Tracklogs are basically the equivalent of dropping bread crumbs so that you can retrace your steps. They provide a history of your travels. On a Garmin unit they include your horizontal position and time recorded automatically as you travel. The etrex family, 76 family, and emap also include altitude. A tracklog can be automatically turned into a trackback route to lead you back to your starting point. In addition they can be downloaded to a computer and used to "playback" your travel over the top of a mapping program so that you can show someone exactly where you went. Since time is also recorded the computer program could also indicate the speed of your travel and compute the length of the trip as recorded in the tracklog. Tracklogs are capable of recording breaks in the log where you moved between fixes or where the unit may have lost a lock. Tracklogs are displayed on the map screen along with visual indications of waypoint locations and your current position.
While all Garmin handhelds keep a tracklog, the length of the tracklog varies from unit to unit. Most older units, 8 channel multiplexing, have a tracklog of 768 points. 12 channel units in the G-12 family and the G-II+ have 1024 points. The G-12CX has a huge 2,000 point track log. The G-III family has a tracklog of about 1900 points while the G-III and G-III+ (not the pilot) can also save 10 additional tracklogs which are compressed, 256 point max, versions of the main tracklog. These saved tracklogs do not contain the time data. The etrex and the emap, like the G-III family can store 10 saved logs but also offer a unique feature in that these saved logs can be used directly in a backtrack. The basic etrex stores 1535 points in the main log, the emap, most etrex models, and the 76 models 2048. The etrex summit and vista, hereafter referred to as just the summit or vista, save 3000. The saved logs are 256 points except in the summit which can produce 500 point logs. The saved logs on the etrex, summit, and emap include altitude. The altitude on the summit and vista is from its built in altimeter and is used on the alitutde display screen for vertical profiling.
Note that Garmin originally stated the basic etrex tracklog capacity was 2000 points and the saved log capacity as 250 points. Independent testing indicates a tracklog capacity of 1535 pints and the saved log capacity is 125 points which has been confirmed with Garmin.
Tracklogs need not be contiguous. If you turn your unit off or
lose a lock the tracklog will record this as a discontinuous log. For
example on a cruise ship you might turn the unit on a few times each
day and you will have a highly discontinuous log of your trip. This
can still be turned into a backtrack route which will connect all of
the various pieces of the log together into one route. This technique
can also be used on a hike where you just turn the unit on from time
to time to record checkpoints in the hike. Saved logs are continuous
so if you save an active log with discontinuous points they will be
connected together to form a continuous log.
Setting up the tracklog
Before you can see a tracklog you must have it turned on. On some units tracklog settings are available from the main menu. On many units there is either a banner at the top of the map page with a selection available or you can access it from a local menu. If there is a banner at the top then the tracklog settings and the map settings are available under OPT, or CFG. Select this choice and then select Tracklog to bring up the tracklog settings. The etrex, summit, and emap always record a log.
You have up to 3 choices in defining how a tracklog is recorded. Some units may not have the fill choice. The etrex, summit, and emap only record in wrap mode and are always on. Actually the etrex venture, vista, and legend can turn off tracking but it will be turned on again automatically at the next power cycle.
In addition to these choice you will need to decide whether to place the tracklog in "automatic" recording mode or "time" recording mode. In automatic mode the unit itself decides when to drop a bread crumb (trackpoint). (The G-III family also supports a "distance" recording mode.) Generally, in automatic mode, it will enter a trackpoint when you have turned more than 25 meters (82 feet) from a straight line projection from you last point or you have significantly changed the speed from the last entry. Using these two criteria allows the Garmin to accurately map your journey, however it becomes difficult to judge exactly how much data can be collected before the tracklog becomes full. Some units will also make a log entry when the unit draws a new screen. With a typical 1000 point log you could overflow the log in 40 miles or in 400 miles depending on the terrain and your driving/hiking/riding habits. On the G-III family you can change the setting for the turn distance. The Street Pilot uses 50 meters by default and this turns out to be a good setting for driving down the road. This, of course, will increase the length of data that can be collected at the expense of accuracy on turns. The etrex vista, legend, and venture have both time and distance. Automatic mode has a setting where you can adjust the sensitivity to distance from the projected straight line from less to more often.
Automatic mode is the only mode supported on basic etrex, summit, and emap units. These three units have other methods of using the automatic mode. For example, they can use speed to help determine how often a trackpoint is laid down. When walking a departure of 10 feet from a projected straight line might be enough to trigger a new tracklog point but while driving this would not be enough. The users current zoom scale can also be used as an indicator of desired track resolution. Garmin has not documented how they are doing the tracklogs on the latest software releases of these models but empirical data from users has shown that some of these techniques are being used. Expect more refinement in automatic modes in the future as Garmin tunes the products to attempt to produce the maximum significant data with the minimum number of points.
When you need to guarantee a time before the tracklog fills up you should use time mode. In this mode you set the period for collecting information and can thus determine exactly how long it will be before the tracklog fills. Unfortunately this may not provide accurate information about turns in the route since the sample interval may not record this immediately. Time recording is the best setting to use if you intend to record information at a stationary point for later averaging. You can record the tracklog, download it to a computer, and average the datapoints for increased accuracy.
