[Radiance-general] Specular Reflections with the Daylight Coefficient Method

[Guglielmetti, Robert]

Greg, all:

So what is the protocol for determining the number of patches the sun's energy is distributed across? In Axel Jacob's (excellent) tutorial on rtcontrib three patches are used to represent the sun regardless of whether the Tregenza or the finer Reinhart patch density/distributions are used, but you mention one to four patches being used, Greg. How or when would this number change? Does genskyvec actually make a choice?

- Rob 
________________________________________
From: radiance-general-bounces at radiance-online.org [radiance-general-bounces at radiance-online.org] On Behalf Of Greg Ward [gregoryjward at gmail.com]
Sent: Tuesday, June 01, 2010 10:33 AM
To: Radiance general discussion
Subject: Re: [Radiance-general] Specular Reflections with the Daylight  Coefficient Method

Hi Kevin,

The daylight coefficient method usually puts the sun's energy into 1
to 4 sky patches, so the rtcontrib method will work, though it won't
give very accurate shadows.  The total energy should still be correct
if you do it right.

Another approach is to create a set of suns at different positions in
the sky corresponding to the expected trajectory throughout the year,
and interpolate these results in a separate rtcontrib run.  I have
done it both ways, and the latter technique tends to produce slightly
more accurate shadows.  The -dr option will work properly if you do
this to calculate reflected beam radiation.

I regret that I don't have a script to provide,  but my 2005
presentation covers this in overview:

        http://www.radiance-online.org/radiance-workshop4/cd/website/PDF/Ward_rtcontrib.pdf

Cheers,
-Greg

> From: Kevin Thuot <kthuot at mit.edu>
> Date: June 1, 2010 6:50:05 AM PDT
>
> Hi,
> I'm trying to use the daylighting coefficient method (using
> rtcontrib) to get annual simulation results for a room equipped with
> a mirrored daylighting system (like a light shelf, for example). Is
> this possible? I know that by using the -dr option, Radiance will
> create virtual light sources to account for specular reflections of
> direct light from the sun. However, since the daylight coefficients
> are calculated using a blank sky having a uniform luminance
> distribution, there is no sun for the -dr option to find. I believe
> this would make the sky patch coefficients come out lower than they
> should be because the specular direct reflection of the sun would
> not be included, but my understanding of how the program works may
> not be correct.
>
> Can the daylight coefficient method be made to work with specular
> reflections in Radiance, or is this not possible given the way the
> program is implemented?
>
> Thanks,
> Kevin Thuot

_______________________________________________
Radiance-general mailing list
Radiance-general at radiance-online.org
http://www.radiance-online.org/mailman/listinfo/radiance-general