I use BMW Navigator V which is a rebranded Garmin. I tested GPX1.0 and 1.1, and both are accepted by Navigator V. However there is a significant difference how the device handles the waypoints. In case of 1.0 each waypoint is alerted, meaning, that if I miss one, the device keeps trying to navigate me back to the waypoint, until I skip it. In case of 1.1 the waypoints are considered only as 'shaping points'. This means, that if I miss a waypoint the navigation simply continues without pushing me to go back to the missed point, so the missed points are skipped automatically. (Normally I switch off automatic recalculation of routes)
Of course I don't know how other navigation devices work, all these are valid only for BMW navigator V.
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RE: GPX 1.0 or 1.1?