   Relative roll pitch and yaw
  So I am working with a crappy engine (that I cannot change!) that utilizes roll pitch and yaw as the sole way to specify an entity's orientation in the world. I want to know how to convert relative roll pitch and yaw to world roll pitch and yaw. Here is an example: I have an aircraft at  rpy(45,0,45) and I want a camera pointing off this aircraft's nose at a depression of 45 degrees (pitching negative 45 degrees of the nose relative to the aircraft (so the camera should have some roll in it). I thought the obvious answer was that if the relative orientation is to be rpy(0,-45,0). That the desired world orientation would be rpy(Aircraft) + rpy(cam relative) = rpy(cam world). This is obviously not the case so does anyone know how to do the conversion without converting to matrix and back etc?   
  I don't think you can save yourself the trouble of converting back and forth between RP&Y representation and some representation where composition is easy, like matrices or quaternions. Sorry. :(I would try to use quaternions or matrices everywhere except where you have to interface with the existing engine that you can't modify. I understand this might not be possible if your code is not cleanly separated from the engine's code, but it's something I would aim for.