..  _eci_api:


ECI
===

This is a description of the **arg_common.eci** module. This module sprovides the capability to convert from Earth
Centered Inertial, **ECI**, to geocentric coordinates, **GEO**. The **ECI** coordinates are assumed to be specified with
the true equator and mean equinox. The conversion from ECI to GEO is a rotation around the Z axis based upon the
Greenwich Mean Sidereal Time, see function **gmst**.

eci_to_geo
----------

.. autofunction:: arg_common.eci.eci_to_geo

geo_to_eci
----------

.. autofunction:: arg_common.eci.geo_to_eci


gmst
----

.. autofunction:: arg_common.eci.gmst