Conic Spiral or Seashell

The basic seashell.

Parametric form:

      x=a*(1-v/(2*pi))*cos(n*v)*(1+cos(u))+c*cos(n*v) 
      y=a*(1-v/(2*pi))*sin(n*v)*(1+cos(u))+c*sin(n*v) 
      z=b*v/(2*pi)+a*(1-v/(2*pi))*sin(u)
Example:

a=0.2,b=1,c=0.1,n=2,u={ 0,2*pi},v={0,2*pi}

Twiddle constants to generate any conic spiral.

Here is the PoV3-source I used

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