"Francesco" <nas### [at] gmailcom> wrote:
> I need to generate only a portion of an ellipsoid (a surface, not a solid). The
> best way to proceed is by declaring it as a difference between an ellipsoid and
> a box?

It seems to me I need to use isosurface. I am studying them :)

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Le 03.11.2007 12:08, Francesco nous fit lire :
> "Francesco" <nas### [at] gmailcom> wrote:
>> I need to generate only a portion of an ellipsoid (a surface, not a solid). The
>> best way to proceed is by declaring it as a difference between an ellipsoid and
>> a box?
> 
> It seems to me I need to use isosurface. I am studying them :)

Which portion of an ellipsoid do you need ?

If it's a 2D surface, intersection with a couple of parallele plane
should be fine.
Or direct usage of an ellipse.

If it's part of the 3D surface, it obviously depend on which part of
the ellipsoid you want.
CSG is one way.
Parametric another.
And isosurface also... as well as meshes, smooth triangles and so on.

-- 
The superior man understands what is right;
the inferior man understands what will sell.
-- Confucius

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Francesco wrote:
> "Francesco" <nas### [at] gmailcom> wrote:
>> I need to generate only a portion of an ellipsoid (a surface, not a solid). The
>> best way to proceed is by declaring it as a difference between an ellipsoid and
>> a box?
> 
> It seems to me I need to use isosurface.

No, why? CSG is the way to go.

	Thorsten

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Thorsten Froehlich <tho### [at] trfde> wrote:

> No, why? CSG is the way to go.
>
>  Thorsten

It seemed to me CSG was for solid construction, while I need a curve surface
(generated by an ellipse).

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Wasn't it Francesco who wrote:
>I need to generate only a portion of an ellipsoid (a surface, not a solid). The
>best way to proceed is by declaring it as a difference between an ellipsoid and
>a box? Thanks in advance for help. I am trying to learn by myself but I am
>afraid it will require a lot of time, so any help is useful.

Using a difference makes it look like a solid rather than a surface. Try
clipped_by instead of difference.

Note that you can make an ellipsoid by scaling a sphere.

sphere {0,2
  scale <2,1,0.5>
  clipped_by {box {<-5,-5,-0.2><5,5,0.7>}}
  pigment {rgb 1}
}

-- 
Mike Williams
Gentleman of Leisure

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Le Forgeron <jgr### [at] freefr> wrote:
> Le 03.11.2007 12:08, Francesco nous fit lire :
> > "Francesco" <nas### [at] gmailcom> wrote:
> >
> > It seems to me I need to use isosurface. I am studying them :)
>
> Which portion of an ellipsoid do you need ?
>
> If it's a 2D surface, intersection with a couple of parallele plane
> should be fine.
> Or direct usage of an ellipse.
>

I would design a curve surface generated by 1/4 ellipse rotating for 10 degrees.

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Wasn't it Francesco who wrote:
>
>I would design a curve surface generated by 1/4 ellipse rotating for 10 degrees.

Perhaps something like this

sphere {0,1
  scale <2,1,1>
  clipped_by {plane {-y,0}}
  clipped_by {plane {z,0}}
  clipped_by {plane {-z,0} rotate <0,10,0>}
  pigment {rgb 1}
}


-- 
Mike Williams
Gentleman of Leisure

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Mike Williams <nos### [at] econymdemoncouk> wrote:
> Perhaps something like this
>
> sphere {0,1
>   scale <2,1,1>
>   clipped_by {plane {-y,0}}
>   clipped_by {plane {z,0}}
>   clipped_by {plane {-z,0} rotate <0,10,0>}
>   pigment {rgb 1}
> }

That is exactly what I was trying to do! Thanks a lot Mike :)) Simple and
powerful commands. Just a question: you make rotating the clipping plane in
order to exclude some parts to the cut. Is it right?

Francesco

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Wasn't it Francesco who wrote:
>Mike Williams <nos### [at] econymdemoncouk> wrote:
>> Perhaps something like this
>>
>> sphere {0,1
>>   scale <2,1,1>
>>   clipped_by {plane {-y,0}}
>>   clipped_by {plane {z,0}}
>>   clipped_by {plane {-z,0} rotate <0,10,0>}
>>   pigment {rgb 1}
>> }
>
>That is exactly what I was trying to do! Thanks a lot Mike :)) Simple and
>powerful commands. Just a question: you make rotating the clipping plane in
>order to exclude some parts to the cut. Is it right?

You said you wanted a quarter ellipse rotated through 10 degrees. So I
made one cut at 0 and one cut at 10 degrees.

Actually, it would look more symmetrical if you make the cuts at -5 and
+5 degrees

sphere {0,1
  scale <2,1,1>
  clipped_by {plane {-y,0}}
  clipped_by {plane {z,0} rotate <0,-5,0>}
  clipped_by {plane {-z,0} rotate <0,5,0>}
  pigment {rgb 1}
}

-- 
Mike Williams
Gentleman of Leisure

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Mike Williams <nos### [at] econymdemoncouk> wrote:
> You said you wanted a quarter ellipse rotated through 10 degrees. So I
> made one cut at 0 and one cut at 10 degrees.
>

Ok, it's clear. Thanks again.

Francesco

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