re cylinder and ray sketch rotate so cylinder axis is z axis intersect x y projection of line with projected cylinder similar to but easier than sphere intersection result no intersection one intersection or two intersections parameterized along line by t and t now look at z and compute intersections of line with top and bottom planes of cylinder this gives t and t the interval of intersection is then the bit of the line from t t intersect t t details left as an exercise for the reader s spencer w thomas info tech and networking b cfob genome informatician univ of michigan ann arbor mi spencer w thomas med umich edu fax
