// create a curved tube object translating a sphere along a certain path
sphere_sweep {
  linear_spline                 // linear curve
  //cubic_spline                // alternative spline curves
  //b_spline
  4,                            // number of specified sphere positions
  <-5, -5, 0>, 1                // position, radius
  <-5, 5, 0>, 1                 // ...
  < 5, -5, 0>, 1
  < 5, 5, 0>, 1
  //tolerance 0.001             // optional
}