I wanted to use sphere_sweep to generate a scalled torus, like 
  torus { 10,5 scale <4,1,1> 
*but* I wanted it's section to be a circle (and not to get deformed) 
- so I wanted an cylinder wrapped into elipse shape.

But usig sphere sweep didnt help:
  http://www.raf256.com/3d/torus_as_spline.jpg

as we see in "yellow" segment - section is deformed.

is this a bug or a is this expected behaviour of sphere_sweep?

Sweep is build from points spaced equaly along scalled torus shape:

  sphere_sweep {
    linear_spline  //cubic_spline 
    #local E=45/4; // precission
    (360/E)+3
    #local I=-E; #while (I<=360+E)
      vrotate(<0,0,Major>, <0,I,0>)*Scale, Minor
    #local I=I+E; #end
  }

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On 6 May 2003 13:52:05 -0400, "Rafal 'Raf256' Maj" <raf### [at] raf256com> wrote:
> I wanted to use sphere_sweep to generate a scalled torus, like 
>   torus { 10,5 scale <4,1,1> 
> *but* I wanted it's section to be a circle (and not to get deformed) 
> - so I wanted an cylinder wrapped into elipse shape.
>
> But usig sphere sweep didnt help:
>   http://www.raf256.com/3d/torus_as_spline.jpg

First of all your filename shows that you do not understand that torus can't be
spline. Spline is not object. Sphere_sweep is not spline.

> as we see in "yellow" segment - section is deformed.

Is top object viewed from top ? Then presented crossection is what you asked
for. Think about it.

If I understand your intentions corectly the only ideal solution here is some
playing with functions and using it in isosurface.

ABX

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> as we see in "yellow" segment - section is deformed.

The sphere sweep is correct. Every point on the surface of the sphere sweep
is an equal distance from the nearest point on the sphere sweep's spline.
Note that said point on the spline may not be within the yellow box you
created.

 - Slime
[ http://www.slimeland.com/ ]

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"Rafal 'Raf256' Maj" <raf### [at] raf256com> wrote in 
news:Xns### [at] 204213191226:

> I wanted to use sphere_sweep to generate a scalled torus, like 
>   torus { 10,5 scale <4,1,1> 
> *but* I wanted it's section to be a circle (and not to get deformed) 
> - so I wanted an cylinder wrapped into elipse shape.
> 
> But usig sphere sweep didnt help:
>   http://www.raf256.com/3d/torus_as_spline.jpg
> 
> as we see in "yellow" segment - section is deformed.
> 
> is this a bug or a is this expected behaviour of sphere_sweep?
> 
> Sweep is build from points spaced equaly along scalled torus shape:
> 
>   sphere_sweep {
>     linear_spline  //cubic_spline 
>     #local E=45/4; // precission
>     (360/E)+3
>     #local I=-E; #while (I<=360+E)
>       vrotate(<0,0,Major>, <0,I,0>)*Scale, Minor
>     #local I=I+E; #end
>   }


Try this Rafal:

#declare Major = 5.0;
#declare Minor = 1.5;
#declare Scale = <3.0, 1.0, 0.5>;

difference {
  union {
    #declare I = 0;
    #while (I < 360)
      sphere { Scale*vrotate(Major*z, I*y), Minor }
      #declare I = I + 1;
    #end // while  
    pigment { color rgb <1, 1, 1> }
  }
  plane { z, 0 pigment { color rgb <1, 1, 0> } }
}

camera { location -30*z look_at 0*y }
light_source { <1, 4, -4>*100 color rgb <1, 1, 1> shadowless }
background { color rgb <0.5, 0.5, 1> }


Tor Olav

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