Gendaymtx and ground

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

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):

Best,
Andy

···

On Fri, Jul 1, 2016 at 9:52 PM, Ruggiero Guida <[email protected]> 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

_______________________________________________
[email protected]

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 <[email protected]> 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):

Best,
Andy

On Fri, Jul 1, 2016 at 9:52 PM, Ruggiero Guida <[email protected]> > 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

_______________________________________________