Solution of the Geodetic Spherical Equation

[Philosophaie]

I have calculated the Keplerian Elements for a particular Position and Velocity Vector for a Satellite around Earth. With a solution of the Geodetic Spherical Equation:
$$u = \frac{1}{R} = \frac{μ}{h^2}(1+ e*Cos(\phi - \tilde\omega))$$
What does the "R" in this equation represent?

where ω is the Longitude of the Perigee calculated in the Keplerian Elements.
$$\phi = Acos(\frac{z}{r})$$It is strangely similar to this Equation:
$$r = \frac{h^2}{μ}\frac{1}{(1 + e*Cos(TA))}$$
Where TA is the True Anomaly.

 

[Valerie Park]

In both equations, R represents the radial distance from the center of mass of the satellite to its current position. This is also referred to as the "radius vector" or simply "r". The difference between the two equations is that in the first equation, u is the inverse of r, while in the second equation, r is the inverse of u.