Takuya Arai wrote:
> 
> I posted this to comp.graphics.rendering.raytracing but I thought I'd post
> this here too.
> 
> I have a really basic question of how POVRay handles light going through a
> transparent object.  For example, say I made a chunk of rock with some edges
> so it has a vaguely crystal look and made it into a reddish ruby color and
> transparent (or translucent...can't remember the proper term).
> 
> Obviously POVRay will calculate the index of refraction of the light going in.
> I think you can change that too.  However, my question is, how does POVRay
> calculate the thickness?  If the rock is hollow in the middle then the light
> wouldn't bend as much when it shines through as it would if it was solid.
> Does POVRay assume it's a solid?  Is it dependent on something?  It's really
> not that big of a deal but I'd like to know more for the academic standpoint
> for now.
> 
> I made a quick and dirty render.  Essentially a sword in a stone type thing
> and made the stone that ruby chunk so I can see the tip of the sword inside
> the rock.  Obvioulsy there's distortion because of the ridges on the outside
> of the ruby but I'm wondering just how accurate the bending of the blade is.
> If you want, it's at:
> 
> http://members.stratos.net/tima/images
> 
> and it's the file swordinstone.jpg
> 
> Anyway, if any of you can shed some light on this subject, I'd really
> appreciate it.  If you reply to this, please also send me a copy via e- mail
> since I dont' read this group too often.
> 
> Thank you in advance for any help.
> 
> Tim
> 

 Think of it this way. If you have a standard POV-Ray box primitive and
apply an ior value to it Pov will treat it as a solid object. If we take
an example of a box created by six individual pieces, each with a known
thickness, then apply and ior value to it, Pov will handle the index of
refraction of each panel of the box but not the center of it. A good
example of this would be a drinking glass. It is a solid material where
the outer glass portion is, but the inside is hollow, where the liquid
goes. Pov will calculate the ior for the glass but not the hollow space
between it's walls.
  In the case of your "sword in a stone" Pov appears to be handling it
as one solid object which I presume is what you want. If you intentionally
hollowed out the inside of the stone and gave it's walls a finite thickness
the sword itself would appear differently in different areas of the stone.

-- 
Ken Tyler

See my 1000+ Povray and 3D Rendering and Raytracing Links at:
http://home.pacbell.net/tylereng/index.html

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