Hello Radiance people
1) Anything wrong with this idea?: �If venetian blinds are involved,
to get to the daylight factor with an overcast sky environment,
cut a corner by using a few primitives with complex behaviour to
approximate the gross daylight fluxes through the blinds, instead of
modelling the same using an awful lot of fiddly primitives albeit
with simpler materials.� (More details below.)
2) If you have tried to use BRDFs or other types of materials with
the same idea in mind do you have experiences to relate,
supportive or otherwise?
3) Does anybody know where I can get good data on venetian blinds re
typical performance and typical material surface properties?
I�m usually under pressure to give the right answer yesterday, at all
costs and at no cost. So I went for quick and dirty. I asked around
whether quick and dirty would be fine if in professional hands
with some of the others here.
This generally got a lot of smiling for some reason; personally I can�t
see how being forced into lack of rigour due to expedience could be
cause for amusement in any true professional. I took their smiling as
showing their support for my approach.
The supporting environment was no magnificent computing facilities,
no Unix, no full-scale lab test rigs, no photometers etc., as yet no
Cygwin, Photon Map, or Raydirect/Exergia's radiance
preprocessors for blinds/mktis, or anything more recent than the
compiled binaries from DeskTop Radiance. I haven�t tried using
prismatic materials yet. I�ve also yet to read the 2001 paper on daylight
simulations for a full-scale test office with outer venetian blinds that
Christoph Reinhart kindly sent me, and the stuff re Photon Maps.
Adding onto all that is my general ignorance and minimal Radiance
experience, so you'll agree that it's a truly impressive setup.
Reasonable rigour for my purposes was expectation of a daylight factor
end figure being within 2:1 of �actual�. I.e. the final answer only needed
to distinguish whether the daylight factor was either say 0.5% to 1%,
or 1% to 2%.
The rad files I made grossly simplified the building�s complex facade so
as to more easily do the computing and extract the daylight factor
statistics I needed from the Radiance lux levels.
The daylight problem was a large geometrically complex multi-storey
atrium building, with a triple-glazed fa�ade with 3 kinds of glass and
interstitial venetian blinds, proposed for a built-up city centre location
with complex geometry and lots of materials to model. The design basis
was the usual overcast sky. Not interested in direct sunlight.
Clearly there�d have been some differences from the real world in
assuming the materials and surface reflectances etc., but I'd only
wanted the rough illuminance distributions anyway; not the fine details.
So being neither purist nor pure, I pressed on and:
- modelled a small Test Room A with the triple fa�ade modelled
accurately in geometric detail, using Optics5 data for each sheet
of glass, and assumed reflectances and detailed geometry for the
- modelled a Test Room B of the same dimensions, but with a
pseudo-fa�ade of simple plane elements with BRDFs,
- tweaked the BRDFs until the renderings compared well between
Rooms A and B under 3 outside environments, with external
obstructions, materials and ground planes,
- applied the fa�ade and BRDFs of Test Room B to my big models,
so I can crank out the illuminances and extract the daylight statistics.
Et voil�, yet how far will I be able to trust the end result?
Possibly related stuff found in these threads:
- Gerold Furler - query on BRDF - Venetian blinds
- Feb 1995
- Greg Ward - Amarpreet Sethi - Barbara Matusiak -Peter
Apian-Bennewitz -Carsten Bauer - - �Modeling blinds -
Suggesting photon-map� Oct 2003.
- Greg Ward -Jack de Valpine - Daniel Lash - Alex Summerfield -
- �Query about accurately modelling glazing� Jan 2004.
- Anthony Farrell - Phillip Greenup - Jack de Valpine - -
�Prismatic glazing-blind reflector system analysis�
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