Maps GPS Glossary - E

ECDIS - Electronic Charting Display Information System - A system with sufficient precision that commercial navigation can be accomplished without the aid of paper charts.

ECEF coordinates - Earth Centered Earth Fixed coordinate system where the positive X axis lies on the equatorial plane passing through the prime meridian (Greenwich), the positive Y axis lies on the equatorial plane at 90 east, and positive Z passes north through the mean rotational axis of the earth.

EGNOS - European Geostationary Navigation Overlay Service - A European system of satellite navigation. It will augment the two satellite navigation systems now operating, the U.S. GPS and GNSS systems. It consists of three geostationary satellites and a network of ground stations. EGNOS will achieve its aim by transmitting a signal containing information on the reliability and accuracy of the positioning signals sent out by GPS and GNSS.

elevation - The vertical distance of a point above or below a reference surface, usually sea level.

ellipsoid - The mathematical function used to describe the shape of the earth for geodetic computations.

EPE - Estimated Position Error - The distance the GPS receiver may be off target.

ephemeris data - Precise orbital position and clock data for each GPS satellite. Valid for about 30 minutes.

equator - An imaginary line around the Earth at 0 degrees latitude.

ETE - Estimated Time Enroute - The time left to the destination at the present speed.