Tips and Tricks Waypoints are used to store and remember locations that are of interest to the user. They are often used to store intermediate turns and intersections that help define a route to a particular destination.
Similar to the waystations used by pony express riders as stopover points waypoints mark significant places on your journey. In some documents and gps receivers these may also be called landmarks.
Garmin receivers have differing capabilities in the number of waypoints that they can save. The earliest units could save waypoints while later models can store up to The GCX can save waypoints. In addition some units have additional waypoints that are stored in an internal database. These database waypoints are discussed in the chapter on databases.
Generally waypoint names can be anything you wish. On most unit they must be no more than 6 characters long and contain no spaces but can contain any combination of letters and numbers and some punctuation.
The newest units permits 10 character names and these can include spaces. The emap, 76 family, and etrex store waypoints in 3 dimensions by including altitude. All other units only store horizontal position. The 76 family will also store depth data for water if an optional depth sensor is attached. When you first create a new waypoint the unit will automatically assign it a name. These names are three digit numbers starting with and incrementing each time you create a new waypoint. Even if you rename a waypoint the unit will generally assign the next number in the sequence anyway and will not reuse the numbers until it reaches On some units it will automatically use the lowest available number but and on many others you can force the number sequence to continue from wherever you wish.
To do this just name a waypoint from the number sequence. For example naming a waypoint to explicitly will cause the next automatic number to be unless this is in use. It will automatically increment until it finds an empty number. Some folks assign a waypoint to a high number to force a block of numbers to be sequential for a particular use. Capturing your position as a Waypoint Storing your present location is the usual way to record a waypoint.
The location you were at the moment you pressed the button is already saved in the waypoint information on the form so even if you are traveling at 65 miles per hour down the freeway you can reliably capture a single point with the press of the button. A unique default name is assigned automatically but you can modify this name at your leisure without effecting the position data.
Finally you should hit "save" to store the waypoint in your database. The waypoint screen from the G family looks like: On some units there is an averaging feature. If you are standing still you can click 'average' on the waypoint save screen and the Garmin will start taking readings to average with the one that was captured when you hit the MARK key. Averaging will continue until you finally select save and enter.
While averaging is going on the unit will display a FOM, figure of merit, number to indicate the probable accuracy of the average to this point. On the G-III family and emap you first save the waypoint and then you can average by selecting this option from the local menu on the waypoint display screen. Please see more information on averaging below.
If you are using dgps you can still average the position but the improvement will be much less since dgps is already more accurate. Averaging still can reduce the some of the effect of a temporarily poor DOP. While averaging is going on you can move to the name field and enter the name you wish so that when you have achieved a stable FOM you want you can save the results.
Man Overboard All units except the aviation models, the etrex, and emap have a man over board MOB capability. This is accomplished by pressing the GOTO key Nav key on the 76 twice in a row and then hitting enter.
This will store a special waypoint at your current location named MOB and will automatically start the navigation features of the unit to aid you in navigating back to that point.
A position marked in this way is designed as a safety feature for boat use when someone might actually fall overboard. You may find other uses as well such as when your hat blows off you head driving down the road. If you want to save that location then you should rename it since it will be overridden by the next MOB sequence. Accuracy Considerations The accuracy of a particular fix is dependent on a number of factors. For example if the satellite geometry is poor the solution will be inaccurate.
Satellites close to the horizon will have good satellite geometry when coupled to one high unit but they suffer from atmospheric effects which can make the accuracy worse. These factors are taken into consideration when the unit reports the estimated position error, EPE on the Satellite status screen.
You should consult this information to determine just how good the fix is. Some other handheld units can also display this information using undocumented commands; see the chapter on secret commands for more details. The HDOP number is unitless where higher numbers indicate a worse fix. For a 4 satellite solution a 1. When there are more than 4 satellites available that can be used to compute a solution the older multiplex units will pick the best 4 for the computation.
