//--------------------------------------------------------------------------
#declare N_Waves = 3; // number of waves per unit y !
isosurface { //-------------------------------------------------------------

  function { sin( N_Waves*y*2*pi   ) /11
             + sqrt(x*x*N_Waves + z*z*N_Waves ) 
             - 0.9 //  2* radius ? 
           }
  threshold 0
  contained_by {box {<-1,0,-1>, < 1, 2, 1>}}
  max_gradient 10
  accuracy 0.005
  open  // optional

         texture { pigment{ color rgb< 1.0, 0.7, 0.1> } //  deep yellow 
                // normal { bumps 0.5 scale 0.05 }
                   finish { phong 1 reflection 0.00}
                 } // end of texture 

  scale <1,1,1>
  rotate <0, 0, 0>
  translate < 0,0, 0>
} // end of isosurface -----------------------------------------------------