Take a look at my "osgg" game, the buildin level editor does exactly this, and leaves you with a list of coordinates that it will happily write to a file for you. You might want to change a few lines of code to make it print out coordinates to screen while editing and to make it output in the desired format (it's raw text and there is a tiny bit of metadata that you could strip out).
https://github.com/DusteDdk/OsggFunny side note, I actually used the level editor to create the ship, base and enemy graphics in the game, so it was a bit chicken and egg, osgg was the main tool used to create osgg :P