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Joshua Weber avatar image
Joshua Weber asked

MAXtoA Physical Sky producing very bad GI results compared to HDRI

3dsmax native physical sky

maxphysicalsky.jpg

HDRI

hdri.jpgaiPhysical Sky
aiphysicalsky.jpgHello, Im rendering a building exterior with an arnold physical sky and the problem im having is that the interior spaces behind the glass are incredibly dark. This building has a lot of glass on its facades, basically curtain walls so the spaces should be much better lit. Upon using an HDRI instead of a arnold physical sky i noticed the spaces are much better illuminated the difference is night and day however by using an hdri i lose a lot of control so i would prefer to use the physical sky. I have tried adding light portals and cranking the intensity but these do not help. I also used the default 3dsmax physical sky with a sun positioner but was getting almost the same results as the arnold physical sky but just a little more illuminance. I also tested my ray depth settings at 6 with no improvements.


MAXtoA 4.3.2.46

lighting
aiphysicalsky.jpg (223.2 KiB)
hdri.jpg (646.4 KiB)
maxphysicalsky.jpg (640.9 KiB)
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Lee Griggs avatar image
Lee Griggs answered

What happens when you enable caustics for the glass shader?

https://youtu.be/GkVIEV_0Ujs?t=218

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Joshua Weber avatar image
Joshua Weber answered

@

So to enable caustics i switched to using an aiStandardSurface when i was using a physical material before which should be the same but i found that they actually produced very different results when using the arnold physical sky. I ran 3 evnironment setups, one with the physical material, one with aiStandardSurface w/o caustics and one with caustics. I then tested these 3 setups with the arnold physical sky, an HDRI and the 3dsmax physical sky. For all of tests the 3dsmax physical material produced the worse results with the aiStandardSurface with caustics giving the best results. What was interesting was when using an HDRI setup the 3dsmax physical material produced the exact same results as the aiStandardSurface w/ caustics which was not at all the case when using the physical skys where the physical material was much darker. So it turns out it seems to be the shaders that are causing the illumination difference not the environment so from now on ill use the aiStandardSurface as it produced consistent illumination throughout all environment types, sucks its not viewport supported though.

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