Ok so I am doing an astronomical simulation. But that isn't the important part. I have two points defined in terms of spherical coordinates: an observatory, and the satellite it is tracking. They are labelled O and S respectively in the (bad) diagram at the below link (clicky). Converting them to 3D cartesian points is trivial. The cylinder seen is the field of view of the telescope (yes, I know it wouldn't really be a cylinder but work with me) The field of view is fixed. The observatory is the center point of the bottom 'cap' of the cylinder. I need to know what the point will appear as in the view as if there were a giant eyeball looking through the bottom cap. The output should be, of course, a circle. So how do I go about projecting a point in this cylinder? http://allyoucanupload.webshots.com/v/2001475849017047214"