3.8. Urban Geometry: Sky View Factor Calculator

  • Contributor
    Name Institution
    Fredrik Lindberg Gothenburg
    Sue Grimmond Reading
  • Introduction

    The Sky View Factor plugin can be used to generate pixel wise sky view factor (SVF) using ground and building digital surface models (DSM). Optionally, vegetation DSMs could also be used. By definition, SVF is the ratio of the radiation received (or emitted) by a planar surface to the radiation emitted (or received) by the entire hemispheric environment (Watson and Johnson 1987). It is a dimensionless measure between zero and one, representing totally obstructed and free spaces, respectively. The methodology that is used to generate SVF here is described in Lindberg and Grimmond (2010).

  • Dialog box

    Fig. 3.22 The dialog for the Sky View Factor calculator

  • Dialog sections
    top Specify input data
    middle Use new option (faster) to be used with SOLWEIG>v2019a
    bottom Specify output data and run calculation
  • Building and Ground DSM

    A DSM (geoTIFF) consisting of ground and building heights.

  • Vegetation Canopy DSM

    A DSM (geoTIFF) consisting of pixels with vegetation heights above ground. Pixels where no vegetation is present should be set to zero.

  • Vegetation Trunk Zone DSM

    A DSM (geoTIFF) consisting of pixels with vegetation trunk zone heights above ground. Pixels where no vegetation is present should be set to zero.

  • Use Vegetation DSMs

    Tick this box if you want to include vegetation (trees and bushes) in the final SVF.

  • Trunk Zone DSM Exist

    Tick this box if a trunk zone DSM already exists.

  • Transmissivity of Light Through Vegetation (%)

    Percentage of light that is penetrating through vegetation. The default value is set to 3 % according to Konarska et al. (2013).

  • Percentage of Canopy height

    If a trunk zone vegetation DSM is absent, this can be generated based on the height of the Canopy DSM. The default percentage is set to 25%.

  • Use method with 145 shadow images instead of 655 (required for anisotrophic sky SOLWEIG>v2019a

    If ticked, the model only interates 145 times instead of 655. This produce almost identical SVF images but is about three times faster.

  • Output Folder

    Specify folder where results will be saved.

  • Run

    Starts the calculations.

  • Add Result to Project:

    If ticked, the total SVF raster will be added to the map canvas.

  • Close

    Closes the plugin.

  • Output

    16 files (geoTIFF) will be saved if vegetation DSM is used. Otherwise, 5 SVFs are saved. If the option using 145 patches is tick in, a *.npz is also written to disk. This file can later be used in the (SOLWEIG model).

File Description
SkyViewFactor.tif Total SVF, i.e. amount of sky that is seen from each pixel.
SVF different directions Four cardinal points
SVF based on various fractions Only buildings, only vegetation etc. For a detailed description, see Lindberg and Grimmond (2011).
  • Example

    Fig. 3.23 Example of (left) input data - ground and building DSM (grayscale), DSM overlaid with a canopy DSM (yellow to green). Right: the resulting SVF -light highest SVF

  • Remarks
    • All DSMs need to have the same extent and pixel size.
    • This plugin is computationally intensive i.e. large grids will take a lot of time and very large grids will not be possible to use. Large grids e.g. larger than 4,000,000 pixels should be tiled before.
  • References
    • Konarska J, Lindberg F, Larsson A, Thorsson S, Holmer B (2013). Transmissivity of solar radiation through crowns of single urban trees—application for outdoor thermal comfort modelling. Theoret. Appl. Climatol., 1–14
    • Lindberg F, Grimmond CSB (2010) Continuous sky view factor maps from high resolution urban digital elevation models. Clim Res 42:177–183
    • Lindberg, F., Grimmond, C.S.B., 2011a. The influence of vegetation and building morphology on shadow patterns and mean radiant temperatures in urban areas: model development and evaluation. Theoret. Appl. Climatol. 105, 311–323
    • Watson ID, Johnson GT (1987) Graphical estimation of skyview-factors in urban environments. J Climatol 7: 193–197