sphere_sweep
// 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
}