"Tor Olav Kristensen" wrote:
> It IS possible to model with NURBS in POV-Ray, by using SDL.




splines, which can be regarded as uniform, non-rational B-splines.



Rune

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"Rune" <aut### [at] runevisioncom> wrote:
> "Tor Olav Kristensen" wrote:
> > It IS possible to model with NURBS in POV-Ray, by using SDL.
>

>

> splines, which can be regarded as uniform, non-rational B-splines.
>

>
> Rune

http://news.povray.org/povray.binaries.images/thread/%3CXns935A4D394502torolavkhotmailcom%40204.213.191.226%3E/?mtop=10


Tom

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"Tom York" <alp### [at] zubenelgenubi34spcom> wrote in message 
news:web.4722362c8d03a40e7d55e4a40@news.povray.org...
> "Rune" <aut### [at] runevisioncom> wrote:
>> "Tor Olav Kristensen" wrote:
>> > It IS possible to model with NURBS in POV-Ray, by using SDL.
>>

>>

>> splines, which can be regarded as uniform, non-rational B-splines.
>>

>
>
http://news.povray.org/povray.binaries.images/thread/%3CXns935A4D394502torolavkhotmailcom%40204.213.191.226%3E/?mtop=10

Ah okay, I misunderstood the "by SDL" part in Tor's message. I thought he 
meant modeling NURBS by SDL, not implementing NURBS by SDL.

Rune

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"Tor Olav Kristensen" <tor### [at] TOBEREMOVEDgmailcom> wrote
> somebody wrote:

> > ...B-rep modelling, whether mesh or
> > NURBS is also a must, neither animation nor manufacture is easy or
natural
> > with implicit "modelling" as in SDL, which only made sense 20 years ago
when
> > realtime b-rep modelling wasn't feasible on a budget.

> It IS possible to model with NURBS in POV-Ray, by using SDL.
>
> BUT it is very hard to model with it without having the
> possibility to move the control points around (or changing
> the weights or the knot vectors) with a pointing device
> like e.g. a mouse.

Well, that's the point. It is of course possible to model *any* mesh or
NURBS based model within the SDL, after all, I am pretty sure that the SDL
is equivalent to a universal Turing machine. You could, if all else fails,
place ten million triangles by hand. That doesn't mean it's desirable or
feasible to do so. Nobody that I know of models NURBS surfaces by typing
down control points, knot vectors, weights and trimming profiles by hand in
a production environment.

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delle wrote:
> Take a look to Indigo Render Gallery:

Color me unimpressed. Maybe it's because I'm not an expert, but some of 
the sub-surface scattering stuff is the only stuff that looks 
particularly good to me. Balanced against most of their proud gallery 
being obnoxiously grainy, I don't see it as a win just from the photos.

Is it possible to automatically know when a scene is good enough? Or 
does it take human intervention to say "ok, stop now and move on to the 
next frame"?

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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> delle wrote:
>> Take a look to Indigo Render Gallery:
>
> Color me unimpressed. Maybe it's because I'm not an expert, but some of 
> the sub-surface scattering stuff is the only stuff that looks particularly 
> good to me. Balanced against most of their proud gallery being obnoxiously 
> grainy, I don't see it as a win just from the photos.
>
> Is it possible to automatically know when a scene is good enough? Or does 
> it take human intervention to say "ok, stop now and move on to the next 
> frame"?

--- Indigo's Gallery ---
There is a lot of beautiful art there, no doubt.  The modeling of the
scenes is particularly good in most cases. I'm not totally convinced
at the quality of Indigo though...

Many images there are grainy, or contain grainy spots.

Many of the global illumination (radiosity) scenes had posted times
over 12 hours, when I'm sure equivalent scenes in POV would
render in less time (usually) and not be grainy.

Only a few of the glassware images even tried to reproduce any
IOR or photons, and looked particularly fake in most cases.

--- NVIDIA's Gelato Gallery ---
There's some pretty amazing scenes here that have a huge amount
of geometry.  If I wanted to trace a billion triangles I'm sure NVIDIA
cards could do it in some manner.

The global illumination here seems to suffer from being grainy,
like Indigo, maybe a little grainier.

Glassware is much better than Indigo's, good photons,
somewhat blocky edges at times.

The subsurface scattering looks nice (we should put this into POV).

