[Radiance-general] Gendaymtx and ground

[Ruggiero Guida]

Hi Andy

I think I got it now. My plane cannot be infinite so I need the first value
in gendaymtx for every ray (pointing towards the lower hemisphere) that
does not intersect the provided ground surface.

Cheers
Ruggiero

On Sat, 2 Jul 2016 at 09:19 Andy McNeil <mcneil.andrew at gmail.com> wrote:

> 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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