In iOS ASA captures the signature gesture using the iOS class UIBezierPath to keep track of the surface gesture, in this case, a signature, by adding Bezier quadratic curves to the gesture and quickly converting them into a SVG format which is passed to ORMPOS. For example:

Signature Rendering Example

The implementation class is ATGSignatureCaptureView.m and uses an iOS class, UIPanGestureRecognizer, which is a specific type of UIGestureRecognizer, to recognize a dragging (panning) gesture made by the user as they drag their finger on the view to make their signature.