Confusing output vertical venetian blinds - BSDF xml-file error?



I created four BSDF xml files for vertical venetian blinds and four states: 0, 45, 90 and 135 degrees (-45).
Simulation gave me strange results. because the state with 45 degrees don’t seem to do much.
Could someone look to my BSDF-files? I probably made a mistake because the illuminance values for the 45-degrees state are relative high, but I can’t find the mistake.

I attached a simplified script below together with the bsdf-files.

BSDFs_15_5_2019_Kim.rar (646.2 KB) (427.0 KB)

Thank you so much in advance!

Kind regards,

Kim Bodde


I ran a 3-Phase image-based simulation for a south-facing room on your xml files.

You can download the above images here:
Filenames beginning with After correspond to a clear sky in New York City on 20th January at 3:30 PM. Those beginning with Mor correspond to a clear sky in NYC on 20th January at 8:30AM. Finally, those beginning with Noo correspond to a clear sky at Equator (latitude of 0.78 degrees but same longitude as NYC) on 20th June at 12PM. So, the results with After and Mor relate to low angle radiation causing direct insolation into the room while Noo relates to high angle radiation that will hit the slats of the blinds almost completely vertically. Following the prefixes of After, Mor or Noo, the remaining filename corresponds to the name of your BSDFs. So, MorDouble_glazing_low_emission.tiff is the result for NYC on 20th January at 8:30AM with Double_glazing_low_emission.xml. Assuming all of this is clear, your results seem okayish to me. The open blinds, closed blinds and glazing-only scenarios are simple and appear to be in order.

The +45 and -45 blinds appear to block of high altitude sun in the same manner. This seems reasonable.
The +45 blinds let in low-angle radiation from the east (in the morning) while the -45 blinds block them off.
The behavior is flipped in the afternoon for radiation from the West.
To address your query, the 45 degree blinds are obviously doing something although I don’t know if this is the intended behavior. Do you expect the position of vertical slats to have different impact on shading based on azimuth angle? Creating BSDFs with genBSDF will give you greater control on how they behave, however, it does involve a whole lot of prep-work. You can refer Andy McNeils tutorial for that:
If you can get it to work (given how long it has been since it was last updated), you can analyze your bsdfs with Andy"s BSDF viewer:


(PS: It’s way too much work for me to run Grasshopper on my computer at the moment. Perhaps @mostapha can help with troubleshooting that file if required.)