QuVue

The view to the outside through a window is an important factor for occupants in high density high-rise urban environments. Good views have a positive relationship with occupants’ health [28] and productivity [29], and real estate values [30]. In highly dense urban environments, it is important to consider the quantitative aspect of view, due to the lack of attractive scenery and access to the sky [31]. Generally, the quantitative value of view can be measured as the visible sky ratio, which is significantly affected by the arrangement of surrounding obstructions [1]. The amount of visible sky is highly correlated to daylighting availability, and thus is prescribed by building regulations. However, the detailed requirements have been less frequently discussed than solar access [31]. Thus, in terms of a performance-based building design process, view analysis should be integrated at the early design stages of site planning in order to provide architects with well-defined information and flexibility in the subsequent design phases, and ultimately improve occupant satisfaction.

The authors’ previous research on this topic categorized the evaluation methods of quantitative visible sky into three different approaches: 1) 2D projection, 2) 3D sky segmentation, and 3) DF-based methods [14]. The major limitations of these methods include: 1) inaccuracy originating from distortion during the 2D projection process, 2) an inability to include the downward view via spherical ray-tracing, and 3) a dependency upon the sky model, geographical location, orientation of observation surface, the sun’s position, and material properties and form of the surroundings (see Table 1 and Fig. 2). To overcome these limitations, uVSF was developed to calculate the visible sky ratio, using a computational numerical model. The uVSF algorithm generates a set of boundary surfaces to enclose an obstructing building by tracing the vertexes of the surrounding buildings, and creates intersection curves between the hemisphere and boundary surface to calculate the visible sky area. The main strength of the algorithm is that it projects the obstacles onto the 3D hemisphere without distortion and prevents the loss of downward view at the high-level test points; this algorithm can potentially be used in practice, regardless of any complexities accompanying obstacles, layouts, orientations, and heights (see Fig. 3). The detailed process for the uVSF algorithm can be found in the authors’ previous work [14].

Table 1. Quantitative visible sky ratio evaluation methods and their limitations.

Category	Visible sky ratio evaluation method	Limitation
2D projection	Waldram diagrams [32]	Distortions and exaggerations during the 2D projection
2D projection	2D Isovist fields [33]	Street-level open view (2D horizontal view)
3D sky segmentation	Sky View Factor (SVF) [34]	Different weighted factors for the radiative flux density from different solar angles
	Sky Exposure Factor (SkyEF) [35]	Unable to include human perception at upper floors and on sloped surfaces
	Spatial Openness Index (SOI) [36]	Volumetric space measurement (perceived density)
DF-based estimation	Vertical Daylighting Factor (VDF) [22]	Results dependent on the sky model, location, orientation, sun’s position, height of measurement, and material properties of the surroundings
	Vertical Sky Component (VSC) [22]
	Unobstructed Vision Area (UVA) [7]
	Visual Sky Area (VSA) [2]
	Sky Solid Angle (SSA) [37]

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QuVue: A tool for uVSF(SkyView Ratio) Analysis

What is QuVue ?*