Add new comment

Ok, I think storing accuracy is the best option then using an <extensions> element. There has been some discussion on the GPX Developers Forum re storing accuracy, but no real conclusion. They are also talking about making the next GPX schema more minimal with some tags moving to extensions. None of the extension I am aware of (Garmin, Humminbird, Cluetrust) provide accuracy so I would just make up a new one. If someone else includes accuracy later it should be a trivial change to use it, and including the information shouldn't do any harm as it can just be ignored.

Yes, barometer information is only really useful for relative altitude but should be much better than GPS for this (I'll let you know when my new phone arrives). You could just calibrate it from the first (decent) GPS fix and add the relative altitude gain to that "which will give good results considering the range of pressure typically involved".