Yes. an ellipse drawn on the eyeline, with no other information, means we’re looking directly at an ellipse (as opposed to a circle tilted in perspective). If it’s drawn as part of a cylinder, it will depend on which plane is closest to us.
– If it’s the top plane, it’s leaning toward us (imagine a cylinder trying to give you a hug).
– If it’s the bottom plane, it’s leaning away from us (imagine you pushed the cylinder away).
– If it’s the side plane, it means we’re looking at something in the middle (imagine a Roman column).
The center line is used to orient the ellipse correctly. The axes will be 90 degrees to each other. This will help with complex constructions.
Drawing circles within the cylinder shows the cross contours. The farther side of a cylinder will be more rounded than the closer side.