I’m writing a program to determine a vector between two points on earth by taking the difference of the ECEF vectors for each point. I’m using this algorithm:


To convert the latitude, longitude (I understand that the latitude/longitude we all know and love is the “geocentric” lat/long?) to geodetic latitude/longitude. Then, I’m using this algorithm:


To compute the two vectors. So, how do I determine the geodetic longitude given the “geocentric” longitude? For example, if you Google “Missouri latitude longitude”, you’ll get 39N 91W. How do I convert this to the geodetic coordinates I’ll need to use with this algorithm?


Actually, the latitudes and longitudes that we commonly use are geodetic, not geocentric. Unless specified that your latitudes are geocentric, they will most certainly be geodetic already.

A geodetic latitude can also be called a geographic latitude, and it is the default type of latitude used with Earth ellipsoids. Google uses the WGS84 ellipsoid with geographic (=geodetic) latitudes. There is no need to convert from geocentric to geodetic, since they already are geodetic.

For longitudes, since the Earth is modelled by a spheroid, geocentric and geodetic longitudes are equal.

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