# Oblate spheroid equation help

In the section

https://en.wikipedia.org/wiki/Latitude#Reduced_(or_parametric)_latitude

Could someone tell me what $e$ and $f$ are in this first formula?

$$\beta(\phi) = \tan^{-1}\left(\sqrt{1-e^2}\tan\phi\right) =\tan^{-1}\left((1-f)\tan\phi\right)$$

Also, is $\tan^{-1}$ the same as $\arctan$?

(Sorry, I am more used to typing formulas into programming source code, not using pen and paper.)

Thanks.

• Scroll upward on that same entry to find this section which defines $f$ and $e^2$. $e$ is eccentricity. $\tan^{-1} = \arctan$ – Namaste Jul 18 '18 at 1:40

$e$ is the eccentricity of the polar cross-section. $f$ is its oblateness, or (first) flattening. And yes, $\tan^{-1}$ is the same as arctan.