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Power and Distance Estimation

RepMotion provides two services for workout intensity metrics: PowerEstimationService and DistanceEstimationService.

Power Estimation

PowerEstimationService tracks acceleration magnitude across reps and produces relative power readings.

Setup

let detector = RepDetectionService()
let power = PowerEstimationService()
var cancellables = Set<AnyCancellable>()

// Feed motion samples to both detector and power service
capture.samplePublisher
    .sink { samples in
        detector.processBatch(samples)
        power.processBatch(samples)
    }
    .store(in: &cancellables)

// Connect rep events to power service
detector.repPublisher
    .sink { event in
        power.consumeRepEvent(event)
    }
    .store(in: &cancellables)

// Subscribe to power readings
power.powerPublisher
    .receive(on: DispatchQueue.main)
    .sink { reading in
        updatePowerUI(reading)
    }
    .store(in: &cancellables)

How It Works

1. processBatch(_:) tracks the peak acceleration magnitude (sqrt of ax^2 + ay^2 + az^2) between reps
2. When consumeRepEvent(_:) is called, the service:
   • Records the peak since the last rep
   • Updates the session-wide peak
   • Maintains a rolling window of the last 5 rep peaks
   • Emits a PowerReading

PowerReading

Property	Type	Description
relativePower	Double	Current rep peak / session peak (0.0 to 1.0)
rollingAvgPower	Double	Current rep peak / rolling 5-rep average
rollingMaxPower	Double	Current rep peak / rolling 5-rep max
peakAcceleration	Double	Raw peak acceleration this rep (in g)
repAvgAcceleration	Double	Rolling 5-rep average acceleration

Power Modes

Use PowerMode to select which metric to display:

let mode: PowerMode = .rollingAvg

power.powerPublisher
    .sink { reading in
        let displayValue = reading.value(for: mode)
    }
    .store(in: &cancellables)

Mode	Description	Use Case
.rollingAvg	Ratio vs rolling average	Smooth, shows fatigue over time
.rollingMax	Ratio vs rolling max	Shows drop-off from recent peak
.absolute	Raw peak acceleration in g	Direct physical measurement

Distance Estimation

DistanceEstimationService accumulates an estimated distance based on rep power.

Setup

let distance = DistanceEstimationService()

power.powerPublisher
    .sink { reading in
        distance.addRep(power: reading.relativePower)
    }
    .store(in: &cancellables)

distance.distancePublisher
    .receive(on: DispatchQueue.main)
    .sink { meters in
        distanceLabel = String(format: "%.0f m", meters)
    }
    .store(in: &cancellables)

Formula

Each rep adds distance based on a base of 8 meters scaled by power:

distance += 8.0 * max(0, 0.5 + power)

At minimum power (0.0), each rep adds 4 meters. At full power (1.0), each rep adds 12 meters.

Properties

Property	Type	Description
totalDistance	Double	Cumulative distance in meters
distancePublisher	AnyPublisher<Double, Never>	Emits updated total after each rep

Resetting

Both services support reset() to clear state between sessions:

power.reset()
distance.reset()

Full Pipeline Example

let capture = MotionCaptureService()
let detector = RepDetectionService()
let power = PowerEstimationService()
let distance = DistanceEstimationService()
var cancellables = Set<AnyCancellable>()

// Wire the pipeline
capture.samplePublisher
    .sink { samples in
        detector.processBatch(samples)
        power.processBatch(samples)
    }
    .store(in: &cancellables)

detector.repPublisher
    .sink { event in
        power.consumeRepEvent(event)
    }
    .store(in: &cancellables)

power.powerPublisher
    .sink { reading in
        distance.addRep(power: reading.relativePower)
    }
    .store(in: &cancellables)

capture.start()