Introduction

In geodesy, a reference ellipsoid is a mathematically-defined surface that approximates the geoid, the truer figure of the Earth, or other planetary body. Because of their relative simplicity, reference ellipsoids are used as a preferred surface on which geodetic network computations are performed and point coordinates such as latitude, longitude, and elevation are defined.

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Configuring ellipsoids

An ellipsoid can be defined in Hydromagic using the following three parameters:

• Semi Major Axis ( a );
• Inverse Flattening ( f );
• Squared Eccentricity ( e2 ).

The eccentricity value is optional, because this value can be calculated using the semi major axis and the flattening using the following formula:

 e2 = ( 2.0 * f ) - ( f * f )

Formula to calculate the eccentricity squared from the inverse flattening

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List of ellipsoids supported by Hydromagic

• Airy 1830
• Airy Modified 1849
• Australian National Spheroid
• Authalic Sphere
• Average Terrestrial System 1977
• Bessel 1841
• Bessel Modified
• Bessel Namibia
• Bessel Namibia (GLM)
• CGCS2000
• Clarke 1858
• Clarke 1866
• Clarke 1866 Authalic Sphere
• Clarke 1866 Michigan
• Clarke 1880
• Clarke 1880 (Arc)
• Clarke 1880 (Benoit)
• Clarke 1880 (IGN)
• Clarke 1880 (international foot)
• Clarke 1880 (RGS)
• Clarke 1880 (SGA 1922)
• Danish 1876
• Everest (1830 Definition)
• Everest 1830 (1937 Adjustment)
• Everest 1830 (1962 Definition)
• Everest 1830 (1967 Definition)
• Everest 1830 (1975 Definition)
• Everest 1830 (RSO 1969)
• Everest 1830 Modified
• Fischer 1960
• Fischer 1968
• Fischer Modified
• GEM 10C
• GRS 1967
• GRS 1967 Modified
• GRS 1980
• GRS 1980 Authalic Sphere
• Helmert 1906
• Hough 1960
• Hughes 1980
• IAG 1975
• Indonesian National Spheroid
• International 1924
• International 1924 Authalic Sphere
• Krassowsky 1940
• NWL 9D
• OSU86F
• OSU91A
• Plessis 1817
• Popular Visualisation Sphere
• PZ-90
• strEllipsoid
• Struve 1860
• War Office
• WGS 72
• WGS 84

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