Three-dimensional visibility analysis and visual quality computation for urban open spaces aided by Google SketchUp and WebGIS

Abstract

In this article, the authors has explored the feasibility of three-dimensional visibility analysis and visual quality computation via the aid of Google SketchUp and WebGIS, which may be beneficial for measurable evaluation of the environment in urban open spaces, and referential for urban planning and design to build an environment with better visual comfort. Considered for long-term significance, three-dimensional visibility analysis and visual quality computation are potential in enabling the quantitative analysis between urban open spaces and visual perception, providing appropriate standard for the evaluation of environment, and making the future planning and design rational and reasonable. Due to the easy access for entry-level programmer and the public, Google SketchUp and WebGIS were adopted as proper and efficient tools for three-dimensional visibility analysis in this research, which considerably decreased the programming development difficulty. Both SketchUp and WebGIS are thought to be well accepted by the public, as SketchUp has been popularized in three-dimensional modelling and WebGIS has been familiar as the form of websites for a long period, which may enable the dissemination of visibility analysis to the public. From a pilot study of progresses based on the past scholars’ researches, the authors developed an improved method for three-dimensional visibility analysis, by mathematically deriving the visual factors from the spatial relationship analysis of buildings, terrain and other geographical features. A few quantitative factors such as the distance, solid angle and visual field (a distribution of occupied solid angle in all directions) valued in spherical coordinate system were adopted as the basic units for visibility levels. Starting from the space prototype, the research has also focused on several aspects possibly associated with the visual effects in open spaces, including the openness, enclosure and ground coverage for edge; the distribution and dispersion for skyline and the visibility of individual building for landmark. For further comparison, the variances of those figures were also noticed during space scales changing for the prototype, in order to find possible connection or changing trend before and after. Moreover, experiments of three-dimensional visibility analysis have been designed and taken for real scenes to discover the similarities or differences between prototype and reality, and Piazza del Campo (Siena, Italy), Piazza San Marco (Venice, Italy) and Olomouc centre area (Olomouc, Czech) have been selected as the first group of candidates. Those would be the possible references for making quantitative assessments in real scenes via collection of visual factors, enabling the comparison of similarities and differences among various urban open spaces.