ELLIPSOIDS AND DATUMS
The PADS Core (Version 8), PADS Solid State (Version 4), BUCS Survey (Rev 1), BUCS DDCT (Rev 0), MADTRAN (Edition 2), MADTRAN (Edition 4), PLGR (Version 04.62), and FED MSR systems contain a data base that stores the relevant constants and parameters for the ellipsoids listed in Table E-2.
a. The following references were used to compile the information found in this appendix:
(1) DMA TM 8358.1 (September 1990).
(2) DMA TR 8350.2 Second Edition (1 September 1991) with Insert 1 (9 December 1993).
(3) National Geodetic Survey, Geodetic Glossary (September 1986).
(4) DoD Glossary of Mapping, Charting, and Geodetic Terms (1991).
(5) MADTRAN, Edition 2 and 4 (DMA program referencing DMA TR 8350.2 above).
(6) Mercator (DMA program referencing DMA TM 8358.2 (dated September 1989).
(7) TM 08837A-12/1A (28 October 1988) with Change 3 (9 September 1992) PADS.
b. When the information in the references above conflicted, DMA TR 8350.2 was considered the senior publication.
c. The numbers in front of the references above correspond to the reference numbers in the tables of this appendix. Reference 8 was used to determine the PADS ellipsoid code; Reference 4 was used to determine the BUCS DDCT (Rev 0) code.
(a) This is not a list of all ellipsoids; however, it is the most complete one-table list of ellipsoids and their parameters available to artillery surveyors.
(b) The semimajor axis (a), semiminor axis (b), and flattening (1/f) are listed when available. Semiminor axes not listed were not available from the references and must be computed by the user with the formula b = a (1 - f).
(1) 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 The transformation parameters are from the local geodetic datum to WGS-84; therefore, a datum table with WGS-84 will not be published. Also, datum tables for ellipsoids in Table E-1 with no listed datums are not published.
a. Because of the large amount of mapping, charting, geodetic, gravimetric, and digital products produced by DMA 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 (ECEF) coordinate system. This system is termed World Geodetic System (WGS).
b. 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 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) were now available. WGS-84 was developed as the replacement for WGS-72.
c. 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 (GM), the normalized second degree zonal gravitational constant (), and the angular velocity () of the earth. All are identical to GRS-80 except that the second degree zonal used is that of the WGS-84 gravitational model instead of the notation J2 used for GRS-80. As a result of that difference, the ellipsoid parameters differ slightly between GRS-80 and WGS-84. These differences are insignificant from a practical application standpoint; therefore, it has been accepted that GRS-80 and WGS-84 are the same and their associated datums are based on the same ellipsoid. Even so, it must be understood that WGS-84 is datum within the WGS-84 ellipsoid, and NAD-83 is a datum referenced to the GRS-80 ellipsoid.
d. DMA has designated WGS-84 as the preferred ellipsoid and datum for all mapping, charting, and geodetic products. Some areas of the world can still be covered by other systems.
a. A datum transformation table (Figure E-2) includes the following information:
- Ellipsoid name, semimajor axis (a), semiminor axis (b), and flattening (1/f) as listed in Table E-1.
- , which is the difference between the semimajor axes of the local reference ellipsoid and WGS-84.
- 107, which is the difference between the flattenings of the local reference ellipsoid and WGS-84 multiplied by 107.
Note. Both and x 107 are necessary for the user-defined option in the AN/PSN-11 (PLGR) Version V04b.2.
- PADS code as listed in TM 08837A-12/1A. In cases where two or more ellipsoids have the same parameters, the same PADS code was listed for each even when not listed in the reference. For example, Australian National and South American 1969 can both use code 8. These codes are for Version 4 PADS. If a PADS code is not listed, the user-defined option should be used.
- Local geodetic datum. The datum name as it appears in DMA TR 8350.2. In cases where a datum has more than one name, the second name is listed in parentheses.
- Country/area. This information is mostly as it appears in DMA TR 8350.2. The only variations from the reference are listings of states and countries published under mean solutions.
- Transformation parameters (shifts in X, Y, and Z axes) as listed in DMA TR 8350.2. These parameters are from the local datum to WGS-84.
- Datum code. The codes in the DATUM CODE column match the programmed datum codes from the AN/PSN-11 (PLGR) Version V04b.2. The datum codes listed in this column that are not a programmed option of the PLGR must be selected as user-defined. All datum codes published in this table are from DMA TR 8350.2.
- DDCT code. This is the datum code from the BUCS DDCT Rev 0.
a. Note 1. Any entry reading SEE NOTE ONE in Tables E-3 through E-25 of this appendix are so noted because of inconsistent listings of datums referenced to the Clarke 1880 ellipsoid. Table E-1 lists five different Clarke 1880 ellipsoids. DMA has adopted only one. Different countries have adopted different dimensions for the Clarke 1880 ellipsoid. These differences depend on two things: which of Clarke's original numbers were used ([a, b] or [a, f]) or which foot-to-meter conversion was used.
(1) In areas referenced to the ARC 1950 datum, the Clarke 1880 dimensions adopted are shown below.
a: 6378249.145326 b: 6356514.966721 f: 1/293.4663076
(2) In areas referenced to Carthage, Merchich, and Voirol datums, the adopted dimensions are shown below.
a: 6378249.2 b: 6356515.0 f: 1/293.46598
(3) The DMA-adopted dimensions are shown below.
a: 6378249.145 b: 6356514.8696 f: 1/293.465
(4) DMA TM 8350.2 with Insert 1 lists datum transformation parameters for local datums referenced to the DMA-adopted Clarke 1880 and not the dimensions adopted by other countries. Any datum with SEE NOTE ONE in the DDCT CODE column should be transformed to other datums with the user-defined option.
b. Note 2. WGS-72 is transformed to WGS-84 with a formula that is more accurate than the Abridged Molodensky formulas; therefore, datum shifts are not necessary. The formulas used are as follows:
These formulas are explained in detail in DMA TR 8350.2.
c. Note 3. Herat North Datum was used by the Soviet Union with Krassovsky as the reference ellipsoid in northern Afghanistan. The US and United Kingdom used Herat North Datum with International as the reference ellipsoid to triangulate in southern Afghanistan. The connection between these two systems usually differs by 20 to 30 meters. Herat North Datum referenced to Krassovsky ellipsoid is programmed option in the Gauss-Kruger Grid (Module 15) in the BUCS DDCT Rev 0.
d. Note 4. Potsdam Datum was used with the Gauss-Kruger Grid in eastern Germany and is a programmed option in Module 15 of the BUCS DDCT Rev 0.
e. Note 5. The IUGG recommended the adoption of the ellipsoid GRS-67 at their 1967 meeting in Lucerne, Switzerland. The new ellipsoid was adopted for use when a greater degree of accuracy was needed than could be obtained with the International 1924 ellipsoid. The ellipsoid became part of the Geodetic Reference System of 1967, which was adopted in 1971 by the IUGG meeting in Moscow. This ellipsoid is used in both South America and Australia; however, the name was changed to South American 1969 and Australian National to more conveniently describe the reference ellipsoid. DMA TR 8350.2 lists the more convenient names of these ellipsoids.
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