On 2/11/2015 3:04 AM, Le_Forgeron wrote:
> Le 11/02/2015 04:13, Mike Horvath a écrit :
>> Has anyone written a function for a caternaroid(?) that works just like
>> Paraboloid_Z in shapes_old.inc?
>
> I'm afraid not: Paraboloid_Z is a quadric, but a caternaroid (do you
> mean something like a Pringles) would need something like cosh in the
> equation.
>
> http://bennbatt.tumblr.com/
>
>   z = A.cosh(x) - B.cosh(y)
>
> Now, I might just be wrong, because the displayed equation
>
> z = x²/a² -y²/b² with x²/a²+y²/b² < 1 would be something easy on a
> quartic, with intersection of a cylinder along z for the <1 part.
>
> // create a quadratic (2nd order) infinite polynomial surface
> quadric {
>    <1, -1, 0> //  A x^2  + B y^2  + C z^2  +
>    <0, 0, 0> //  D xy   + E xz   + F yz   +
>    <0, 0, -1> //  G x    + H y    + I z    +
>    0         //  J
> }
>
>


Sorry. I meant a caternary surface of revolution. Looks almost like 
Paraboloid_Z, but a little bit different. Thanks.

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