[Radiance-general] Sunlight through glass
Rob Guglielmetti
rpg at rumblestrip.org
Wed Jan 18 19:09:07 CET 2006
Jack de Valpine wrote:
> Hi Giullio and others following this thread,
>
> <RANT MODE>
> It seems to me that this is a problem with proprietary shrink wrap
> software renderers. Who really knows what is going on under the hood,
> whose word should be taken for the validity of the physical model,
> what validations have occurred?!
>
> Users see the product marketing materials that talk about Global
> Illumination and "physical accuracy," and they believe the hype! That
> seems to me to be pretty dangerous if you are going to be using the
> tool to somehow "validate" design issues!
Can I get an amen-ahh!
I got into it with a CAD/modeling pundit several years ago, when he
stated in a review that Viz was capable of producing renderings that
were "95% accurate". What the hell does that mean? Well, I asked him,
and he said he spent a full day with Stu Feldman (one of the two
founders of Lightscape), and that was what he walked away with. I told
him he didn't get his money's worth on the half-day seminar. We went
back and forth on this, I told him he was doing his readers a great
disservice, and in the end I was made to feel like a loser for being in
such a small industry that no one cares about. Something about "if you
want to stick with Lightscape, good luck, it's not going to be supported
anymore, blah blah..." The good news is, it forced me to finally learn
Radiance. =) The problem is that that review went into Cadalyst
magazine, which is read by lots of Architectural CAD drafters and
renderers, and as you mention they aren't necessarily concerned with the
goings on under the hood. And then you have people showing renderings
to clients and saying "oh yes, that's what it will look like, we used
software that's 95% accurate!" Which is amazing, since many of these
people driving the program don't know how to read a polar curve on a
luminaire cutsheet. Oops.
>
> I know that there are systems that have implemented GI to varying
> degrees and sophistication. But the problem is you probably have to be
> an uber expert to use them and/or code up custom material/lighting
> shaders. Still though the question is what validation has occurred. I
> think that most commercial renderers and users of said systems are
> really not that interested in physical validity, they are most
> interested in the outcome/appearance of the final image. It does not
> really matter how it get there.
...and if the result looks nice in half the time, screw accuracy. That
was a lot of the complaining I saw on the M-R forums, was how slow it
was. It's comments like that that really give you insight into how
little these people understand the problem of solving GI.
>
> It seems to me that the one commercial product that showed some hope
> in its original (pre-acquisition) form was Lightscape. However, Rob
> Guglielmetti has explored and written pretty extensively on this topic
> seemingly with only partial satisfaction (my apologies to Rob G. for
> such a cursory summary, he did some really excellent work on this).
> Note I also believe that the original developers of Lightscape were
> truly interested in enabling people to use a tool with a reasonable
> and practical level of physical validity.
> </RANT MODE>
Thanks Jack. I was merely trying understand the product's limitations
because I wasn't ready to commit to learning radiance in production.
=8-) And you are right about the developers. At least in the case of
Rod Recker (the other Lightscape developer), I definitely felt like he
was interested in giving the world a tool. Sure, getting rich off it is
a nice bonus, but he seemed to be interested in taking that Cornell
education and channeling it into a lighting tool. He's a really nice
guy and wish him the best of luck at Autodesk. It's truly unfortunate
what happened to that product, but then again it was severely limited in
what it could do. Of course, who knows what it'd be like today had the
right people stayed in the decision-making seat. Then again, how far
can one go with radiosity? (Well, I guess the folks at Lighting
Analysts can answer that one, and the answer is "pretty damned far".
Their AGI product continues to improve, and with people like Martin at
PSU doing validations with it, it becomes more and more robust. But I
still prefer Radiance.)
Interesting thread; sorry for the somewhat off-topic verbiage, but I
think we all learn from these exchanges too.
- Rob Guglielmetti
www.rumblestrip.org
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