Direct Radiation includes Circumsolar Radiation?


After running a single hour simulation for the direct radiation, I had a question why the result shows more than two different radiation values on my facade.
I checked with SkyDome component, and then realized that the single hour direct radiation includes more than one sun-vector or radiation value on the patched sky!

I tried to understand the python code, but failed…
Will you explain how LadyBug calculates the direct radiation on the geometry?
What is the reference for this approach?
Was it intended to simulate circumsolar radiation?
If then, what is the calculation process in LadyBug?

I attached my gh file and weather data to be selected on “file path” component.


Best regards,

Jaeman PARK (444.4 KB) (250.7 KB)

The discretized sky is based on Tregenza Sky subdivisions. . The original subdivision scheme proposed by Peter Tregenza had circular patches and therefore there were gaps in the coverage of the celestial hemisphere.

Christoph Reinhart had discussed this somewhat extensively in his dissertation work in 2000-2001. The sky dome that is implemented in Ladybug/Honeybee is based on this subdivision scheme (mostly).

No, its just solar radiation. Since the size of the patches is much larger than the size of the solar disc (which is around 0.533 steradians), it would be a gross simplification in terms of - sun position and radiant intensity - to simply assign all the radiation to single sky patch. So, the solar radiation is assigned to multiple patches instead.

Thanks sarith! Well understood!
And is it right that LadyBug uses anisotropic sky model as default (when I see the sky dome of diffuse radiation)?

For the sky domes that are generated based on radiation data and geographical variables, the model being employed is the Perez Sky Model (@mostapha would be able to confirm this). So yes, the sky is anisotropic.