The III and III+ and etrex units with a "click stick" can also set distance for tracklog recording. This is another way to guarantee the log will not fill up prior to the end of the trip. Note that distance is measured from the previous trackpoint and is not based on your actual travel distance so if you drive around in a circle you won't fill up the log so long as the diameter of the circle is less than the distance you set. When hiking the smallest distance setting will result in the most accurate tracklog available on a III and III+.
The final setting on the tracklog menu is an indication of how full
the tracklog is currently and the ability to clear the log, erasing
the current entries. This should be done prior to taking a trip where
you plan to use the tracklog to generate a return route. Clearing
the route of extraneous earlier logs will provide the most accurate
backtrack since less information will need to be analyzed.
Using a Tracklog
A tracklog of a mountain road can make you drive like a veteran. Once you have driven the road once you have a recording of all the twists and turns in the road. On the return trip you can anticipate the degree of the turns as they appear ahead. While turns may not be exact the information can still be valuable and certainly as good as the memory of someone who drives that route everyday. In addition you can watch the map display as an indication of upcoming turns that require decisions. You won't have to remember which way to turn at an intersection. In this way a tracklog becomes a very useful map for the trip. Be sure and keep your eyes on the road. You can't drive by looking only at the gps screen!
You can use a tracklog to visually generate a route manually. You can view the track and add waypoints at critical points directly on the map screen. Traveling the same route several times will cause tracklogs to overlap. This information can be utilized to visualize the effect of atmospheric errors over a period of time and may be useful in placing waypoints directly on the map page to average out the effects of these errors.
A primary capability of tracklogs is as the source of the automatic backtrack routing capability. Once the backtrack is generated it can be used to retrace your steps from one of the navigation screens. The tracklog is no longer needed to perform your return trip but can still be useful as an indication of minor turns.
Tracklogs may be used to prove you went to a particular location, arrived at a particular time, and traveled at a particular speed. All times are recorded as satellite times, not local times. A tracklog that is downloaded to a computer will contain this time data but not on upload. This way you are guaranteed that the log on the gps represents a real trip.
On the G-III, G-III+, etrex family, emap, and 76 family there are 10 saved logs in addition to the main tracklog. On these units saved logs can be used to provide updates to the map data for roads or trails that aren't on the map. They can also be used to extend the range of the main log or to save routes that are too long or complicated for the route capability. These logs are up to 256 points long (500 on the summit) and will automatically be reduced to 256 points from the main log if it is longer than that when you generate the saved log. You can turn the display of each of these logs on or off independently. The etrex will can only display one of the logs at a time. On all but the III family the backtrack function is actually done using one of these save logs.
To save a log in one of the named logs you should first collect the information you wish to save in the main tracklog. Then follow these steps:
Once you have a saved tracklog there are several things you can do with it. To work with a saved log you will need to select tracklog from the main menu and then highlight the saved log you are interested in. You can then:
Note that choosing backtrack on a etrex, 76, or emap will allow using points generated in the saved tracklog itself to perform a backtrack. There is no need to generate an actual route as required on the other units. You can directly traverse this saved log in either direction. There are up to 50 significant points saved in the tracklog that will be used for the backtrack navigation. (There seems to be more on the summit but the actual number has not been determined.) On the emap you can move your cursor over one of them and it will indicate a mappoint named "TURN" with a number. All of the turns have this label and while they can be seen in this fashion they cannot be selected. If you are navigating using a tracklog backtrack the significant turns will be indicated with a turn alarm (causing a beep on the emap if configured on). Significant turns seem to be turns of greater than about 60 degrees.
In other respects the emap, 76, and etrex backtrack navigation
behaves like a route navigation that is obtained on the other units.
An exception is that time and distance calculations are always made to
the final destination since there is no intermediate waypoints.
Uploading/downloading a Tracklog
There are many third party programs available that will permit downloading a tracklog. This permits saving tracklogs under different names and using them with pc programs. Many of these programs produce an ascii file that you can easily edit to shorten or modify in any way. You can also reload these tracklogs back into the Garmin unit. When uploading a tracklog the date and time data is set to 0 so it is not possible to upload a false track log. At least it is easy to verify if you do. Once you upload a track most units will automatically turn off track recording to preserve the log you just loaded.
You may want to upload a tracklog to restore a road map that you want to use for a particular trip. Or perhaps you could combine tracklogs to have several load roads or other track data. There are even programs available that will permit you do graphically generate a tracklog by tracing over a map. These can be used to build a lake outline or perhaps a shore outline. In this way you can have a simple map in units without mapping capability or to update a map in units that have one.
The Garmin III, III+, etrex, summit, and emap will always download the full log including all of the saved tracklogs. You can usually tell where the split is between the saved logs and the main log since the saved logs do not have a timestamp. There are two download/upload protocols available and if the program uses the latest one it will also get the saved tracklog names. Uploading can a bit more problematic since in the original protocol you could only upload to the main log. It was easy to create a download that is longer than the one you can upload. You would need to trim the download file and load it in pieces. Once in the main tracklog you can use the G-III to transfer it to the appropriate save tracklog. Using the latest protocol you can now directly upload into the saved logs by name which makes track log maintenance much easier. Note that the main log is called "active". You will need to check the program you are using to determine which method it supports.
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