I had some strange rendering problemsw hen rendering a scene with an
object like this :
#declare MyObject1 = difference {
  cylinder { <0.0,-0.07, 0.0>, <0.0, 0.07, 0.0>, 85.935 }
  cylinder { <0.0,-1.00, 0.0>, <0.0, 1.00, 0.0>, 85.815 }
}

It looks like someone has cut some part of the 'sides' of the cylinder.
The endcaps are O.K., but it looks like two disks instead of a solid
ring.

This object is used within a pretty complex CSG, but the same problem
exists when rendering the object on its own.

When the ratio of radius to hight is > +/- 500, the problem disapears.
I had to solve this by using a higher cylinder and cutting the ring with
a plane :

#declare MyObject2 = difference {
  cylinder { <0.00,-0.07, 0.00>, <0.00, 5.00, 0.00>, 85.935 }
  cylinder { <0.00,-1.00, 0.00>, <0.00, 6.00, 0.00>, 85.815 }
  plane { y, -0.07 }
}

It should be seen with a little scene like this :

camera {
  location <-0.5, 0.5, 0.5>
  look_at <0.0, 0.0, 0.0>
}

light_source {
  <-5.0, 5.0, 5.0>
  color rgb <1.0, 1.0, 1.0>
}

object { MyObject1      //PROBLEMS !!!!!
// object { MyObject2     //PROLBLEM SOLVED !!!!!
  pigment { color rgb <1.0, 1.0, 0.5> }
  transform -85.875*y
}

Post a reply to this message

What a mistake to make :

When the ratio of radius to hight is < (SMALLER !!!) +/- 500 the problem
disapears.

Wouter Depuydt schreef:
> 
> I had some strange rendering problemsw hen rendering a scene with an
> object like this :
> #declare MyObject1 = difference {
>   cylinder { <0.0,-0.07, 0.0>, <0.0, 0.07, 0.0>, 85.935 }
>   cylinder { <0.0,-1.00, 0.0>, <0.0, 1.00, 0.0>, 85.815 }
> }
> 
> It looks like someone has cut some part of the 'sides' of the cylinder.
> The endcaps are O.K., but it looks like two disks instead of a solid
> ring.
> 
> This object is used within a pretty complex CSG, but the same problem
> exists when rendering the object on its own.
> 
> When the ratio of radius to hight is > +/- 500, the problem disapears.
> I had to solve this by using a higher cylinder and cutting the ring with
> a plane :
> 
> #declare MyObject2 = difference {
>   cylinder { <0.00,-0.07, 0.00>, <0.00, 5.00, 0.00>, 85.935 }
>   cylinder { <0.00,-1.00, 0.00>, <0.00, 6.00, 0.00>, 85.815 }
>   plane { y, -0.07 }
> }
> 
> It should be seen with a little scene like this :
> 
> camera {
>   location <-0.5, 0.5, 0.5>
>   look_at <0.0, 0.0, 0.0>
> }
> 
> light_source {
>   <-5.0, 5.0, 5.0>
>   color rgb <1.0, 1.0, 1.0>
> }
> 
> object { MyObject1      //PROBLEMS !!!!!
> // object { MyObject2     //PROLBLEM SOLVED !!!!!
>   pigment { color rgb <1.0, 1.0, 0.5> }
>   transform -85.875*y
> }

Post a reply to this message

I didn't find anything wrong. Your example Object2 to correct the
supposed problem is wrong. At least it isn't the same as the Object1,
since it is leaving the upper y (wider section) instead of doing what
the first seems to be intended to do.
May just be your perspective of the shape and thinking of it
incorrectly. You simply have a very thin cylinder, very short in height
and large in diameter. To get the same for Object2 you would need a
plane {-y,-0.07} not what you have there. Hope this is right anyway, I
lost my first message reply.


Wouter Depuydt wrote:
> 
> What a mistake to make :
> 
> When the ratio of radius to hight is < (SMALLER !!!) +/- 500 the problem
> disapears.
> 
> Wouter Depuydt schreef:
> >
> > I had some strange rendering problemsw hen rendering a scene with an
> > object like this :
> > #declare MyObject1 = difference {
> >   cylinder { <0.0,-0.07, 0.0>, <0.0, 0.07, 0.0>, 85.935 }
> >   cylinder { <0.0,-1.00, 0.0>, <0.0, 1.00, 0.0>, 85.815 }
> > }
> >
> > It looks like someone has cut some part of the 'sides' of the cylinder.
> > The endcaps are O.K., but it looks like two disks instead of a solid
> > ring.
> >
> > This object is used within a pretty complex CSG, but the same problem
> > exists when rendering the object on its own.
> >
> > When the ratio of radius to hight is > +/- 500, the problem disapears.
> > I had to solve this by using a higher cylinder and cutting the ring with
> > a plane :
> >
> > #declare MyObject2 = difference {
> >   cylinder { <0.00,-0.07, 0.00>, <0.00, 5.00, 0.00>, 85.935 }
> >   cylinder { <0.00,-1.00, 0.00>, <0.00, 6.00, 0.00>, 85.815 }
> >   plane { y, -0.07 }
> > }
> >
> > It should be seen with a little scene like this :
> >
> > camera {
> >   location <-0.5, 0.5, 0.5>
> >   look_at <0.0, 0.0, 0.0>
> > }
> >
> > light_source {
> >   <-5.0, 5.0, 5.0>
> >   color rgb <1.0, 1.0, 1.0>
> > }
> >
> > object { MyObject1      //PROBLEMS !!!!!
> > // object { MyObject2     //PROLBLEM SOLVED !!!!!
> >   pigment { color rgb <1.0, 1.0, 0.5> }
> >   transform -85.875*y
> > }

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