Can 3d visibility calculations along a path predict the perceived density of participants immersed in a virtual reality environment?

The wellbeing of pedestrians in an urban setting is central concern in the dense urban context for both current and future cities. A sense of crowdedness may greatly influence the public's physical and mental health. Urban centres attract a large concentration of pedestrians and the perception of crowdedness may affect human comfort and even interfere with activity. Structural 3D morphology and additional elements that make up the visible environment, such as vegetation and exposure to a view of the sky influence perception along a pedestrian path. Walking in the centre of a broad boulevard shaded with trees and surrounded by4-6 story buildings would be perceived differently than walking along a side walk adjacent to very tall buildings. Recently, many intense studies have been examining walkability, wayfinding, human cognition and decision-making along pedestrian paths in the urban environment. At the same time, several spatial modelling and analysis tools have been developed to represent and explain variant phenomenon in this complex environment; amongst them models focusing on 3D visual analysis and its relation to human perception. 3D LOS visibility analysis has been found to be an accurate indicator of perceived density experienced by participants in various studies. In this paper we will present a dynamic LOS 3D visibility analysis for pedestrian paths examining variant layers of visual information including building structure, streets, trees and the afforded view of the sky. A virtual model of the environment was developed using Grasshopper and Rhinoceros software. The model allows for variations of the same path to be examined with several different parameters such as height of buildings, orientation of path, location of path (middle of boulevard or side walk) and the presence or lack of trees. The dynamic movement of walking an urban path was then represented as the accumulated visibility calculations of the viewpoints along that path directed towards a static target point. Model calculations were assessed by way of an extensive experiment in a visualization lab where participants were immersed in virtual reality environments. Participants were asked to imagine they are walking down a main street in a city, towards the end of the street while on their way somewhere. Participants were asked to record their perception of density for each path. The estimate ranged from 1 (not dense at all) to 7 (very dense). The difference in the evaluations between paths was compared to the variance between visibility calculations in the same respective paths. This 3D visibility model may become an essential tool in the planning and design of public spaces in existing and future cities.