Does anyone know how to perform CSG operations on flat objects.
I would like to do the following;

     difference{
          triangle {<0.7,0,1.6>,<-0.7,0,1.6>,<0,2.9,5.7>}//C
          triangle {<0.2,1.9,4.3>,<-.2,1.9,4.3>,<0,2.85,5.65>}  //front
cockpit
     }

and get the first triangle with the second cut out of it.

I think that the problem is that the two triangles are not coplanar.  Is

there any way to force this operation without having to recalculate the
second triangle to make it coplanar with the first? I have to do this
for about 70 triangles, and it sure would save time.

Thanks

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Jake Blanz wrote:
> 
> Does anyone know how to perform CSG operations on flat objects.
> I would like to do the following;
> 
>      difference{
>           triangle {<0.7,0,1.6>,<-0.7,0,1.6>,<0,2.9,5.7>}//C
>           triangle {<0.2,1.9,4.3>,<-.2,1.9,4.3>,<0,2.85,5.65>}  //front
> cockpit
>      }
> 
> and get the first triangle with the second cut out of it.
> 
> I think that the problem is that the two triangles are not coplanar.  Is
> 
> there any way to force this operation without having to recalculate the
> second triangle to make it coplanar with the first? I have to do this
> for about 70 triangles, and it sure would save time.
> 
> Thanks

<you will find this same answer on cgrr>

  If you read the POV-Ray docs under CSG and finite patch objects -

*****
There are six totally thin, finite objects which have no well-defined inside.
They are bicubic patch, disc, smooth triangle, triangle, polygon and mesh.
They may be combined in a CSG union but cannot be use in other types of CSG
difference, intersection, or merge (or inside a clipped_by statement). 
*****

-  you will find that it tell us that patch objects like bicubic patches and
triangles will not work in CSG operations. The reason for this is because they
do not have a clearly defined inside or outside which complicates determining
which surface of the triangle should be used in the CSG operation. While Pov
will try to do the operation correctly there is no gaurantee that it will work
as expected and in most case it will not work at all.
  In your case even if you do manage to make them co planer you would still
have a severe problem with coincident surfaces becuase you can not scale the
thickness of a triangle object. This means you are pretty much out of luck
with this type of operation.

Sorry :(



-- 
Ken Tyler -  1200+ Povray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/

Post a reply to this message

Jake Blanz wrote:

>Does anyone know how to perform CSG operations on flat
>objects. I would like to do the following;
>
>     difference{
>          triangle {<0.7,0,1.6>,<-0.7,0,1.6>,<0,2.9,5.7>}//C
>          triangle {<0.2,1.9,4.3>,<
>          -.2,1.9,4.3>,<0,2.85,5.65>}  //front 
>cockpit
>     }
>
>and get the first triangle with the second cut out of it.


If it is for this specific shape, you can make it with the 
polygon object.

Ingo

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

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