> Hello yet again,
>
> I've been toying with my ascending spiral for a long time now, and I believe I'm
> achieving some good results, finally. Actually, thanks to you guys, of course.
>
> Anyway, Although I tried it a million different ways, I'm still getting
> artifacts, and I don't see a way to get rid of the problem.
>
> So, I started to wonder if there is a way to transform my ascending spiral into
> an isosurface. A parametric isosurface would be even better. And if there is a
> way to transform a blob straight into a mesh, that would be simply perfect. Here
> is a post to the images forum, so you can see the spiral:
>
http://news.povray.org/povray.binaries.images/thread/%3Cweb.4bc8bcc516734c1270e596300%40news.povray.org%3E/
>
> I got it by way of a cylinder blob with some 10,000 cylinders, and still those
> pesky artifacts remain. All I want is to make it completely smooth, and keep it
> "renderable" with my meager equipment.
>
> Thanks once again,
>
> Ruy
>
>

After some testing, my best result is with the following:

#declare Radius = 42;
isosurface{
	function{f_spiral(x,
y/45-sqrt(pow(x,2)+pow(z,2))/30,
z,
  7, // The spacing between turns.
  0.12, // Controlls the thickness of the ribon. Keep small.
  Radius, // How large
  0, 0, // 2 throw away parameters
  0.06)} // Controls the shape. Almost square but slightly rounded.
	contained_by{box{<Radius,-3,Radius><-Radius,Radius/2,-Radius>}}
	threshold 0
	max_gradient 20
	all_intersections // As it is transparent, you need it.
	pigment{cylindrical // for the colour.
		color_map{[0 rgbf<0.01,0.01,1,Filter>][0.25 
rgbf<0.01,1,1,Filter>][0.50 rgbf<0.01,1,0.01,Filter>][0.75 
rgbf<1,1,0.01,Filter>][1 rgbf<1,0.01,0.01,Filter>]}
		scale Radius} //Adjust to the overall size.
	finish{specular 0.7 roughness 0.001 reflection{0.001, 0.6 
fresnel}conserve_energy ambient 0 diffuse 0.8}
	interior{ior 1.4}
	}

"y/45" effectively act as "scale<1,45,1>". It controlls the width of the 
ribon as well as the overall height of the spiral.
"-sqrt(pow(x,2)+pow(z,2))/30" controlls how fast the spiral climb. 
Adjust "/30" to change the rate of ascention. SMALL = steep, LARGE = 
slow climb.
You can declare the colours of the color_map any way you want. You can 
hace up to 255 entries, but don't need as many.


Alain

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