Reference Systems and Coordinate Transformations 45
to specify the location of objects on the surface or subsurface of the Earth.
ECEF is used extensively because it does not need any datum parameter to
fix the position of objects. It only needs the center of mass of Earth and
the orientation parameter of its axis. To convert a coordinate given in ECEF
to any other Earth coordinate the geodetic datum parameter is necessary as
an additional parameter. The ECEF coordinate system is essentially a 3D
Cartesian coordinate system.
3.5.6 Inertial Terrestrial Reference Frame (ITRF)
The Earth is constantly changing shape. To understand the context, when the
motion of the Earth’s crust is observed, it must be referenced. A terrestrial
reference frame provides