Exploring the significance of rotation angle in SVF estimate using a vector-based method

In a vector-based method for sky-view factor (SVF) calculation, selecting an appropriate rotation angle and search radius is important for accurately estimating the SVF. Researchers have used varying values for rotation angles, ranging from 1° to 22.5°. However, no rotation angle standardisation was performed. In this study, the relationship between the SVF and rotation angle was explored in an idealised symmetrical finite canyon. The SVF function in the Shadow library of R was used, with angles varying from 0.001° to 60°. The results showed that the rotation angle was not a statistically significant parameter in the SVF estimation. However, with a constant canyon length and height, the SVF increased with increasing canyon width, although with several breakpoints. Increasing the canyon length with a constant canyon height and width also resulted in breakpoints with decreasing step-widths. By varying the rotation angle, a linear pattern with breakpoints was observed at the angles obtained by dividing 360° by n, where n is an integer. The study concluded that a rotation angle that is a factor of 90° accurately estimated the SVF. Moreover, for asymmetrical canyons, rather than only lowering the rotation angles, SVF should be calculated at multiple points.