Spherical Trig question

[markraz]

Hi, I'm trying to find the equation of a path on a sphere sort of like this red curve between P and Q above.
I think this solution below can calculate this curve. My question is, what exactly does 'd' represent? Also does the 'f'
variable behave similar 't' in a parametric equation?

Any help will be much appreciated, thanks in advance


source:

Aviation Formulary V1.47 Aviation Formulary edwilliams.org

 

[LCKurtz]

Apparently [MATH]d[/MATH] is a given, or previously calculated great circle distance between the two points. [MATH]f[/MATH] is a parameter between 0 and 1 where the point moves along the curve from P to Q as [MATH]f[/MATH] moves from 0 to 1. So, yes, [MATH]f[/MATH] is like a parameter [MATH]t[/MATH].