Many of the images seemed saturated.

--- Maxwell's Gallery ---
Just stunning, very good in most every respect.

I did notice just a couple grainy spots, but you needed to look for
that, mostly it's not obvious.

Of course setting this package up with their modeler will set
you back about 3400 pounds... $7000

--- Maya / Mental Ray / AutoCad ---
Yes, Autodesk is now selling Maya with Mental Ray licenses.
Equivalent or better than POV in quality, with a proven
track record.

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4722f06c@news.povray.org...
> Many of the global illumination (radiosity) scenes had posted times
> over 12 hours, when I'm sure equivalent scenes in POV would
> render in less time (usually) and not be grainy.

The problem being that doing equivalent scenes in POV-Ray (particularly 
interior scenes) is, from a practical point of view, impossible. Light 
sources in POV-Ray are much too primitive for that, there's no support for 
true area lights or good-looking blurred reflections and while there are 
situations where it's more or less possible to simulate this (using various 
tricks), in most cases it just doesn't work. Jaime is probably the POV-Ray 
artist who has done the most research in that, and his best results, 
impressive as they are from a POV-Ray perspective, are just not in same 
league and are plagued with radiosity artifacts and area light graininess.
http://www.ignorancia.org/en/index.php?page=Modern_interior

Even with the grain, the quality of the illumination in unbiaised renderers 
is unparalleled, simply because there's no cheating involved.

G.

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What unbiased methods give you is certainty. If you leave them long enough
they *will* approach the true solution. The rendering times usually needed
to reduce grain (without post-processing, anyway) are impressively long,
but if you add tweaking and re-rendering time to shift stubborn artefacts
from radiosity, I'm not so sure the comparison is much in POV's favour.

On the other hand, while path tracing et al are nice and all, I'm pretty
sure these methods could *not* be added to POV as it currently is without
massive internal changes. They require sophisticated sampling support for
all render steps to be practical at all. Is the effort worth it?

This thread and others have pointed out that there are actually plenty of
free renderers out there that make unbiased methods their specialty. Why
one more? Programs like PBRT were designed from the ground up to support
multiple approaches to solving the rendering equation, and it shows in the
code. POV wasn't, in fact it's tedious enough to make even minor
alterations to the way it currently works.

Instead I think there is something to be said for sticking to a ray tracer +
global illumination approach. Replacing the existing radiosity method with
something based on photon mapping would help tackle the artefacted GI
problem, but that would be the most major change needed that I can think
of. As a raytracer POV may not be exceptionally fast, but the
(non-commercial) competition I've tried out seem surprisingly slow, and
people still use them. I think there is still demand for fast raytracing
with some occasional GI, why not focus on that?

Tom

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Gilles Tran wrote:

> The problem being that doing equivalent scenes in POV-Ray (particularly 
> interior scenes) is, from a practical point of view, impossible. Light 
> sources in POV-Ray are much too primitive for that, there's no support for 
> true area lights or good-looking blurred reflections and while there are 
> situations where it's more or less possible to simulate this (using various 
> tricks), in most cases it just doesn't work.

Wait... since when does POV not have "true" area lights?

> Jaime is probably the POV-Ray 
> artist who has done the most research in that, and his best results, 
> impressive as they are from a POV-Ray perspective, are just not in same 
> league and are plagued with radiosity artifacts and area light graininess.
> http://www.ignorancia.org/en/index.php?page=Modern_interior
> 
> Even with the grain, the quality of the illumination in unbiaised renderers 
> is unparalleled, simply because there's no cheating involved.

Perhaps everybody else is looking at different pictures to me...? I 
think these ones look *better* than the ones from Indigo. (Sharper, more 
crisp, and more detailed. The colours seem more vivid too. I don't know 
whether this is an effect of the renderer or just better scene design...)

Seriously. I'm failing to see anything POV-Ray can't already do. 
(Especially if you leave it to render for *this* long!) Also, I was 
somewhat amused to see quite a few images that appear to be using 
polygons rather than real curves... No cheating? I think not.

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Tom York wrote:
> What unbiased methods give you is certainty. If you leave them long enough
> they *will* approach the true solution.

So will POV-Ray's radiosity system, if you turn the settings up high 
enough. (And wait a damn long time...) Your point?

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