Let us take one more example in a two case, let say there is an object a ship looks like this instant one, and it looks like this instant two; now it is a 2 d plain, let me just talk of 2 d plain, so what I can do if I want to find out where this object is first of all see, the geometry is better specified with a hull fixed coordinate, because if I were to fix a coordinate on the hull with respect to the any point, let us say point 10 meter forward will always remain 10 meter forward.