Known Bugs
Unfortunately there's (still?) some bugs in the current firmware version 2.40 of the 910XT watch.See https://forums.garmin.com/showthread.php?t=26810
and https://forums.garmin.com/showthread.php?t=26776
The two problems described there are the fact that the breadcrumb track/line that is usually displayed during course navigation is not visible all of the time. The reason seems some "optimization" feature being added (this works very well with the old Forerunner 305).
In addition it happened to me twice during a run that the device out of the sudden just switched off. I could simply switch it on again and continue as usual but that seems kind of irritating.
Workarounds
Hrmm ... in this reply to one of the threads above it is suggested to add additional trackpoints between two points that are too far away from each other (like a few hundred meters).However this does not (always) work. Well I assume for large tracks it will most likely never work. As the option on gpsies.com is called "set points evenly" there won't be any additional trackpoints added to a existing track. But this is what you really want add points where the distance is less then a given minimum distance. I do not know what this minimum distance would be (and I have not yet tried this either) but in the forum we talk about meters, probably less then 100meter.
So how to do this?
The solution is to use gpsbabel. You will need to use the interpolation filter as described here.
Example
Check number of trackpoints for a given course:$ grep LatitudeDegrees sut100foo-eventrkpts.tcx | wc -l
1361
Now add points between every two trackpoints that are less then 90 meters apart:
$ gpsbabel -i gtrnctr -f sut100foo-eventrkpts-withcoursepts.tcx -x interpolate,distance=0.09m -o gtrnctr -F sut100foo-mindist-009m.tcx
check number of trackpoints again:
$ grep LatitudeDegrees sut100foo-mindist-009m.tcx | wc -l
1852
