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Post by George Tirebiter on Apr 26, 2009 17:30:44 GMT -4
Backscatter can be modeled on top of that with a generalized Torrance-Sparrow model.I was thinking in terms of the models that are commonly "built-in" to most rendering software. Usually that's Cook-Torrance instead of Torrance-Sparrow, but because of Cook and Torrance's crude geometric shadowing function (understandable when first published, but why are people still using it?) it looks terrible when used for rough surfaces. But we haven't gotten there yet.We haven't? Drat.
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Post by ampingu on Apr 27, 2009 4:48:43 GMT -4
It sounds, from what you say, that CG people are misusing the term, which seems a bit silly if they are. You may have a point. Im not really a cg person - certainly not in the context of scientific models. I tend to use the software only as an artistic medium. If I dare defend my apparently slightly lacking understanding of some of these intricacies (Im learning a lot here).... Id say a full understanding isnt necessarily important, since cg models are often more about artistic interpretation and a pretty end result. Youll probably agree that precise, physically correct models arent always conducive to a scene that looks right to the eye. Nice forum, btw. Lots of smart people. Its refreshing. Ps: "Are you saying that this doesnt apply to an overall model?"Depending on the parameters, the result may be illumination which exhibits preferential reflection along the classic specular departure angle, but that is a property of the combined model, not of the specular component alone. I probably missed the point with so many half quoted hazy questions, and I may have taken some of your explanations out of context. Just so Im clear on the terminology for next time, can the term specularity apply as a measure of the extent to which this occurs? Thanks.
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Post by JayUtah on Apr 27, 2009 11:43:26 GMT -4
(One of my lengthy posts seems to be missing from this thread. I have the sneaking suspicion I only hit Preview and not Post.) Im not really a cg person - certainly not in the context of scientific models. I tend to use the software only as an artistic medium.I am a graphics person (since before they started calling it CG or CGI), and I find the techniques useful in many different ways. As an artistic medium: certainly. But even in hard-core engineering -- arguably a highly left-brained pursuit -- accurate rendering is important. I can give you cite after cite from my thesis showing the importance of realistic rendering in the design process. And for 20 years I have lived those principles. The brain works best when given images that look real. Youll probably agree that precise, physically correct models arent always conducive to a scene that looks right to the eye.Yes and no. If you want either a photorealistic scene or an artistically rendered scene, you need to know a lot about the physics of light's interaction with other materials. You need to know why things look like they do. That said, computing it that way is expensive. Torrance and his colleagues, for example, correctly reasoned that the appearance of a surface at the practical level was the result of complex surface geometry at the microscopic level. However, instead of micromodeling the surface (i.e., actually adding that microscopic level of detail to the shape, which would have required considerable storage and CPU power to illuminate), they figured out some short-cut math to approximate the effect. The simplest shading models include an "ambient" term which simply treats as a constant the illumination that derives from complex diffuse interreflection among surfaces in the scene. Conversely people like Michael Cohen, whose office was just down the hall from mine, spends his entire career computing the diffuse interreflection by means of radiosity methods. So yes: it is unnecessary and undesirable to compute through all the physical laws that govern illumination. But it is important to know them, and to study them if only to learn how best to approximate them. Nice forum, btw. Lots of smart people. Its refreshing.*blush* You're asking good questions. Just so Im clear on the terminology for next time, can the term specularity apply as a measure of the extent to which this occurs?Yes. "Specularity" is a very good word for that. I was dogmatic earlier only because you were talking about the specific geometry; that's when you need to be picky. Statements such as "Metals are generally specular surfaces," will work, even among graphics geeks. But if you say, "In AS11-40-5903, the hot-spot behind Aldrin is a specular highlight," objections will be raised because it's not the property of specularity that's causing it.
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Post by fiveonit on Apr 27, 2009 20:21:45 GMT -4
If anyone here would like to dabble in the world of 3D just to try it out. I suggest try using Blender. www.blender.org/If you would then like to render physically accurate scenes using MLT (and don't have enough cash for Maxwell) I would suggest Indigo. www.indigorenderer.com/Yes I've thought of using it many times to "debunk" silly hoax theories. I just wish I was a much better modeler!
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raven
Jupiter
That ain't Earth, kiddies.
Posts: 509
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Post by raven on Apr 28, 2009 14:26:06 GMT -4
I play around in anim8or some, it's great for a newbie, though it is best suited for cartoonish graphics.
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Post by nomuse on May 14, 2009 19:59:21 GMT -4
I just realized, while looking through this thread, the major reason the "spotlight" argument has never seemed in the least bit plausible to me. Okay, sure, I could get something roughly that soft-edged with a sheet of diffusion in my favorite ERS fixture -- or, better yet, with a fresnel fixture. But the hotspot would be LENTICULAR. There's a big mis-match between how the lunar picture presents as a "spotlight" directly over the astronaut's head, and as the evident strong single-source light casting the long shadows off the astronaut's feet. For someone who practices stage lighting almost daily, its a mismatch almost great enough to create a condition of cognitive dissonance in trying to imagine the scene is being lit with the so-called "spotlight."
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