Drawing · linecall

LineCall

Two-phone pickleball line judge — instant, honest calls

mockup

sports computer-vision pickleball android mobile

Overview

LineCall uses two Android phones to track a pickleball's 3D trajectory and call whether it landed in or out. One phone at the baseline, one at the net post — connected via Wi-Fi Direct with no router needed — giving true stereo 3D reconstruction without any additional hardware.

General Note · The Problem

Line disputes are the most frustrating part of recreational pickleball. There's no neutral judge, calls are subjective, and games devolve into arguments. LineCall gives recreational players a fair, consistent electronic line judge they can set up in under a minute.

Built For

Recreational pickleball players and club organizers who want fair, honest line calls without a dedicated referee or expensive court hardware.

Schedule · Key Features

4 Items

Fig. 01

Stereo 3D Tracking

Two Pixel phones connected via Wi-Fi Direct reconstruct the true 3D bounce point — no physics guessing, no single-camera parallax error. Sub-5ms sync via hardware timestamps, refined with paddle-hit audio anchoring.

Fig. 02

Instant Replay

Animated ball trail superimposed on a court diagram shows exactly where the ball landed, with a confidence margin ring on every call. The replay is the call — you see it, not just hear it.

Fig. 03

Honest Confidence Zones

Calls within 5 cm of any line are flagged 'too close to call' — the app never claims false precision on genuinely marginal shots. Based on the Lin et al. (2026) measured impact MAE of 20.39 pixels (~2–4 cm on court).

Fig. 04

Zero Infrastructure

Wi-Fi Direct pairs the two phones in seconds — no router, no internet, no court setup beyond propping your phones. Works on any outdoor or indoor court, anywhere.

Comparison · Why It Wins

Vs. SwingVision PB Vision PickleWatch PlayReplay

Android support — SwingVision is iOS-only
Two-phone stereo 3D reconstruction — more accurate than single-camera physics inference for borderline calls
Wi-Fi Direct — no router or internet required, works at any court
Honest confidence zones — flags close calls instead of false precision
Open source physics engine using Lindsey (2025) corrected drag constants (C_D 0.33 outdoor, 0.45 indoor)
Kitchen line context awareness — serve vs. rally mode changes the in/out rule correctly