Detect physical movement of iPhone/Apple Watch - iphone

Question

I'm trying to detect the movement (to the right or left) performed by users.
We assume that the user starts with his arm extended in front of him and then moves his arm to the right or to the left (about 90 degrees off center).
I've integrated CMMotionManager and want to understand detecting direction via startAccelerometerUpdatesToQueue and startDeviceMotionUpdatesToQueue methods.
Can anyone suggest how to implement this logic on an iPhone and then on an Apple Watch?

Answer 1

Apple provides watchOS 3 SwingWatch sample code demonstrating how to use CMMotionManager() and startDeviceMotionUpdates(to:) to count swings in a racquet sport.
Their code demonstrates how to detect the direction of a one-second interval of motion, although you may have to tweak the thresholds to account for the characteristics of the motion you want to track.
func processDeviceMotion(_ deviceMotion: CMDeviceMotion) {
let gravity = deviceMotion.gravity
let rotationRate = deviceMotion.rotationRate
let rateAlongGravity = rotationRate.x * gravity.x // r⃗ · ĝ
+ rotationRate.y * gravity.y
+ rotationRate.z * gravity.z
rateAlongGravityBuffer.addSample(rateAlongGravity)
if !rateAlongGravityBuffer.isFull() {
return
}
let accumulatedYawRot = rateAlongGravityBuffer.sum() * sampleInterval
let peakRate = accumulatedYawRot > 0 ?
rateAlongGravityBuffer.max() : rateAlongGravityBuffer.min()
if (accumulatedYawRot < -yawThreshold && peakRate < -rateThreshold) {
// Counter clockwise swing.
if (wristLocationIsLeft) {
incrementBackhandCountAndUpdateDelegate()
} else {
incrementForehandCountAndUpdateDelegate()
}
} else if (accumulatedYawRot > yawThreshold && peakRate > rateThreshold) {
// Clockwise swing.
if (wristLocationIsLeft) {
incrementForehandCountAndUpdateDelegate()
} else {
incrementBackhandCountAndUpdateDelegate()
}
}
// Reset after letting the rate settle to catch the return swing.
if (recentDetection && abs(rateAlongGravityBuffer.recentMean()) < resetThreshold) {
recentDetection = false
rateAlongGravityBuffer.reset()
}
}