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On 1/8/2016 2:51 PM, Alain wrote:
> Le 16-01-08 13:24, Mike Horvath a écrit :
>> On 1/6/2016 12:48 AM, Mike Horvath wrote:
>>> How do I create a spiral tube, like a spring? Like this:
>>>
>>> http://www.f-lohmueller.de/pov_tut/animate/anim16e.htm
>>>
>>> but a single object, not a union of spheres?
>>>
>>> Thanks!
>>>
>>>
>>> Mike
>>
>> I found this parametric function online:
>>
>> http://math.stackexchange.com/questions/461547/whats-the-equation-of-helix-surface
>>
>>
>>
>> 1. How do I turn this into POV-Ray code?
>> 2. Can I fill this shape with a gas that is denser in the middle of the
>> tube and less dense at the tube's surface?
>>
>>
>> Mike
>
> You don't need to convert that parametric function.
>
> You can get that exact shape using f_helix1 or f_helix2 whitch are
> builtin function. Builtin functions are inheritently faster than user
> defined functions as they use compiled code.
>
> P0 is set to 1 to get only a single helix. Non integer may cause
> unexpected results. (not used if f_helix2)
> P1, P2 and P3 are renamed to reflect their functions.
> P4 elongate the section along the Y axis. Set to 1 to leave the shape
> unchanged. (not used if f_helix2)
> P5 is set to 1 whitch correspond to a circular section.
> 0 = square section.
> 1 = circular section
> 2 = losange section (I don't get it that a square rotated 45° could be
> called "diamond")
> >2 = concave losange section, may become degenarate if larger than 3.
> For a circular section, P6 have no effect. It rotate the section shape
> when it's not circular.
>
> Start with the following:
>
> f_helix1(x,y,z, 1, Period_per_unit, Minor_radius, major_radius, 1, 1, 0)
> or
> f_helix2(x,y,z, 0, Period_per_unit, Minor_radius, major_radius, 0, 1, 0)
>
> Both are designed for a threshold of zero. Evaluate as <0 inside, 0 at
> the surface and >0 outside.
> Negate the function used to use it to controll your media.
>
> Sample from i_internal.pov that you can find in the sample scenes (frame
> 26, frame 27 for f_helix2):
>
> #declare LCorner = <-1.5, -2.9, -1.5>;
> #declare RCorner = <1.5, 2.9, 1.5>;
> isosurface {
> function { f_helix1(x,y,z, 1, 8, 0.3, 0.9, 0.6, 0.2, 0) }
> //P0= number of helixes
> //P1= frequency
> //P2= minor radius
> //P3= major radius
> //P4= Y scale cross section
> //P5= cross section
> //P6= cross section rotation (¡)
> contained_by { box { LCorner, RCorner } }
> max_gradient 1.5
> texture { IsoTexture }
> no_shadow
> scale 1.9 rotate z*-54
> }
>
>
>
>
>
>
> Alain
The problem is that the isosurface is clipped within a box. This means
the edges of the cut are not perpendicular to the curve. It looks bad.
Mike
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