Sky View Factor Calculator

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Sky View Factor Calculator

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).

Location

The Sky View Factor Calculator is located at

  • UMEP
    • Pre-Processor
      • Urban Geometry
        • Sky View Factor

Running the Plugin

When you run the plugin, you will see the dialog shown below. It consists of a top section where input data is specified and a bottom section for specifying output and for running the 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 in the final SVF.

Trunk Zone DSM Exist

Tick this box if a trunk zone DSM already exist.

Transmissivity of Light Through Vegetation (%)

Percentage of light that is penetrating through vegetation. 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%.

Output Folder

A specified folder where the result will be saved.

Run

This starts the calculations.

Add Result to Project

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

Close

This button closes the plugin.

Output

Sixteen different files (geoTIFF) will be saved if vegetation DSM is used. Otherwise, five different SVFs are saved. The main one is named SkyViewFactor.tif and it shows the total SVF (i.e. the amount of sky that is seen from each pixel. The other files created are for different directions (four cardinal points) as well as SVFs divided up on various fractions such as only buildings, only vegetation etc. For a detailed description, see Lindberg and Grimmond (2011).

The figure below shows an example of input data and the resulting SVF. The left one shows a ground and building DSM (grayscale) and a DSM overlaid with a canopy DSM (yellow to green). The right shows the total SVF.

Example of input data and the resulting 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 4000000 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 Link to the paper
  • Lindberg F, Grimmond CSB (2010) Continuous sky view factor maps from high resolution urban digital elevation models. Clim Res 42:177–183 Link to the paper
  • 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 Link to the paper
  • Watson ID, Johnson GT (1987) Graphical estimation of skyview-factors in urban environments. J Climatol 7: 193–19 Link to the paper