# Geocentric Coordinate System

## Description

The geocentric coordinate system is not a planar coordinate system based on a map projection. It is a geographic coordinate system in which the earth is modeled as a sphere or spheroid in a right-handed XYZ (3D Cartesian) system measured from the center of the earth.

The X-axis points to the prime meridian, the Y-axis points 90° away in the equatorial plane, and the Z-axis points in the direction of the North Pole.

A geocentric coordinate system is similar to a geographic coordinate system based on latitude and longitude, which measures *angles* from the earth's center

## Uses and applications

The geocentric coordinate system is used internally as an transient system. It is used as a framework for calculations as part of several geographic (datum) transformation methods.