[Radiance-general] Gendaymtx and ground

[Andy McNeil]

Hi Ruggiero,

If you have ground surfaces in your model (which you should - it's good
practice) you should still use the first value in gendaymtx. The
contribution from your ground surface will be included as reflected light
from sky patches. But, the gap between your ground surface and the horizon
is filled in with the ground patch luminance from gendaymtx. This is
illustrated by figure 7 & 8 in the three phase tutorial (though the advice
is also relevant for daylight coefficient simulations):
http://radiance-online.org/learning/tutorials/Tutorial-ThreePhaseMethod.pdf

Best,
Andy


On Fri, Jul 1, 2016 at 9:52 PM, Ruggiero Guida <ruggiero.guida at gmail.com>
wrote:

> Hi,
>
> I am trying to understand how to use the results from gendaymtx when my
> ground is not flat but it is represented by a generic surface.
>
> The first patch generated by gendaymyx is for the ground and it has the
> units of W/sr/m2. It has a constant value for each direction below the
> horizon.
>
> If I consider a surface dA placed 1 m above the ground (assumed flat for
> now) and pointing downwards, I would measure:
>
> g x 2 x Pi [W/m2]
>
> This is assuming that I have used the typical descriptions for the ground
> geometry as an hemisphere below the horizon and that there are no
> obstructions as these would change the light that is reflected from the
> ground.
>
> Is this correct?
>
> If it is, then in order to consider grounds with generic surfaces I should
> ignore the first value in gendaymtx and use the actual geometry for the
> ground.
>
> Does this make sense?
>
> Thanks
>
>
>
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