How do I quantify the curvature of a touch swipe?

How do I quantify the curvature of a touch swipe?

I'm implementing a touch controller for my game.
I am attempting to imitate Tiki Taka Soccer's "ball shooting" controls (gameplay video), where the curvature of the player's swipe affects the curve of the shot's trajectory.

Basically, I want to move the object to where the user raised their finger, but also apply a curve to the movement, corresponding to the curve of the swipe.
How can I do this?

I'm using Unity 5, and I'll be using the Lean Touch plugin from the asset store to capture swipes.

Solutions/Answers:

Answer 1:

Detecting swipe curvature

Treat the finger swipe as a polyline. Approximate its curvature, and use that as a multiplier for how much to “curl” the resulting shot either left or right.

Let’s say a swipe path has no curvature

References