nemesis schrieb:

> Lighting is not quite the same but worse:  he seems to have gone for 
> surrealism as the liquid inside seems to go beyond the glass sides, like 
> as if molten with it...

That's actually realistic.

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scott schrieb:

> That's what I don't understand, Fresnel should determine the reflection 
> % based on the IOR and the angle, nothing else, I don't get what the 
> other two parameters do in this cae, or what I should set them to.  I 
> just use reflection{1 fresnel on} for now - I hope that is physically 
> correct.

To get physically correct results (well, as close as you get with 
POV-Ray's "fresnel" feature), it should be:

     reflection { 0, 1 fresnel on }

though for convenience the syntax

     reflection { MAX fresnel on }

is interpreted as:

     reflection { 0, MAX fresnel on }

so the syntax you use does work as well.

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clipka schrieb:
> scott schrieb:
> 
>> That's what I don't understand, Fresnel should determine the 
>> reflection % based on the IOR and the angle, nothing else, I don't get 
>> what the other two parameters do in this cae, or what I should set 
>> them to.  I just use reflection{1 fresnel on} for now - I hope that is 
>> physically correct.
> 
> To get physically correct results (well, as close as you get with 
> POV-Ray's "fresnel" feature), it should be:
> 
>     reflection { 0, 1 fresnel on }
> 
> though for convenience the syntax
> 
>     reflection { MAX fresnel on }
> 
> is interpreted as:
> 
>     reflection { 0, MAX fresnel on }
> 
> so the syntax you use does work as well.

I have closely examined the code by now, to find out the following:

- The code does indeed implement the exact Fresnel equations for the 
special case that the incident light is unpolarized, though I have not 
the slightest clue how; the implemented function doesn't look anywhere 
close to anything I've been able to find on the 'net so far. But the 
values are flawless.

- when specifying "reflection{MIN,MAX fresnel on}", this will reduce the 
maximum reflectivity to MAX, while at the same time increasing the 
minimum reflectivity. However, MIN in this case is /not/ to be taken 
literally as the minimum effective reflectivity; instead, it specifies a 
kind of "zero reference" for reflectivity calculations; i.e. if the 
minimum reflectivity according to the Fresnel equations would be 
FRESNEL_MIN, the resulting effective minimum would be MIN + 
FRESNEL_MIN*(MAX-MIN).

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>> To get physically correct results (well, as close as you get with 
>> POV-Ray's "fresnel" feature), it should be:
>>
>>     reflection { 0, 1 fresnel on }

...

> - when specifying "reflection{MIN,MAX fresnel on}", this will reduce the 
> maximum reflectivity to MAX, while at the same time increasing the minimum 
> reflectivity. However, MIN in this case is /not/ to be taken literally as 
> the minimum effective reflectivity; instead, it specifies a kind of "zero 
> reference" for reflectivity calculations; i.e. if the minimum reflectivity 
> according to the Fresnel equations would be FRESNEL_MIN, the resulting 
> effective minimum would be MIN + FRESNEL_MIN*(MAX-MIN).

Thanks for the confirmation, it was something that was not really very clear 
at all in the docs.

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>> For me the hardest part is getting the lighting correct now, either the 
>> torii are too bright or the floor is too dark in the reflections.  Using 
>> Fresnel should give 100% reflection around the edges of the torii, so I 
>> don't know why the floor is coming out so dark.
>
> Looks to me like you're not getting the right illumination on your floor, 
> and that light intensity falls off drastically towards the horizon...?

Yeh, I'm struggling to replicate the lighting, I'm not sure how they manage 
to get the main scene lit by that box-light (that you can see in the 
reflection, and causing the caustics) but keep the plane well lit all the 
way out.  I could hack together something to boost the lighting out there, 
but it doesn't seem right.

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clipka wrote:
> nemesis schrieb:
> 
>> Lighting is not quite the same but worse:  he seems to have gone for 
>> surrealism as the liquid inside seems to go beyond the glass sides, 
>> like as if molten with it...
> 
> That's actually realistic.

thinking about it... it turns out perhaps the glass walls came out too 
thick.  That's the problem of taking a reference picture of glass with 
all the refractions set and trying to draw the actual walls from it. 
They're going to be slightly off, sure.  I'll rework it and try a new 
render...

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> Looks to me like you're not getting the right illumination on your floor, 
> and that light intensity falls off drastically towards the horizon...?

OK I fixed it.  The dark areas in the reflection are actually the sky, not 
the floor!  So I put a white sky in there (instead of black) and it looks 
exactly right now. (the dark area in the reflection *is* the floor in the 
distance)

Going away for a business trip for a few days so won't be able to post the 
result until later next week - but should give MCPOV a good time to smooth 
out the noise :-)

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scott schrieb:

> Thanks for the confirmation, it was something that was not really very 
> clear at all in the docs.

I'd even go as far as to say it isn't in the docs at all :-)

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clipka wrote:
> scott schrieb:
> 
>> Thanks for the confirmation, it was something that was not really very 
>> clear at all in the docs.
> 
> I'd even go as far as to say it isn't in the docs at all :-)

Time to warn Jim Holsenback (is the spelling right?).  Isn't he 
documenting the latest pov?

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nemesis schrieb:
> clipka wrote:
>> scott schrieb:
>>
>>> Thanks for the confirmation, it was something that was not really 
>>> very clear at all in the docs.
>>
>> I'd even go as far as to say it isn't in the docs at all :-)
> 
> Time to warn Jim Holsenback (is the spelling right?).  Isn't he 
> documenting the latest pov?

Well, he's /head/ of the documentation project. I hope he doesn't have 
to do it all on his own...

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