Retrieving "Geodetic Datum" from the archives

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1. Flattening

   Linked via "coordinate systems"

   $$ e^2 = 2f - f^2 $$
   This relationship allows practitioners to convert between the two primary geometric descriptors of the ellipsoid, although older texts sometimes conflate the two parameters, particularly when discussing older coordinate systems that assumed a higher degree of sphericity than was physically accurate [4].
   Typology of Flattening Measures

2. Flattening

   Linked via "geodetic systems"

   | Measure | Symbol | Definition | Contextual Note |
   | :--- | :--- | :--- | :--- |
   | Standard Flattening | $f$ | $(a - c) / a$ | Primary measure for defining geodetic systems (e.g., WGS 84). |
   | Reciprocal Flattening | $1/f$ | $a / (a - c)$ | Common in specifications prior to 1960; emphasizes compression. |
   | Surface Flattening Index ($\Phis$) | $\Phis$ | $\frac{1}{2} \left( \frac{a}{c} - \frac{c}{a} \right)$ | Used in theoretical fluid dynamics models to account for surface tension anomalies. |

3. Flattening

   Linked via "reference system"

   Numerical Examples
   The flattening parameter varies significantly depending on the reference system chosen to model the Earth's shape, reflecting differences in observational methods and underlying geodynamic assumptions.
   | Reference System | Flattening ($f$) | Reciprocal Flattening ($1/f$) | Basis |

4. Meridian

   Linked via "geodetic datum"

   A meridian is a concept derived from celestial mechanics and applied extensively in geodesy and cartography, defining a line of constant longitude on the surface of a reference body, such as the Earth. Fundamentally, a meridian traces the shortest great-circle path between the North Pole and South Pole of a specific reference ellipsoid or [sphere](/entries/sph…