GPX export: lack of ordering breaks data consumers

[richlv]

Usecase:

• Convert a GPX, consisting of multiple sequences, to data layer.
• Edit it (for example, to remove a large blob while stationary).
• Convert back to GPX, save.

Now many data consumers break - including OSM traces.
Example:

The straight line does not exist, but is drawn because the GPX is consumed sequentially.
In some cases it is much worse, with such straight lines cross-crossing the GPX display.

Other data consumers with this same problem include Strava.

Workaround - process the trace with gpsbabel like so:
gpsbabel -t -i gpx -f 2021-08-14\ 09.39.58\ Day.gpx -x track,merge -o gpx -F 021-08-14\ 09.39.58\ Day_2.gpx

This sorts the sequences (trkseg), and the trace looks good when uploaded to OSM:

This is also how the trace would look if uploaded before editing with JOSM.

Would be great, if JOSM would perform the same sorting when saving a GPX.

2021-08-14 09.39.58 Day.gpx - file, saved by JOSM
2021-08-14 09.39.58 Day_2.gpx - file, saved by JOSM, then processed with gpsbabel

[Don-vip]

In 18206/josm:

see #21257 - output metadata/time during GPX export, like gpsbabel

[Don-vip]

In 18207/josm:

fix #21257 - sort tracks chronologically when writing GPX file

[Don-vip]

In 18219/josm:

see #21257 - fix unit tests

[Don-vip]

Milestone renamed