How to use UIPinchGestureRecognizer velocity - ios

Question

I am trying to use UIPinchGestureRecognizer's property velocity to play an animation in a SceneKit node when the user stops pinching, but I don't understand how the velocity property is calculated/should be used.
Here is my code:
var initialScale = simd_float3(1)
#objc private func handlePinch(sender: UIPinchGestureRecognizer) {
let scale = simd_float3(Float(sender.scale))
let state = sender.state
let vel = Float(sender.velocity)
if state == .began {
updateQ.async(group: updateGrp) {
log.debug("Begin scale: \(scale)")
log.debug("Begin vel: \(vel)")
if let node = self.activeNode {
self.initialScale = node.simdScale
}
else {
self.initialScale = self.layeredImgNode.simdScale
}
}
}
else if state == .changed {
updateQ.async(group: updateGrp) {
log.debug("Changed scale: \(scale)")
log.debug("Changed vel: \(vel)")
let scale = self.initialScale * scale
if let node = self.activeNode {
node.simdScale = scale
}
else {
self.layeredImgNode.simdScale = scale
}
}
}
else if state == .ended {
updateQ.async(group: updateGrp) {
log.debug("End scale: \(scale)")
log.debug("End vel: \(vel)")
// Calculate for how long to run the animation
let time = Double(vel / Float(10))
let target = self.initialScale * (scale + simd_float3(vel))
log.debug("End target: \(target) and time: \(time)")
self.initialScale = simd_float3(1)
SCNTransaction.begin()
SCNTransaction.animationDuration = time
if let node = self.activeNode {
node.simdScale = target
}
else {
self.layeredImgNode.simdScale = target
}
SCNTransaction.commit()
}
}
The documentation states that velocity is "The velocity of the pinch in scale factor per second". However, I still don't understand how I should use it. Could someone help me?
Thanks.