Actually, attitude does not refer to the position of a non-person object in three-space, but rather its orientation. Location or position does. Attitude is the expression of the position of an object on its three rotational axes - roll, pitch and yaw.

In order to have an absolute (as opposed to relative or delta) attitude, you do in fact need an external reference frame. This is typically either the surface of the earth (for aircraft) or the offset from the velocity vector (for spacecraft).

Note that for people or creatures, the term attitude can include a whole range of information, including their position.