is able to take additional factors into account, for instance exposure of persons, psychological factors, physical perception and transparency of urban furniture regarding view and sound propagation. It is able to consider psychophysical facts like decreasing of visibility and audibility with increasing distance or reflection and absorption of sound waves on urban components. The proposed approach determines visibility and audibility measures intended to be used for planning processes of safer spaces in cities.