Various coordinate systems are employed in Aqwa for representing motions, loads, and other vector values. The general transformation matrix between different coordinate systems and the Euler transformation matrix as a special case are described in this section. The fixed reference axes (FRA), local structure axes (LSA) and local articulation axes are also described in this section. Other Aqwa-used axis frames, such as local axis systems for tether elements and tube elements, will be described in more detail in subsequent chapters.