I made a refraction test and I'm a bit confused.

  For the test, I made a typical glass-container-with-water object in three
different ways:
  1. The water cylinder is just a bit smaller than the inner surface of the
glass cylinder.
  2. The water cylinder is just a bit bigger than the inner surface of the
glass cylinder.
  3. The glass cylinder has no inner surface (it's just like a solid object);
the glass cylinder is just inside it.

  One could think that at least 1 and 2 will produce a quite similar object.
However, the difference between them is very noticeable (see image). The
third case looks almost like the second one (except that the color of the
water is less filtered by the color of the glass). Notice also how the
top of third glass cylinder refracts the water more than the other two
(although this may be due to the max_trace_level).

  Why this difference between 1 and 2? Which of the three is the most
physically accurate?
  At least to me the first one looks the best (but I don't know if it's
the most realistic, physically speaking).

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Attachments:
Download 'glasstest.jpg' (60 KB)

Preview of image 'glasstest.jpg'

In article <38b027d7@news.povray.org>, Nieminen Juha 
<war### [at] sarakerttunencstutfi> wrote:

>   I made a refraction test and I'm a bit confused.
> 
>   For the test, I made a typical glass-container-with-water object in 
>   three
> different ways:
>   1. The water cylinder is just a bit smaller than the inner surface of 
>   the
> glass cylinder.
>   2. The water cylinder is just a bit bigger than the inner surface of 
>   the
> glass cylinder.
>   3. The glass cylinder has no inner surface (it's just like a solid 
>   object);
> the glass cylinder is just inside it.

I am guessing the first one simulates a thin film of air between the 
liquid and the glass, you can see this effect in real life, sometimes in 
conditions where a liquid does not wet it's container, sometimes in 
layered structures(like fingernails or some plastics) that are splitting 
apart. You can see some total internal reflection which bounces the rays 
out of the glass.
The second one looks like the liquid is actually contacting the glass. 
The third one acts like the liquid is actually part of the glass. This 
is probably the least realistic, the other two depend on what you are 
doing.

-- 
Chris Huff
e-mail: chr### [at] yahoocom
Web page: http://chrishuff.dhs.org/

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Nieminen Juha wrote:

>  I made a refraction test and I'm a bit confused.
>
So am I, not because of your test, but for some reason your postings with 
an attatched picture only load for ~80%. Then the downloading stops.

I did simmilar tests some time ago and fount #2 the most realistic. #3 
looks like massive glass. In #1 the air gap, however small, always looks 
big and unnatural, probably beacuse of the extra reflections.

When using photons, #2 is the best. The other two show less caustics. Also 
the overlap of water and glass make a difference, the smaller the better.

Ingo

-- 
Photography: http://members.home.nl/ingoogni/
Pov-Ray    : http://members.home.nl/seed7/

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The first one has a layer of air with different IOR than the glass or liquid,
thus bending the light differently.
The second one goes straight from glass to liquid and is physically accurate.
The third one is the wrong color because there is less filtering happening in the
glass.

--
___     ______________________________________________________
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"Nieminen Juha" <war### [at] sarakerttunencstutfi> wrote in message
news:38b027d7@news.povray.org...
|   I made a refraction test and I'm a bit confused.
|
|   For the test, I made a typical glass-container-with-water object in three
| different ways:
|   1. The water cylinder is just a bit smaller than the inner surface of the
| glass cylinder.
|   2. The water cylinder is just a bit bigger than the inner surface of the
| glass cylinder.
|   3. The glass cylinder has no inner surface (it's just like a solid object);
| the glass cylinder is just inside it.
|
|   One could think that at least 1 and 2 will produce a quite similar object.
| However, the difference between them is very noticeable (see image). The
| third case looks almost like the second one (except that the color of the
| water is less filtered by the color of the glass). Notice also how the
| top of third glass cylinder refracts the water more than the other two
| (although this may be due to the max_trace_level).
|
|   Why this difference between 1 and 2? Which of the three is the most
| physically accurate?
|   At least to me the first one looks the best (but I don't know if it's
| the most realistic, physically speaking).

A cross between #1 and #2 I'd believe, so I see what you mean; I don't see how
that would be possible to do.

Bob

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I can only say that the one in the middle is affected by
the reflections etc from the ones either side, and the 
camera angle doesn't help, the two outside images 
appear to be falling over.  

Having said all of this, just by looking at the pic, the 
one to the right looks the most realistic. 

-- 
Cheers
Steve              email mailto:sjl### [at] ndirectcouk

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