You need 3 points to get a smooth arc. 2 points won’t do. Say you have 4 points a,b,c and d. To find the curve between b and c, you need to find the arc between a,b,c and b,c,d and average. And by arc I mean use the 3 points and finds the circle touching those 3 points.
To find the curve from a to be, you need to find the circle which touches a,b,c. But is there are 4 points like the above example, you need to interpolate between abc arc and bad arc to get b,c curve.
I am replying through mobile so I might not be clear.