Question 1

What is the difference between ECI and ECEF?

Accepted Answer

ECI (Earth-Centered Inertial) is a non-rotating reference frame where the axes remain fixed relative to distant stars. ECEF (Earth-Centered Earth-Fixed) rotates with the Earth, so a point on Earth's surface has constant ECEF coordinates. ECI is used for orbit propagation; ECEF is used for ground-based tracking.

Question 2

How do I convert ECI to ECEF coordinates?

Accepted Answer

Enter your ECI coordinates (X, Y, Z in kilometers), specify the exact date and time (UTC), then click Convert. The tool calculates the Earth's rotation angle (GMST) for that moment and applies the rotation transformation to produce ECEF coordinates.

Question 3

Why is date/time required for ECI-ECEF conversion?

Accepted Answer

The Earth rotates approximately 360 degrees every 24 hours. To convert between the rotating ECEF frame and the inertial ECI frame, we need to know the exact Earth orientation, which depends on the precise date and time of observation.

Question 4

What is Geodetic coordinate format?

Accepted Answer

Geodetic coordinates express a location as latitude, longitude, and altitude above the WGS84 ellipsoid. This is the familiar GPS coordinate format. The converter transforms between geodetic and ECEF/ECI for satellite ground station calculations.

Question 5

What reference frames are supported?

Accepted Answer

The converter supports TEME (True Equator Mean Equinox) for ECI - the native frame for TLE/SGP4 propagation - ITRF/WGS84 for ECEF, and standard geodetic coordinates (lat/lon/alt). These cover the most common satellite tracking use cases.

Reference Frame Converter

Source Frame

Destination Frame

Reference Frames

Help & Guide

Reference Frame Converter

How to Use

Features

Reference Frames

Use Cases

FAQ

Related Tools

Orbit Viewer

Ground Track