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Factoring in Sky View Factor

September 9, 2020

The 'Sky View Factor' (SVF) is a measure of how much sky you can see from a certain point. If you were on an infinite plane you would see a full half dome of sky. That would be 100% sky view factor.

As soon as something is placed on the infinite plane - trees, buildings, hills - parts of the sky are hidden. You can no longer see 100% of the sky: the Sky View Factor falls. The more things, the bigger and taller they are, the lower the SVF.

It is a measure for feeling enclosed, and will have an impact on the quality of open space.

It is quite easy to create the index for a point.

  1. shoot rays out from the test point
  2. check which hit geometry
  3. associate each ray with a patch of the sky dome.
  4. Work out the area of the sky that is visible from each point

To understand the sky view factor across a precinct we just run the analysis for a lot of points.

We know what the SVF is for every point. If we want higher fidelity we sample more points, if we want more speed we sample fewer. Adding a color gradient helps us understand where the lowest SVF and highest SVF areas are. Low SVF is not necessarily bad: it can mean intimate, sheltered and cosy.

Governments often want a threshold value which allows them to benchmarks precincts against a policy intent. We can add a threshold value and use it to divide the precinct into areas below, and above, the SVF threshold. This can be used to drive a pass/fail assessment criterion.

These SVF analyses are done on a simple Giraffe massing model. Adding more detailed meshes will increase the accuracy, although this SVF analysis will be close to the final result and can drive quality design from the earliest stage.

As always, this app is available on Giraffe, if you would like to run Sky View Factor analysis in minutes on proposals please contact us.