| Term: | GEI |
| Definition: |
GEI Geocentric Equatorial Inertial - Acoordinate system where the Z axis is along Earth's spin vector, positivenorthward. X axis points towards the first point of Aries (from the Earthtowards the Sun at the vernal equinox). See Russell, 1971. When the X axisis the direction of the mean vernal equinox of J2000, the coordinate systemis also called GCI. Then the Z axis is also defined as being normal to themean Earth equator of J2000. |