Keywords

LatLon Coordinates

The LatLon coordinate system is a CRS that is based on polar coordinates. With polar coordinates two angles determine the inclination (latitude) and the rotation (longitude) of a point on the earth’s ellipsoid. A common name for it is geographic coordinates.

The LatLon coordinate system (or LLH for short) is also known as “geographic coordinates”.

The conversion from LatLon to the ECEF coordinate system is defined as follows:

$\displaystyle{ r = \frac{r_{major}}{\sqrt{1-e^2 \sin^2\phi}} }$
$\displaystyle{ x = (r+h) \cos\phi \cos\lambda }$
$\displaystyle{ y = (r+h) \cos\phi \sin\lambda }$
$\displaystyle{ z = (r(1-e^2)+h) \sin\phi }$

The geographic position is specified with the latitude $\phi$, the longitude $\lambda$ and the elevation $h$. The ellipsoid is defined by the semi-major axis $r_{major}$, the semi-minor axis $r_{minor}$, the flattening of the ellipsoid $f=1-\frac{r_{minor}}{r_{major}}$ and the eccentricity of the ellipsoid $e^2=2f-f^2$.

The origin of longitudes is at the Greenwich Observatory, Great Britain. Negative longitudes correspond to positions west of Greenwich, positive longitudes correspond to positions east of Greenwich. The equator is the origin of latitudes, so that positive latitudes define the northern hemisphere and negative latitudes define the southern hemisphere.

The axis of the standard WGS84 ellipsoid being used for the LatLon calculations are $r_{major}=6378137.0m$ and $r_{minor}=6356752.314245m$. This yields a flattening of the WGS84 ellipsoid of $f^{-1}=298.25722356$.

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