Many times when fabricating piping, round columns for structural applications, tanks, and other round items, it requires finding points at various degrees of position to one another. Obviously the first step in doing this is to find a reference point to start the layout from. The size of the item denotes the method of doing this in most cases. On tanks, it is likely that you will have a seam that runs linear to the tank body that you can use to locate position from the centerline of the tank. On many diameters of pipe, using a length of angle iron and laying it on the pipe so that the two legs of the angle are touching the pipe the length of it will give you an edge that you can draw a line the length of the pipe for reference.
The next step in this process requires determining the circumference of the round item. Generally wrapping a flat tape around the item and coming up with a measurement is a good first step. Once you have this done, use the number that you have, convert it to inches and a decimal and then divide this number by 360 to determine the running distance for each degree increment from the reference point.
Now if I needed to locate something 35 degrees from the reference line I would multiply the single degree increment by 35, and using the product from this equation, after converting it back to feet, inches, and a fraction, as required, I could measure from the reference line at each end of the round shape to mark two points, using a chalk line I could snap a line between these two points. I would then measure from the end of the round shape to the appropriate length or elevation and mark this point to locate whatever item belonged there. There are many variables to this process, I believe I've given folks a little bit to think about here and hopefully it will help some of you when facing this sort of scenario. Regards, aevald