Here is an image for a post I submitted where I have two superposed boxes with
different refractive indices.  The bottom region should be clear and the top
liquid should be a translucent yellow.  At the top of the upper region there
seems to be a weird line.  Also, there are weird triangles formed.  I do not
think these are all real.  I have overlapped the two regions a tiny bit and
used the merge operator (this seems to work the best).  I also have the bottom
region intersecting a plane (the floor) at the bottom to make things look
better (as from previous advice from this forum).  I have turned diffuse and
roughness to zero to try to mimic real life (they are supposed to be liquids),
but playing with them did not seem to fix the artifacts anyway.  I have posted
the code in the general section where I have reposted the problem.

Any Ideas,
Mike

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On Tue, 24 Feb 2009 18:33:02 -0500, Mike wrote:

>   The bottom region should be clear and
> the top liquid should be a translucent yellow.  At the top of the upper
> region there seems to be a weird line.  Also, there are weird triangles
> formed.

Just looking at the images myself, the reflections look right to me - I 
*think* you get the weird lines because of reflections off the bottom, 
but because of the IOR settings, you don't see (for example with the 
little triangle at the bottom) the reflection in the side because of the 
IOR.

I haven't looked at the model myself, just my first impressions on 
looking at the image were "this looks right to me assuming the IOR is set 
to do that".  I vaguely recall seeing something like this IRL that had 
reflections that were similar.

Jim

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Hi Mike,

looks all perfectly ok to me (well, admittedly it does *look* weird, but
refractions occasionally do).

So far, I didn't find any feature in the image that couldn't be explained. In
fact, I'm actually *missing* two lines. See the annotated shot (the red dots
mark the refracted images of the top box's lower rear left corner; the red
circle marks where I'd have expected another refracted images of that corner.

A possible explanation for these missing lines might be that the angle of
incidence on the left wall (seen through the top wall) is just shallow enough
to result in total (i.e. 100%) reflection.

There are some more subtle lines I didn't bother to try to explain. I suspect
these are secondary or even tertiary reflections & refractions, or color bands
due to the output format used.

To get a better feeling for the effects that can be observed in the image, you
may want to do an animation of this scene, with the camera circling around.
This may help you grasp what's going on.

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