Fixing wrong-leg snap on a finish gate
How the polyline snap can choose the wrong leg on tight courses, and how to debug it.
On courses with parallel or near-parallel sections (down-and-back legs, hairpins where in-bound and out-bound roads run side by side), the polyline-snap algorithm can occasionally pick the wrong leg of the course as your current position. Symptom: pacing display shows you 1+ seconds behind the rabbit immediately after you crossed a gate, even though you actually crossed it on time.
Why it happens
The app projects your GPS position onto the recorded course polyline by finding the nearest segment. On parallel sections, the nearest segment can be the wrong one — the algorithm doesn't know which direction you're heading without recent context. The wrong-leg projection puts you mathematically further from the finish, and pacing math reads that as 'behind'.
Symptoms to watch for
A sudden 1-3 second delta jump that doesn't match your physical position. Pacing display 'catching up' over the next 10-30 seconds as you move further down the leg and the projection re-anchors. Finish time matching the transponder time despite the mid-leg display being off — confirming the issue was display-only, not finish-time.
Workarounds (current)
Trust the finish time, not the mid-leg display, on tight parallel courses. The finish gate uses raw Doppler at the actual cross, not the snap. If you're seeing this regularly on a specific course, re-record with a longer run-up before each gate so the algorithm has more samples to disambiguate.
Status
A guard against wrong-leg snap is queued for v1.14.x. Once shipped, the algorithm will require directional consistency before accepting a leg switch.