It is important to recognize that objects that are circular in cross-section, such as a cylinder, will only be perfectly round when seen from above. How it is seen in most circumstances is more eliptical. The shape of the elipse is dictated by how it is tipped relative to our viewpoint. The closer to a topmost viewpoint will be closest to circular. When seen on edge of our viewpoint, it will be a straight line. All angles tipped between these two points will be somewhere in between. Use this information to learn how to see - and ultimately to see - the cylinders in your subject matter.