Threefoil knot

This is just clipped from a POV file I did to draw a knot

    //various constants


      uumin  = 0,uumax  = 4*pi


      vvmin  = 0,vvmax  = 2*pi


      a=1, b=0.3, c=0.5, d=0.3


    //preliminary calculations


      r=a+b*cos(1.5*uu)


      xx=r*cos(uu)


      yy=r*sin(uu)


      zz=c*sin(1.5*uu)      

             
      dx=-1.5*b*sin(1.5*uu)*cos(uu)-(a+b*cos(1.5*uu))*sin(uu)


      dy=-1.5*b*sin(1.5*uu)*sin(uu)+(a+b*cos(1.5*uu))*cos(uu) 


      dz=1.5*c*cos(1.5*uu)                    //Derivatives


      qn=vnormalize()            //Vector operatons


      qvn=vnormalize()


      ww=vcross(qn,qvn)


    //points and normals


      x1=xx+d*(qvn.x*cos(vv)+ww.x*sin(vv))  //Calculate the


      y1=yy+d*(qvn.y*cos(vv)+ww.y*sin(vv))  //points. ww.x is the 


      z1=zz+d*ww.z*sin(vv)                        //x value of ww vector


      nx1=qvn.x*cos(vv)+ww.x*sin(vv)          //Normals needed to


      ny1=qvn.y*cos(vv)+ww.y*sin(vv)          //make smooth triangles


      nz1=ww.z*sin(vv)

Here is the PoV3-source I used

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