[Radiance-general] Re:Materials for scale model room
Federico Giovannetti
f.giovannetti at isfh.de
Tue Sep 13 11:23:48 CEST 2005
Thanks John, Francesco and Peter for your answer.
Regards,
federico
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> 1. Re: Materials for scale model room (Peter Apian-Bennewitz)
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> Date: Sun, 11 Sep 2005 00:10:47 +0200
> From: Peter Apian-Bennewitz <apian at pab-opto.de>
> Subject: [Radiance-general] Re: Materials for scale model room
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> radiance-general-request at radiance-online.org wrote:
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> >Today's Topics:
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> > 1. Materials for scale model room (Federico Giovannetti)
> > 2. RE: Materials for scale model room (Francesco Anselmo)
> > 3. Materials for scale model room (John Mardaljevic)
> > 4. Re: Obtaining RGB output data (alira at gsd.harvard.edu)
> > 5. Re: Obtaining RGB output data (Greg Ward)
> >
> >
> >----------------------------------------------------------------------
> >
> >Message: 1
> >Date: Thu, 8 Sep 2005 12:38:40 +0200
> >From: "Federico Giovannetti" <f.giovannetti at isfh.de>
> >Subject: [Radiance-general] Materials for scale model room
> >To: <radiance-general at radiance-online.org>
> >Message-ID: <002901c5b461$7a5cb2d0$e400a8c0 at PC501fg>
> >Content-Type: text/plain; charset="iso-8859-1"
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> >Hallo Greg, hallo Radiance Community!
> >
> >I'm trying to compare some Radiance-simulation results with experimental
measurements (i know it's not that easy, i'm just trying).
> >As I would like to isolate (as good as possible) the effects of glazing
system and skylight distribution, i'm looking for diffusing materials for my
scale-room which can be physically very good modeled with Radiance. That
is materials whose BRTDF is not more complex than a TRANS-type. So that i
don't have to worry too much about them (??).
> >Some textil materials (such as molleton for theater applications) seem
to be good diffusing ones, with an almost lambertian behaviour, but i'm
still searching...
> >Has anybody in the community a good tip (matt paint, etc.)?
> >
> >
> Hi Federico,
>
> my two cents thoughts on validations in general: Rather simple ideas
> really. Sorry if they are a boring repetition of standard engineering
> procedures to many of you. Having watched and read some Phds on this
> subject, it seems worth mentioning so. Many other works on the subject
> don't need any of my humble comments. Nothing personal: "you" is just
> to-whome-it-may-concern.
>
> * Your results will most likely /not/ match you simulation. Be
> prepared to figure out why. Don't just say "oh, they are 15% off
> at point A und only 5% at point B, so we're better than 15%.
> Homework done, can I go play outside ?" . Check what's happening
> between point A und B.
> Compare whole curves rather than individual points to see whether
> there's an offset or a complete different shape. Both cases ask
> for an explanation.
> If they match perfectly, vary some parameter and check that the
> match results from you doing the right thing and not from sheer
luck.
> If simulation and measurement differ by Monte Carlo and/or
> measurement noise, you're knighted and may retire to a splendid
> location on the planet.
> The aim of a validation is not so much an impressively small
> deviation between simulation and measurement, but a proven
> understanding of the mechanisms that lead to the deviations.
> * nature lies to you cold blooded at any moment you're not alert.
> Start with the simplest imaginable case and check that. Build
> trust in your results by adding complexity stepwise and in a
> controlled manner.
> * Keep track of your setup, materials and procedures. If you find
> out at a late stage that rho_dh of molton differs mysteriously
> from the value measured at the beginning (maybe because the large
> piece of molton that was cut down to smaller patches wasn't
> homogenous), you want to know which measurements might have been
> affected by this. Be prepared to recheck. That of course works
> more easily with automated measurements than with long runs of
> pure hand measurements.
> Unless you're taking data on Nessie or Mt. St. Helen, plan to
> repeat a measurement. Just for the fun of it and to see whether
> nature is still on your side.
> * get as much data points as you can. Timewise (some people are
> suprised to find that artifical lamps have a 50/60Hz modulation
> and that shows if values are not averaged over a longer period or
> if no special power source is used. output decrease with age, too)
> and spatial. IMHO the latter is higher valuable:
> Measurements at 3 points in a box are, at least to me, not enough
> to understand what's happening inside.
> * really diffuse reflecting materials are hard to find and it gets
> harder with higher incident angle (away from the surface normal)
> * "The systematic experiment", edited by J.C. Gibbings, Cambridge
> Univ. Press 1986 has some introduction to this art. Likely there
> are a piles of similar nice texts available.
> * Don't trust your superiors telling you that this bit of extra
> effort is not worth it.
> * To the superiors: Allocate enough money to do it right.
> Validations are like antibiotics: Do it fully or don't do it at all.
>
> anyway, - enough nagging comments,
> cheers
> Peter
>
> --
> pab-opto, Freiburg, Germany, http://www.pab-opto.de
> [see web page to check digital email signature]
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