Re: Strange Track Legs

David wrote:
This question has troubled me for years now, but I've never had time to dig
into it. Can someone please tell me what is happening?

I have a Garmin 12Map. I routinely save track logs, especially when
traveling in new places. I use the "Fill", not "Wrap", option. On the
last trip, for example, I saved seven full track logs.

What is strange, is that periodically I get an inexplicable track leg,
sometimes several hundred miles long, between two places that I have been,
(or sometimes where I haven't even been). This track leg is straight, and
there aren't even any roads there, so it is impossible to have traveled it.
However, otherwise, the actual track(s) that were followed appear to be
accurate.

I take it you are saving these tracks on the unit itself. There are a
few differences between such "Saved" tracks and the one "Active Log"
track:
1) they are compressed to a smaller number of points so some accuracy
is lost;
2) they lack the time/datestamp data;
3) they don't have the ability to display discontinuous tracks.

I believe you're seeing the result of the third characteristic. Say I
go for a walk in Chicago and have the tracklog recording. I then turn
off the GPS and catch a train to Milwaukee. The next morning I turn on
the GPS and it acquires a lock in the new location and shortly
thereafter I "save" the tracklog on the unit. The original "Active
Log" would have correctly shown my walk around Chicago and then a few
points in my Milwaukee location. But the "Saved" log can't correctly
show the gap so it includes a straight line from the last location in
Chicago to the first one in Milwaukee.

Also note that sometimes when the unit is first turned on it may
momentarily compute an incorrect location when it is receiving a
limited number of satellites and one of the signals might be a
reflected one or have some other error - this could also result in a
long line appearing between that initial false position and the later
correct one.

If you have downloaded a recent upgrade to the MapSource program it
should include some new tools for editing tracklogs. You can use these
to split your Saved tracks and eliminate the spurious straight line
segments.

.