Hey all - quick question: do we need to model a ground plane when using DIVA in grasshopper?  Previous posts on this forum have said yes, but I noticed that there is a hidden input in the annual component that says 'ground reflectance."  If I modify this, it changes the daylighting results. That would lead me to believe that it is adding a ground plane automatically?  

Tags: ground, plane

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Every simulation includes a glow source for the ground, which emits whatever luminance a horizontal lambertian diffuser would under the given sky condition.  This glow source doesn't accept shadows or reflected light in the scene, however, so it is likely inaccurate in the vicinity of the model, where the presence of your building (and other context) would affect ground brightness.

So it sounds like the answer is yes, but it is an idealized case that will overpredict simulation values to some degree.  What prompted this question for me is that I notice when I had a modeled ground plane, it increased the daylight values by like 2-3x, especially when using simulation settings with 3 ambient bounces.  It seemed like it was way too high of an effect.  Has anyone else ran into this?

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