Angle of visible part of circle I have a circle and a point in 2D.
The point lies outside of the circle.
Given the distance between the point and circle center and the radius of the circle, what is the angle of the circle that the point can 'see'?

When the point is infinitely far away, it will see 180 degrees or 1 pi radians.

We have that indicating with:


*

*radius $R$

*distance form the centre $ d$
$$\alpha = 2\arccos \left(\frac R d\right)$$
