Chris B nous apporta ses lumieres ainsi en ce 2004-11-12 09:25... :

>"Mike Thorn" <mik### [at] realitycheckmultimediacom> wrote in message
>news:4194a758$1@news.povray.org...
>  
>
>>Why do people often use planes (a huge
>>infinite object) to do CSG or create more complex geometrical figures?
>>Wouldn't it be easier in terms of size to use something a little
>>smaller, like a box?
>>
>>Or is rendering speed the answer?
>>    
>>
>
>I find it easier to visualise with planes. Particularly when you need to
>rotate and translate the cutting surface.
>If you use a box, then you need to be a bit careful about where all of the
>other faces of the box will end up after rotation and translation, otherwise
>you could end up with spurious offcuts, floating around where you don't want
>them to be.
>
>I don't know whether there's a speed difference. When I used CSG in a hair
>macro I used boxes to cut each hair as I assumed that they were more
>efficient than planes, but I don't know if that's true.
>
>
>  
>
As POV Ray don't try to bound a plane, when you subtract a plane from a 
finite object, the resulting bounding box would stay that of the first 
object. When using a box to do the same, the resulting bounding box tend 
to expand to the total combined size of both the cuted and the cuting 
shapes. This can lead to very large, almost empty bounding shapes.

Alain

Post a reply to this message