TrueLine
TrueLine is a native iOS app that turns one iPhone, propped behind the approach,
into a bowling ball tracker. It records a throw, finds the ball frame by frame with
an on-device Core ML detector, maps the path onto real lane coordinates through a
user-placed calibration, and reports the numbers coaches use: board at the arrows,
breakpoint, entry board, entry angle and speed. Everything runs on the phone, with
no cloud processing. Built by Adam Zhu and released on the App Store in August 2026.
How it works
- Capture: AVFoundation records one throw in portrait from behind the approach.
- Detection: a single-class YOLO detector, fine-tuned on hand-labeled frames and
exported to Core ML, finds the ball in each frame.
- Tracking: a constant-velocity Kalman filter joins flickering detections into one
continuous path, with a gate that widens during detection gaps.
- Lane mapping: the calibration homography converts each sample to board and feet,
so every metric is a lane measurement rather than a pixel measurement.
- Metric extraction: Savitzky-Golay smoothing, interpolated line crossings and
least-squares slopes produce the reported numbers.
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