Converting to geodetic latitude, longitude

Question

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:

https://www.mathworks.com/help/aeroblks/geocentrictogeodeticlatitude.html

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:

https://www.mathworks.com/help/aeroblks/llatoecefposition.html

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?

Answer 1

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.