On 03/04/2025 04:27, yesbird wrote:
> 
> Thanks for advice, as I said in my previous post, there are a lot of
> 'ready-to-use' solutions ...
>

And Povray is no exception :).
In attachment is MathView vision of this canonical example:

// --------------------------------------- parametric surface -------------
#declare a = 1.0;                       // conical spiral
#declare b = 8;
#declare c = 0.2;
#declare n = 5;
parametric{
  function { a*(1-0.5*v/pi)*sin(n*v+0.5*pi)*(1-cos(u))
             + c*sin(n*v+0.5*pi) }
  function { b*0.5*v/pi + a*(1-0.5*v/pi)*sin(u) }
  function { a*(1-0.5*v/pi)*cos(n*v+0.5*pi)*(1-cos(u))
             + c*cos(n*v+0.5*pi) }
   <0,0>,<2*pi,2*pi>  // start, end of (u,v)
   contained_by {box {<-1,-1,-1>*2*pi,<1,b/3,1>*2*pi}}
   max_gradient 8  // better but slower: 10
   accuracy 0.01 // better but slower: 0.001 or smaller
   precompute 10 x,y,z
   texture{ pigment{ color rgb<1,1,1>}
            finish { phong 0.5}}
   scale 0.125
   rotate <0, 90, 0>
} // end of parametric 
----------------------------------------------------
-- 
YB

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