[Radiance-general] Daylight factor

[Victor Li]

Actually i just export the model from ECOTECT to RADIANCE, and i chang some
parameters and run the simulation manually like Marija has shown above.

The first time i calculated the daylgith factor in a grid
I run it by define: gensky 12 21 12.00 -c -a 31.400 -o -121.400 -m -120.000
-B 0.558659,
-B 0.558659 means the diffuse horizontal illuminance is 100lux outside then
the internal illuminance is the dylight factor.

The second time i just calculated the internal illuminance in a grid under
overcast sky in the same time as the first time. I defined the sky : gensky
12 21 12.00 -c -a 31.400 -o -121.400 -m -120.000

In the grid, i can calculate the external diffuse horizontal illuminance at
that time under overcast sky in the same point by  the external diffuse
horizontal illuminance = the internal illuminance/ daylight factor.
However, i calculated the the external diffuse horizontal illuminance by
different points the results are different. Actually the results should be
the same because it the external diffuse horizontal illuminance. So why is
it different?




2009/12/13 Thomas Bleicher <tbleicher at googlemail.com>

> Victor.
>
> There are a couple of things you should change. If you can't change the
> options ECOTECT uses you can run the simulation manually as Marija
> has shown above and then read the results back into ECOTECT.
>
> More details within:
>
> On Sun, Dec 13, 2009 at 4:28 AM, Victor Li <victorpermanent at gmail.com>
> wrote:
> > Thank you very much!
> >
> > Actually i uesed ECOTET exported to DESKTOP RADIANCE to calculate.
> > The only differernce between Daylight factor and Illuminance calculation
> is
> > the -B 0.558659 definition in 11_SKY.RAD
> >
> > In Daylight factor calculation the sky is defined as following:
> >
> > !gensky 12 21 12.00 -c -a 31.400 -o -121.400 -m -120.000 -B 0.558659 |
> xform
> > -rz -27.000
>
> I can't see a difference between the two gensky commands below but the
> "-B 0.558659" will create a sky with 100 Lux diffuse vertical illuminance.
> This
> is very low if you want to calculate Lux values. The only reason to do this
> is that you don't have to convert from a 10000 Lux baseline to 100 Lux (or
> %)
> if you want to calculate daylight factors.
>
> Since both setups and scene files (skies) are the same you would
> expect the same values for both calculations. However, your settings
> for the rtrace command are not very accurate so the absolute results
> are going to be different. You haven't told us yet how big the difference
> is, btw.
>
> [copied from an older mail]:
> >> The rtrace setting is "rtrace -I -h -dp 2048 -ar 32 -ms 0.063 -ds .2 -dt
> >> .05 -dc .75 -dr 3 -sj 1 -st .01 -ab 8 -aa .1 -ad 512 -as 256 -av 0.01
> 0.01
> >> 0.01 -lr 12 -lw .0005  -af 11.amb 11.oct < 11.pts > 11.dat"  And the two
>
> For more accuracy I would use something like:
> "-ar 128 -ab 6 -aa 0.01 -ad 2048 -as 256"
>
> Mind you, I don't know anything about your scene so these may not
> be the right settings at all.
>
> The remaining settings are less important in a daylight calculation
> without sun. I would also remove the "-av 0.01 0.01 0.01" because
> that would introduce a large amount of artificial ambient light that
> is too high for you 100Lux outdoor illuminance.
>
> [...]
>
> > skyfunc glow ground_glow
> > 0
> > 0
> > 4
> >      1 .8 .5 0
> >
> > ground_glow source ground
> > 0
> > 0
> > 4
> >      0 0 -1 180
>
> This creates a "ground" hemisphere that is nearly as bright as
> the sky (about 80%). You should reduce the values in the
> ground_glow definition to a quarter of their current setting
> (unless you have ground covered in snow):
>
> skyfunc glow ground_glow
> 0
> 0
> 4
>      0.25 0.2 0.125 0
>
> [...]
>
>
> > In Illuminance calculation, the definition is :
> >
> > !gensky 12 21 12.00 -c -a 31.400 -o -121.400 -m -120.000 -B 0.558659 |
> xform
> > -rz -27.000
> >
> > The rest is all the same.
> >
> > For converting the output, the ECOTECT can convert it automatically.
>
> ECOTECT can read "single" value and "[r,g,b]" value output, but the
> values have to be in the right scale. If you want your DF values
> to mean anything you have to know the outside illuminance of the
> sky and scale all the values if it is anything else than 100 lux.
>
> Hth,
> Thomas
>
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