>>OK, I was about to post a question... but then I realised, I'm not sure
>>if the shape I'm looking for is a parabola or a hyperbola...
>>
>>Anyway, I was going to ask how I get POV-Ray to draw that shape. (The
>>one with two lobes that don't quite meet.) I thought it was in
>>shapes.inc somewhere, but I can't seem to find it...
> 
> 
> Hi,
> it's a hyperboloid

Ah, ok.

> the equation which describes it is:

> 
> where a,b,c determine the length/scaling of the axes.
> the axis with the plus-sign is at the same time the rotational axis

Excellent.

> in SDL you can make this with a quadric:
> #declare a=1;
> #declare b=2;
> #declare c=1;
> 
> quadric {
>   <-1/(a*a), 1/(b*b), -1/(c*c)>, //  A x^2  + B y^2  + C z^2  +
>   <0, 0, 0>,                     //  D xy   + E xz   + F yz   +
>   <0, 0, 0>,                     //  G x    + H y    + I z    +
>   -1                             //  J
>   texture {
>     pigment { color rgb 1 }
>     finish { diffuse 1 ambient 0 phong 0.5 }
>   }
> }
> 
> In this example the shape is symmetric about the y-axis
> and scaled by a factor of two.

I wanna use this to make the bottom of a glass. (That is, the glass is a 
cylinder, hollowed out with a hyperboliod.) Does the quadric primitive 
give an infinite shape? How would I position the "tip" of the shape at a 
particular point in space? (Say... where I want the inside of my glass 
to stop! ;-) )

Thanks for the info.
Andrew @ home.

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