They will also track 4 more so that as satellites move or the unit moves into new positions a selection of the best four can be made and switched as necessary. Switching to another set of satellites can, of course, effect the EPE accuracy. The newer 12 channel units automatically use all of the available satellites so they tend to effected less by this kind of change.
Using more satellites is called an overdetermined solution and can result in a DOP of less than 1. The meaning of Garmin's EPE number is not documented and it seems to vary for one model to another and even from release to release.
All of the data above is reflective of horizontal accuracy. This is primarily due to the difference the DOP for a vertical geometry. Many folks are disappointed with this level of accuracy since they often know their approximate altitude and can judge this inaccuracy much easier than they can the horizontal accuracy.
If you only have a 2D fix then the most recent altitude setting is used to compute the horizontal fix and if this altitude setting is wrong the horizontal position can be much further off. If you only have a 2D fix you should check and adjust the altitude manually as required to ensure an accurate fix. This can be set on the position page either directly by displaying and selecting it or on the G-III family and emap from the local menu.
If you augment your gps with a DGPS beacon receiver you can negate most of the atmospheric effects. As a result the accuracy of a DGPS is improved to 5 meters or less depending on the distance between you and the beacon transmitter. A beacon transmitter uses its precisely known location to correct for receive errors and then sends this correction data to your unit.
For DGPS to work you need to be able to receive some of the same satellites as the beacon transmitter so that a differential fix can be achieved. In the US the coast guard operates beacon transmitters which are available over much of the country with an effort currently in progress to cover the entire USA. Many countries around the world also have beacon transmitters. Unfortunately these kinds of services are not free. Please see the miscellaneous chapter for more details.
Averaging Techniques This section is a little more advanced than others in this chapter. Skip this section if your not ready to dig into accuracy issues. If you don't have a DGPS solution available you may still be able to achieve a better than 17 meter solution the Garmin spec by the use of averaging.
The idea of averaging is to leave the unit stationary and collect multiple solutions and then average them to obtain a better answer. This can be done with the unit itself, collecting data for later computer or manual analysis, or by hooking it to a computer and collecting the data in real time directly on the computer. If you want to average altitude data you must use an external computer since there are no altitude averaging functions inside any Garmin unit.
An exception is the emap and the 76 family. If you don't have an averaging function or can't stand still long enough to use and you still want to perform position averaging then use the tracklog. Set the sample interval so that the tracklog won't overflow in the time you want to average and let the machine collect the data. Depending on the model unit you have you will have , , or samples when the log is full. Any of these are plenty for our purposes.
The tracklog can be downloaded to a computer for analysis or you can perform an unscientific analysis right on the screen. Switch to the map screen and zoom in as far as you can while maintaining all of the points on the display.
Now use one of the techniques described below to place a new waypoint in the center of all of the tracks by visually weighing the distribution. This trick can also be used on tracklogs collected while moving. Suppose you keep a log of several days trips to work and back. You will be able to visually see a distribution at every turn in the route.
Assuming the log doesn't overflow and erase your previous trip you should be able to place a waypoint on the map page that is a reasonable average of the trips. You can selectively turn the log on and off to make this a usable method of obtaining an average using the machine itself. Similarly you could collect multiple waypoints over a long period and visually average them to obtain a better solution or use a computer to analyze the waypoints after downloading them.
If you use this technique be sure you take them several minutes apart and don't expect great accuracy unless you are willing to collect a lot of points. Averaging can be done even with a pencil and paper. Generally setting the grid to UTM can make this a bit easier but the idea is to record the location data every 30 second or every minute for a short while and then average the data you recorded.
Even 15 minutes of data will improve the location somewhat. Data recorded over a longer interval or will more separation is usually better so you could record several wapoints over several days or even weeks and average them later. Perhaps, if you have time, it would be wise to cancel the waypoint and start over. Waypoint entry can be entered several different ways without actually visiting the location or after the fact from collected data. There are several ways to enter a new waypoint but the most straight forward is to follow these steps: