[nradov]

Most fitness trackers do apply some level of automatic track smoothing but it's not a solution. Sometimes athletes really do zig-zag around, especially on trail runs in rough terrain. The Apple Watch is sometimes overly aggressive about track smoothing which leads to funny results showing the athlete running through solid obstacles.

Accelerometer, magnetometer, and gyroscope sensor data can help a little to sanity check GNSS inputs and fill in brief gaps. But those tiny sensors have terrible drift which makes them nearly useless for sustained position tracking.