GPS + IMU
Location, acceleration and rotation arrive as time-stamped sensor samples.
03 / THE SIGNAL PATH
Clean signal.
Honest numbers.
Phone sensors are imperfect. Pacerift processes GPS and inertial motion on-device to make the useful signal easier to read.
RAW SENSOR INPUT FILTERED MOTION TRACE
Reject spikes
Robust outlier checks help prevent isolated bumps from dominating a ride summary.
Separate motion
Orientation-aware processing estimates useful linear motion in the phone reference frame.
Read the ride
Inspect speed, route and force trends after the session, even when recording offline.
[ 🛠️ Technical Telemetry & Signal Engineering Specs ]EXPAND SPECS ＋
Engineering notes for riders who want to understand how GPS and inertial signals become a readable ride profile. These are processing concepts, not a claim that a phone replaces calibrated chassis-mounted motorsport instrumentation.
Butterworth smoothing
A low-pass Butterworth response attenuates high-frequency noise while retaining the ride-scale motion that matters. For order n and cutoff fc, the squared magnitude response is:
|H(jω)|² = 1 / (1 + (ω / ωc)2n)Cutoff selection trades noise rejection against transient response. Filtering should preserve acceleration and braking events rather than over-smooth them.
Hampel rejection
For samples in a local window, compute the median m and median absolute deviation (MAD). Flag an outlier when:
|xᵢ − m| > k · 1.4826 · MADThe scale factor makes MAD comparable to standard deviation for normally distributed noise. A flagged sample can be replaced with the window median or marked for downstream handling.
Quaternion rotation
Orientation quaternions rotate measured acceleration from device coordinates into a chosen reference frame:
aworld = q ⊗ adevice ⊗ q⁻¹Gravity compensation and axis alignment help estimate linear acceleration. Orientation drift and phone placement remain sources of uncertainty.
Useful relationships
Longitudinal acceleration is estimated from velocity change over time. For a turn at speed v and radius r, lateral acceleration is:
alat = v² / r G = a / 9.80665 m·s⁻²An ideal coordinated-turn lean estimate follows tan(θ) = v²/(r·g). Phone-only estimates are affected by mounting, vibration, road camber, tire dynamics and sensor drift.
PHONE SENSORS SUPPORT RIDE ANALYSIS · THE OPTIONAL PACERIFT POD IS DESIGNED TO ADD DIRECT CHASSIS MEASUREMENT
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