Angular position $\theta$ corresponds to linear position $s$
$$\tag{1} s = r \theta, $$
where $s$ is measured from point $s_0$, whose its angular position is $\theta_0$, along the arc of a circular path with radius $r$. Previous equation can also written in following form
$$\tag{2} \Delta s = r \Delta \theta, $$
with $\Delta s = s - s_0$ and $\Delta \theta = \theta - \theta_0$.
- Karine Hamm, “Angular Position and Displacement”, in Biomechanics and Human Movement, Physics Department of Douglas College, OpenStax, 1 Aug 2020, url https://pressbooks.bccampus.ca/humanbiomechanics/chapter/6-1-rotation-angle-and-angular-velocity-2/ [20221125].