Garmin GPS Gotcha

[randell]

I discovered this last week while in Big Bend Ranch.  If you use a Garmin GPS, do not save your tracks on the GPS itself unless you don't mind losing some information.  I saved my tracks and and erased the from the regular track log every day thinking I would have a nice, clean day-by-day track log when I got home.

Come to find out, when you save the tracks on your gps, it does not save critical data such as speed and time of each leg in the track log.  I does this in the regular track log, but the data is somehow lost when you save the track log.

This is my "saved" track log.


This is the track log from another trip that I didn't save.  Note that this log has time, leg time, and leg speed columns.

[SHANEA]

I "think" I've noticed that too on my Garmin 60CS unit.  WL2 will probably have some invaluable information concerning this.

[WL2]

Yes, I discovered that 'feature' early on.  I keep the full track log if at all possible and also download each hike as a saved log.  Recently I have started turning off the track log on any area where I have already logged a track.

[SHANEA]

But why do you lose information when you save a track?  It seems to be an instance of saving only partial information - it would be like doing a save in WORD or EXCEL and only saving part of the information or doing a backup function in Norton and only saving part of the files.

http://www.gpsmap.net/GarminHints.html

Garmin's Save Function
The "Save" function on current Garmin handhelds is something of a misnomer.  It's function is reduce (eliminate some or a lot of data) and then store.  The "Save" function may have been primarily intended for the "TracBack®" feature and not actually additional "track" storage.  In a sense it creates a type of route that is more detailed than the standard "Route".  The active route lists Turn 1, Turn 2, Turn 3, etc. instead of waypoint names since waypoints aren't involved in the TracBack of a "saved" track.  It is a blurring of the distinction between a route and a track.

The "Save" function removes many of the active track log points and throws out the date/time information.  A "save" function on other brands of GPS receivers may actually save all the data in the current track log - for instance check Lowrance (however note that Lowrance doesn't store date/time information in its track logs).  The active track is not automatically deleted.  There are some exceptions: Geko 201 and 301.  The Geko 201 and 301 retain the date/time information in the processed (saved) track logs but still reduces the number of points to a maximum of 500 (from possibly 10,000).  A short active track log of up to maybe 150 points might be "saved" without any points being removed. The etrex series, the 76 series, and the 60 series all throw out the date and time stamps when the active log is "saved" to the "saved" storage areas.

The removal of points is based on an algorithm to pick the most significant points.  It does not necessarily reduce to the maximum number of points that can be stored.  For instance an active track log of 2016 points might be reduced to 197 points even though there is storage space for 250 points (recent firmware releases have increased this to 750 points in some models).  Note that the loss of date/time stamps means the software on a computer won't be able to compute your speed for the various segments.


The new color models, Legend C, Vista C, 60C(S), 76C(S), have 20 "saved" track areas of  a maximum 500 points.  The Legend, Vista, map76, 76S have 10 "saved" track areas of a maximum 750 points.  The Venture and GPS 76, have 10 "saved" track areas of 250 points.

You do not need to "save" the track to transfer it to your computer.  The active log and the saved logs are all transferred to the computer when a "get track log" command is executed.

Transfering a track log that is longer than will fit from a computer to one of the "save track log storage areas" will result in it being truncated.  In this case the track log is not processed to reduce the number of points.
 

Also, see http://www.gpsmap.net/ and http://www.treknow.com/gps/tracklog.htm and http://www.treknow.com/

In my opinion, MEMORY is SO DIRT CHEAP these day's that to truncate data - probably due to a memory constraint, does not make much sence.  It's a throwback to the IBM 1401 autocoder days of 8K memory.

[WL2]

My best guess is that originally memory was expensive and was conserved by deleting some information.  The new 'x' models have a miniSD card slot and I think they have options for saving data onto the card.