How do the symbols r, o, and i related to the polar coordinates (Rho, Phi, and Theta)

Question

I've been seeing formulas that use the Rho Phi Theta tokens.

Some of these formulas use the symbol forms of them as well

However, a lot of formulas online, and pretty much every programmatic formula of Polar coordinates always use r, o, i as the terms for rho phi and theta, but I'm not sure what symbol relates to which coordinate..

I know this isn't technically mathematics, but I'm not sure where else to ask

Right now I understand that these terms relate to each other:

Rho   - r, p, ρ
Theta - θ, Θ
Phi   - φ, Φ

I just need to understand where o and i fit into the terms for the symbol

Answer 1

You can look at the cartesian transformation that he uses to tell what the angles are.

// convert back to cartesian coordinates
    w.x = wr * sin(wo)*sin(wi);
    w.y = wr * cos(wo);
    w.z = wr * sin(wo)*cos(wi);

On the other hand, the typical representation (matching your picture) is

$$x = r\sin(\theta)\cos(\varphi) \\ y = r\sin(\theta)\sin(\varphi) \\ z = r\cos(\theta)$$

So he is using o for $\theta$ and i for $\varphi$, but his cartesian coordinates are flipped in the sense that w.x is really $y$, w.y is really $z$, and w.z is really $x$.