[Radiance-general] how to split vertical illuminance level into light coming from sky and light reflected by surface?

[Thomas Bleicher]

Ji.

Interesting concept.

On Mon, Jul 26, 2010 at 4:20 AM, Ji Zhang <hope.zh at gmail.com> wrote:
> Dear Radiance experts,
>
> We're trying to explore the relationship between Vertical Daylight Factor
> and Facade Sky View Factor.

In the UK we have the "Vertical Sky Component" which quantifies the
_direct_ contribution of the sky to a point on a vertical plane (ie.
wall). Because it's only the direct component that matters here it is
related to the portion of sky visible from this point. It's also based
on the CIE overcast sky so it matters which part of the sky you can
see. Is that the same concept as your "Facade Sky View Factor"?

> By Vertical Daylight Factor we mean the ratio of the illuminance level of a
> point on vertical building facade (i.e. the vector of the sensor of that
> point is perpendicular to the facade surface) to the illuminance level of a
> point on horizontal plane under standard CIE overcast sky (please correct me
> if the definition is wrong).

Does that include the reflected part?

> Via Radiance, is there a way to split the illuminance level of a point on
> vertical surface into 1) the light coming directly from the sky dome and 2)
> the light reflected by surrounding building surfaces and ground plane?

For the direct part simply use "-I -ab 1" in your rtrace command (or
"-i -ab 1" if you want to calculate pictures):

echo "0 0 2 0 1 0" | rtrace -w -h -ab 1 -I scene.oct | rcalc -e
'$1=($1*0.265+$2*0.67+$3*0.065)*179' > facade_direct.lux

Then calculate the total of direct and reflected component by
increasing "-ab" to an appropriate value:

echo "0 0 2 0 1 0" | rtrace -w -h -ab 4 -I scene.oct | rcalc -e
'$1=($1*0.265+$2*0.67+$3*0.065)*179' > facade_total.lux

The reflected light is the difference between total and and direct
component. You can also render images and subtract the images from
each other. See the 'pcomb' command for details.


Regards,
Thomas