Warp nous apporta ses lumieres en ce 14/02/2006 09:42:
> Florian Brucker <tor### [at] torfboldcom> wrote:
> 
>>Thanks for your opinions about that. I hadn't considered that from a 
>>mathematical point of view a degenerate cylinder is troublesome 
>>(although, from a user's point of view it may not be).
> 
> 
>   The problem is simply that if the endpoints of the cylinder are the
> same point but the cylinder has a non-zero radius, POV-Ray cannot know how
> to orientate the resulting disc.
> 
>   Basically there doesn't exist degenerate spheres (the only exceptional
> case is a sphere with a radius of 0, but that's just no sphere at all)
> or degenerate boxes (creating an infinitely thin "box" is umambiguous
> and thus there's no problem). However, a cylinder with a non-zero radius
> but with coincident endpoints is a problem because it can't be created
> unambiguously.
> 
It's obvious that in that case, the axis of the cylinder is undefined: it's impossible
to know it's 
orientation. You have a few options:
- ignore the object. Don't draw it and issue a warning or a non-fatal error.
- "assume" it's a sphere of the defined radius. Issue a warning about the
"asumption"/conversion. 
This is somewhat similar to scale 0.
- throw a fatal error and abort the render.


-- 
Alain
-------------------------------------------------
Change is inevitable, except from vending machines.

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