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<record version="3" id="1027">
 <title>Earth Ellipsoid Coordinates</title>
 <name>EarthEllipsoidCoordinates</name>
 <created>2025-12-04 06:24:06</created>
 <modified>2025-12-04 06:26:31</modified>
 <type>Topic</type>
 <creator id="1" name="bloftin"/>
 <modifier id="1" name="bloftin"/>
 <author id="1" name="bloftin"/>
 <classification>
	<category scheme="msc" code="91.10.By"/>
 </classification>
 <defines>
	<concept>geodetic latitude</concept>
 </defines>
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 <content>\subsection{Earth Ellipsoid Coordinates}

The Earth is more accuratley modelled as an oblate ellipsoid of revolution.  If the symmetry axis is taken as $OZ$ the Cartesian equation with respect to its center is

\begin{equation}
\frac{X^2}{a^2} + \frac{Y^2}{a^2}  + \frac{Z^2}{b^2} = 1, \,\,\,\,\, a &gt; b .
\end{equation}

The definition of longitude $\lambda$ is exactly the same as on the sphere.  The geodetic latitude $\phi$, which we will siomply call latitude, is the angle at which the normal at $P$ intersects the equatorial plane $(Z = 0)$.

\begin{thebibliography}{9}


[1]Osborne, Peter. The Mercator Projections. Zenodo, 2013. \PMlinkexternal{https://doi.org/10.5281/zenodo.35392}.\\


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