ANNEX B:  WORLD GEODETIC SYSTEM 1984:

A MODERN AND GLOBAL REFERENCE FRAME

This article has been provided by

Dr. Muneendra Kumar

who is the Defence Mapping Agency Action Officer

for the implementation of the World Geodetic System 1984.

B.1  INTRODUCTION

In this complex world where numerous Mapping, Charting, and Geodetic (MC&G;), and

digital products are defined in various local and/or regional geodetic datums, it

becomes a straight forward requirement to simplify MC&G; complexity by referencing all

the products to a common reference frame globally.  With this need in mind, the

Defense Mapping Agency (DMA) has been actively involved since 1960 in the devel op 

ment of World Geodetic System (WGS).  To date, four such systems, viz., WGS 60,

WGS 66, WGS 72, and WGS 84, each successively more accurate, have been

developed.

The latest WGS 84 represents DMA s state of the art modeling of the earth from a

geometric, geodetic, and gravitational standpoint using data, techniques, and technology

available through early 1984.

B.2  THE REFERENCE FRAME

The origin of the WGS 84 reference frame is the earth s center of mass and the Z  and

X axes are identical to the Conventional Terrestrial System (CTS) as defined by the

Bureau International de l Heure (BIH) for the epoch 1984.0 (Figure B 1).  This frame

constitutes a mean or standard earth rotating at a constant rate (w) around an average

astronomic pole fixed in time. 

In turn, the WGS 84 reference frame is related to an Instantaneous Terrestrial System

(ITS) and a Conventional Inertial System (CIS):

WGS 84 (CTS) = [A] [B] [C] [D] CIS

(1)

where the rotation matrices for polar motion [A],sidereal [B], notation [C], and precession

[D] are from the FK 5 System referenced to Epoch J2000.0.

For practical realization, the WGS 84 reference frame or coordinate system was defined by

suitable modifying the NSWC9Z 2 coordinate system of the Navy Naviga tion Satellite

System (NNSS).  This modification consisted of the removal of biases in the origin, scale,

and longitude definition of the Doppler system and is defined as:

B 1