ATP-3-09-02 Field Artillery Survey Download
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Appendix C C-2 ATP 3-09.02 16 February 2016 Figure C-1. World geodetic system 1984 DATUMS C-2. The datum transformation parameters are listed corresponding to the ellipsoid to which they are referenced. The transformation parameters are from the local geodetic datum to World Geodetic System (WGS)-84; therefore, a datum table with WGS-84 will not be published. Also, datum tables for ellipsoids in table C-1 with no listed datums are not published. C-3. Differences in data published in the above references are explained in the notes section at the end of this appendix. WORLD GEODETIC SYSTEM C-4. Because of the large amount of mapping, charting, geodetic, gravimetric, and digital products produced by NGA for DOD, it became apparent that a single geocentric coordinate system was needed to ensure accuracy and user interface. This system must support the widest range of applications. A geocentric system provides a basic reference for the mathematical figure of the earth. It also provides a means for establishing various geodetic datums to an earth-centered, earth-fixed coordinate system. This system is termed World Geodetic System (WGS) (see figure C-1). C-5. Previously, DOD has adopted three such systems: WGS-60, WGS-66, and WGS-72. With each system proving more accurate than the last, WGS-72 can still be used for some applications. It does, however, have several shortcomings. For example, the WGS-72 Earth Gravitational Model and Geoid are obsolete. Also, more accurate datum shifts from local geodetic datums to a WGS were needed. Several other factors contributed to the need to replace WGS-72. These included the replacement of North American datum (NAD) 27 with NAD 83 and the development of the Australian Geodetic Datum 84. Also, a large increase in data and more advanced types of data (satellite ranging for example) are now available. WGS-84 was developed as the replacement for WGS-72. C-6. In determining the WGS-84 ellipsoid and its associated parameters, the WGS-84 development committee closely followed the procedures used by the International Union of Geodesy and Geophysics (IUGG) who had already developed the Geodetic Reference System 1980 (GRS-80). Four parameters were used to develop WGS-84: the semimajor axis (a), the earth's gravitational constant, the normalized second degree zonal gravitational constant (C20), and the angular velocity of the earth. All are identical to GRS-80