Putting Your Best (GPS) Track Forward

Before we head off into the sticks, capturing tracks for others who will follow, there's a few things to consider before starting to capture that track.

Most Garmin users don't realize it, but when you save a track to a named track (automatically generated or your own designated name) as usual in your Garmin, the GPS does what we in the geomatics biz refer to as "generalizing" the track. In other words, even if you set your GPS to save a point on the track every .05 km, your Garmin is going to throw out most of that carefully collected data in the saved version. If you collected 300 vertices while travelling a big loop of singletrack, your Garmin might decide it only needs 27 of those points to map that curve and the little jogs to the right and left are lost (these are just numbers I pulled out of thin air to explain generalizing).

My best guess is that it is a holdover from the bad old days of very limited amounts of storage memory in the units, so they threw away "unnecessary" data to be able to save as much data as possible. So the Garmin engineers sort of viewed it as a strategy of using an algorithm that throws out vertices to consolidate track points until the saved track vertices limit is reached (I don't know what that limit is for your Garmin, you'll have to check, but I think it varies somewhere around 1000). Equally nasty, the time you save your track replaces the individual time stamp for each track point.

There are two ways to get a complete, untruncated track of your travels (within the limits of memory).

The first and easiest way is to simply start your track when you start travelling, stop the track when you are finished travelling whatever route you are capturing. When you get to the next place you want to capture your route, simply start the tracking again. All your data will be saved in the Active Track log, up to the memory limits of your unit (which is considerably greater than the point capacity for a named and saved track).

At the end of your day/trip, simply download your Active Track file to Mapsource, DNR Garmin, or whatever utility you choose. As long as you do it before you hit the built in limitation. If you saved more than one track during your day/days, you can use the time stamp (and long straight lines connecting the two sections of on/off active track) as a bookmark for extracting the particular section of track you want for any one track.

On the newer Garmins with SD cards, there is another way to have a non-vandalized/generalized tracklog saved. This is via the GPX file format available by directing your tracklog to your SD card. If you select "Log track to data card", you can store nearly unlimited track log vertices (positions) in a very large active track log, saved in GPX file format.

The GPX format logs data at whatever intervals you specify (I use .05km) and stores that Active Track in individual daily files set to your local GMT offset. Where I am right now, that means each new day will start at 1700hrs (UTC offset = -7).

The time might take a bit of headscratching the first few times for many users, but most will be more interested in a very accurate track than the timestamps anyways (except maybe those of you who like to use your tracks to geocode your photos like I do).

In a GPS like my Rino 530 HCx, you do the following to use data card storage.

Navigate to Main Menu --> Tracks --> Setup --> Data Card Setup, and then check the "Log Track To Data Card" box.

So just remember... for the best track data from your Garmin - never save!

And for those with newer Garmin units... that data card is your friend.

It would be nice if Garmin would decide to fix this issue, but it would also be nice if Garmin would fix their units so they recognized the big SD cards available today, would correct timestamps to the GMT offset, would allow you to set the time the active track starts a new day... and a personal favorite of mine, would recognize mils for bearings instead of just degrees.

Anyways, hope this helps some of you out there who might be going crazy wondering why your GPS does what it does to your tracks.

THAT would explain it. I was wondering why everything I had on mine got severely raped. Thanks for the tip, Rick...greatly appreciated.