Ladybug Sky Mask and the Sky Density Factor

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Hello Ladybuggers

I need to confirm what the total sky dome patches are for the density inputs 1 through to 6 for the LB Sky Mask component in 1.3 and also 0.6.8.

My understanding is based on the following:

  1. From the Primer here: Shading_Mask · Ladybug Primer it indicates that 0 = 145 however in LB 1.3 asks for integers greater or equal to 1.

  2. Also from the primer here GenCumulativeSkyMtx · Ladybug Primer and assuming the density input follows the logic of the skydensity input of the GenCumulativeSkyMtx:

     0 = 145
 1 = 580

  3. Following the link over to Radiance and GenDayMtx here http://www.radiance-online.org/learning/documentation/manual-pages/pdfs/gendaymtx.pdf suggests:

     0 = 145
 4 = 2305

  4. Radiance uses the Reinhart patch subdivision which is also discussed in the LB Primer documentation. So after a bit of digging I found this paper: https://www.researchgate.net/publication/228683789_Standard_daylight_coefficient_model_for_dynamic_daylighting_simulations by D. Bourgeois , C. F. Reinhart and G. Ward. In Appendix A: DDS sky division and solar position scheme, there is a formula which I presume is what Radiance uses. This gives:

      0 = 145
  1 = 577
  2 = 2305
  3 = 9217

  5. Looking through the code I can see on line 159 az_count, alt_count = 72, 18 which are then multiplied by the sky density value but I am lost after that.

  6. And finally, looking at the skymask mesh using a single point over a plane I get the following number of faces (which I’m not sure means anything but seemed the only way to test the output in grasshopper):

    0 = 1296
    1 = 1296
    2 = 5184
    3 = 11664
    4 = 20736

So, I haven’t found anything definitive and may have missed something. I would also be interested in understanding the 1% error claim seen in the tool tip Shading Mask - Ladybug - Component for Grasshopper | Grasshopper Docs and LB Primer.

Appreciate any advice!