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I might ramble here, but anyway...
Just thinking about variable IOR today, and I reread the section of the
VFAQ on it. Basically, by specifying variable IOR as a property of
media, the density of the media could be used to vary the IOR. By
supersampling the media enough, it should be possible to get decently
accurate images (even though they may take days or weeks to render {but,
this has never stopped POVers before, has it?}). It should be even
possible to get a more or less accurate derivative of the density
function, and guess the correct length for the next ray segment.
Anyway, however slow it is (again - has slowness ever stopped POVers
before?), does anyone else think it might be time to try it out? Used
properly, this would allow some great effects. Mostly, I'm thinking of
subtle heat shimmers in landscape scenes - but I'm sure there are others.
...Chambers
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Chambers wrote:
> I might ramble here, but anyway...
>
> Just thinking about variable IOR today, and I reread the section of the
> VFAQ on it.
To be frank - if you have read the VFAQ and still think variable IOR
would make sense in raytracing you probably either have not read it
thoroughly or did not fully understand it.
The explanation mentions media to illustrate the approach necessary to
try simulating variable IOR but makes it very clear and explains why the
results would be completely dissatisfying. While scattering media has
an inherent smoothing effect - small features as well as errors in the
simulation are smoothed out - refraction of light has not!
This is a property of the underlying mathematical equations describing
the physical effects and therefore you can't overcome this by more
intelligent simulation techniques.
And if you don't believe this you can easily test it yourself BTW - the
VFAQ mentions how: Replace your single object with a lot of smaller
ones with slightly different IOR. This will give you a realistic
impression of the quality of results and the rendering speed of such a
simulation.
Christoph
--
POV-Ray tutorials, include files, Landscape of the week:
http://www.imagico.de/ (Last updated 31 Oct. 2005)
MegaPOV with mechanics simulation: http://megapov.inetart.net/
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Chambers nous apporta ses lumieres en ce 10/02/2006 20:29:
> I might ramble here, but anyway...
>
> Just thinking about variable IOR today, and I reread the section of the
> VFAQ on it. Basically, by specifying variable IOR as a property of
> media, the density of the media could be used to vary the IOR. By
> supersampling the media enough, it should be possible to get decently
> accurate images (even though they may take days or weeks to render {but,
> this has never stopped POVers before, has it?}). It should be even
> possible to get a more or less accurate derivative of the density
> function, and guess the correct length for the next ray segment.
>
> Anyway, however slow it is (again - has slowness ever stopped POVers
> before?), does anyone else think it might be time to try it out? Used
> properly, this would allow some great effects. Mostly, I'm thinking of
> subtle heat shimmers in landscape scenes - but I'm sure there are others.
>
> ...Chambers
You may try simulating that using merged, nested objects with progressively higher
iors. You need to
crank up the max_trace_level. You will get discontinuitys.
The best aproach is to modulate the curvature of the object or use normal
manipulation. Progressive
glasses use exactly that thecnique: the curve is NOT constant! The inside of the lense
get flater
over the area with higher strenght. You need an isosurface to acheive that.
In fact, you ONLY encounter intentional man-made variable ior in fiber optiques. In
nature, you find
it in the athmosphere and in heat induced turbulence in water and air (like in and
over a flame).
--
Alain
-------------------------------------------------
But I thought YOU did the backups...
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IMHO, would it not be possible to simulate a sphere of continually
increasing ior towards its centre? If a ray intersects the sphere close to
90 degrees to the normal the ior is low because the air is very thin on the
outside. As the angle of intersection gets closer to the circle's normal the
ior increases because going towards the centre the ior increases. I think
this would be the first step in the right direction.
-Nekar Xenos-
--
The truth is out there...
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Nekar Xenos <go_### [at] yahoo com> wrote:
> IMHO, would it not be possible to simulate a sphere of continually
> increasing ior towards its centre? If a ray intersects the sphere close to
> 90 degrees to the normal the ior is low because the air is very thin on the
> outside. As the angle of intersection gets closer to the circle's normal the
> ior increases because going towards the centre the ior increases. I think
> this would be the first step in the right direction.
If there is an object inside that sphere, how would you calculate where
this curved line intersects that object?
--
- Warp
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"Warp" <war### [at] tagpovrayorg> wrote in message
news:43fb7e4b@news.povray.org...
> If there is an object inside that sphere, how would you calculate where
> this curved line intersects that object?
>
How about taking the ray on a circular path in one direction as the ior goes
up and changing the direction when the ior goes down resulting in an
s-shaped path.
-Nekar Xenos-
--
"The truth is out there..."
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Nekar Xenos <go_### [at] yahoocom> wrote:
> > If there is an object inside that sphere, how would you calculate where
> > this curved line intersects that object?
> How about taking the ray on a circular path in one direction as the ior goes
> up and changing the direction when the ior goes down resulting in an
> s-shaped path.
What? Did you even understand my question?
--
- Warp
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"Warp" <war### [at] tagpovrayorg> wrote in message
news:44002edb@news.povray.org...
> Nekar Xenos <go_### [at] yahoocom> wrote:
>> > If there is an object inside that sphere, how would you calculate
>> > where
>> > this curved line intersects that object?
>
>> How about taking the ray on a circular path in one direction as the ior
>> goes
>> up and changing the direction when the ior goes down resulting in an
>> s-shaped path.
>
> What? Did you even understand my question?
>
> --
> - Warp
I meant to replace my intitial suggestion with the second one. Is it not
possible to test intersection of a circle with an object? Please excuse me,
but I (obviosly)don't know how a raytracer is programmed. How is
intersection of a straight ray done? I was thinking of just replacing the
formula for the straight ray with the formula of a circle.
--
-Nekar Xenos-
----------------------------------------
"The truth is out there..."
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Nekar Xenos <go_### [at] yahoocom> wrote:
> I meant to replace my intitial suggestion with the second one. Is it not
> possible to test intersection of a circle with an object? Please excuse me,
> but I (obviosly)don't know how a raytracer is programmed. How is
> intersection of a straight ray done? I was thinking of just replacing the
> formula for the straight ray with the formula of a circle.
How would a ray travelling in a circular path be any feasible way of
emulating variable ior? I'm not even sure it's physically possible to
have an object with an ior such that light travels in a circular path
through it regardless of the direction.
--
- Warp
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Warp nous apporta ses lumieres en ce 25/02/2006 06:50:
> Nekar Xenos <go_### [at] yahoocom> wrote:
>
>>I meant to replace my intitial suggestion with the second one. Is it not
>>possible to test intersection of a circle with an object? Please excuse me,
>>but I (obviosly)don't know how a raytracer is programmed. How is
>>intersection of a straight ray done? I was thinking of just replacing the
>>formula for the straight ray with the formula of a circle.
>
>
> How would a ray travelling in a circular path be any feasible way of
> emulating variable ior? I'm not even sure it's physically possible to
> have an object with an ior such that light travels in a circular path
> through it regardless of the direction.
>
Gravity lense, in any direction not directly aimed at it's center. As those don't have
a deffinite
center (each constituent object been a "center"), ray's paths looks rather like a
drunken man path.
Note to self: I need to create such a lense in POV-Ray one day.
--
Alain
-------------------------------------------------
After any salary raise, you will have less money at the end of the month than you did
before.
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