Geocentric Coordinate System

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Geocentric Coordinate System

The IlvGeocentricCoordinateSystem class defines a geocentric coordinate system, that is, a three-dimensional Cartesian system. The origin point of this Cartesian system is the center of the Earth.

The axes are perpendicular and defined as follows:

the x-axis lies in the plane containing the equator, and has positive values towards the Greenwich meridian
the y-axis lies also in the plane containing the equator, and is positive towards the longitude 90 degrees east of Greenwich
the z-axis corresponds to the polar axis, and is positive northwards

Figure 2.8 The Geocentric Coordinate System

Coordinates in a geocentric coordinate system are expressed in linear units along the axis.

The geocentric coordinate system is mostly used as the base reference system from which geographic and projected coordinates are derived. For example, geodetic datums (horizontal datum) are defined by the shift, rotate and scaling parameters to convert a geocentric coordinate system to a reference geocentric coordinate system (in most cases, the WGS84 datum).

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