A helix cylinder is constructed by finding the least squares linear fit along the coordinates of the helix's C atoms. It is possible to pick the C for each cylinder segment, but they are at the location of the C , which is not near the axis cylinder.
Interesting results occur when the whole protein is defined to be a helix and drawn as a cartoon.
The solid beta ribbon is constructed by building a spline along the center points between each beta sheet residue. Again, the spline is linearly interpolated to find the start and end points for each residue. A ribbon segment is used if the corresponding C atom is selected. Note that since this method assumes the protein is in a beta conformation, it draws a much smoother ribbon than the standard Ribbon option, which draw the ribbon with an oscillation along the sheet. The other conformations are drawn as a tube.