Miscellaneous Functions of Garmin Receivers

This is a collection of features found in Garmin receivers that are not especially connected with satellite navigation or unique to a small group of receivers. These functions may use satellite data and may be available on only one or a few of the models covered in this manual.

Celestial Data

Celestial Data includes Sun and Lunar data.

Sunrise and Sunset

This feature is found on all Garmin receivers. It computes the sunrise and sunset time for your location. On all units except the etrex it can also compute the sunrise and sunset times at other times and at other locations. The etrex shows this information as a selection field on the navigation page. The III family can show this information as a selection field on the position page. The III family can show this information for other locations or other times by using the planning feature on the route page. On other units the data is available as a selection option from the main menu.

From the main menu you select the Distance and Sun choice and the sunrise and sunset are displayed at the Destination location you choose. This page is intended to aid in planning a trip. You can use it to calculate distance for your trip as well as sunrise and sunset for any date you choose.

Sun and Moon

This feature is only found in the emap unit, the newest etrex units, the 76 family, and the GPS V. It can be reached from the main menu. You can view the sunrise, sunset, moonrise, and moonset for your day and position or for any other day or position you care to set up. In addition there is a visual picture of exactly where the sun and moon are at the time you set. The phase of the moon is also shown. Any of the top three data fields shown on in the figure can be selected and changed.

You can use the diagram of sun and moon positions as a crude compass if you can see either the sun or the moon. This can be done by holding the unit in front of you pointing straight ahead. Now rotate you body until the sun or moon is in the same relative position as shown on the drawing if you imagine that you are in the center of the circles. When you have the sun or moon located in the correct position you will be facing north.

Special III family features

A battery monitor

A selection field is available on most screens to monitor the battery voltage and time. Time will be reset automatically when you change batteries. You can also set the type of battery you are using to provide a more accurate battery gauge setting.

Trip Planning

The route page contains a trip planning feature. You can set fuel mileage and the planned date of the trip. You can build up a set of route points and use the selection field to view information about each one of them including sunrise and sunset at each point on the planned date. You can even plan your fuel stops.

Alarm Clock

While only the 12map contains an audible alarm any of the III family can set an alarm clock that will output a visual alarm at a preset time. Note that the unit must be on for this feature to work.

Special 12 family features

Surveying

While all Garmin receivers can use dGPS which can provide increase surveying accuracy with a suitable beacon source and any Garmin GPS can be used to provide for amateur surveying, the G-12 family has some special surveying features.

Area Calculation

The G-12 family can be used to perform area calculations. The idea is to traverse the area you are interested in and use the tracklog data to compute the total area of the track. The can be computed in acres and many other units and is available from the map page setup menu. There are a couple of things you should know.

Raw Data

While not documented, the G-12 family and some other Garmin models can be coerced into sending raw pseudo range data. This is the data obtained from the satellites prior to using it for a position solution and it can be used by post processing programs on a computer to correct for certain kinds of errors and permit better information about your position. This is the technique used by many Surveyors to obtain more accurate data. The idea is to hook the G-12 family unit to a computer and collect the raw data on the computer for later analysis. The G-12 cannot collect this data on its own. One source of a program is: Async Logger which can collect the data and convert it to survey industry standard RINEX2 (Receiver independent exchange) format.

The procedure to obtain this data is:

  1. Power on your GPS12 with a good view of the sky.
  2. Wait until a 3D fix is obtained.
  3. Run the async logger for a while (let's say 5 minutes):
    async -p your_port -a 0xffff -t 300 -o data.g12
  4. Run the parser with the option -rinex and redirect the output to a file:
    parser data.g12 -rinex > data.RNX
  5. Postprocess the RINEX file with postprocessing software.

You will need to find your own postprocessing software and a source of correction data. Pointers for this data can be found at the above site. Another source for this kind of processing is: Gringo.

The etrex family

The etrex summit and etrex vista contains two features that are not in any other Garmin unit except the 76S. One is inclusion of a built-in electronic compass and the other is the inclusion of a built in electronic altimeter. In addition they share some nice features with other Garmin models such as celestial navigation and area calculation.

Electronic Compass

The summit and vista have a flux-gate compass built in that can be used to obtain your direction while stopped. Standard GPS units can only indicate the direction of your movement which is derived from the standard GPS fix information. A flux-gate compass uses magnetic field information just like a standard magnetic compass and can be used independent of any GPS data in the unit. However, the power of a combined unit is the ability to automatically switch the source of information as suitable for the circumstances.

The first step in using this compass is to calibrate it. This is done by selecting calibrate from the main menu and slowly turning around two while holding the unit level. This may need to redone whenever the batteries are changed and may be required when the unit is located inside a vehicle. If you need to calibrate the unit for vehicle use you will need to drive the car in a circle twice. This step helps the unit account for any magnetic influences that may be present such as metal in the batteries.

Using the compass

The etrex summit and vista have marks along the center line to aid in using the compass to site a object. One way to use the compass is to select 'sight and go' from the navigation local menu (press the enter key). Then hold the unit up to your eye level and keep it level in the palm of your hand. Sight the object you are interested in using the sighting aids and then carefully press the enter key without disturbing the position. The position will be locked in and you can lower the unit to read it. You can use the arrow keys to:

If you chose either of the navigation options shown above you can use the local menu to select Stop Navigation when you are finished following the pointer.

When following the compass you need to keep the unit level for best accuracy. If you get it too far from level it will give you a message. Once you exceed a preset threshold the unit will switch from using the magnetic compass to using the GPS as the compass display. This is usually 10 mph but it settable as a heading customization option from the main menu setup options. You can also set the switch back time so that if you temporarily reduce speed the unit won't be switching back and forth too much. You can force the unit to switch between magnetic and GPS compass by pressing and holding the page key.

The system setup entries permit turning the GPS off if only using the compass or turning the compass off if only using the GPS. Using only one or the other can save batteries. The magnetic variation setting can also be set. You can set the output to read true north, grid north, or magnetic north from system setup.

NMEA output

The Summit/Vista can output the electron compass data via a standard NMEA sentence. This sentence looks like:

$HCHDG,A,B,C,D,E*chk

A = Magnetic sensor heading, degrees D.D
B = Magnetic deviation, degrees   not used on the summit
C = E / W                         not used on the summit
D = Magnetic variation, degrees
E = E / W                         To get True add E variation to reading
chk = NMEA checksum

Altitude features

The etrex summit and vista also have a built-in altimeter based on pressure changes. This is in addition to the altitude calculation that is performed as part of the GPS solution and can provide more accuracy. These units always use the altimeter for altitude readings and will always show a 3D solution even if you only have a 2D GPS solution. The altimeter altitude will be saved in waypoints and tracklogs. You can view the GPS altitude from a local menu item on the satellite page.

There is a special screen in the normal page rotation that is devoted to vertical navigation features. This screen will provide current elevation and an elevation profile similar the tracklog on the map page except that it is devoted to vertical movement. It will also display your vertical speed (ascent or descent). Selecting one of the two (on the vista) user selectable fields using the up/down arrow keys will permit choosing one entry from the following list: Local Pressure (renamed to Ambient pressure on new Vistas), Max Descent, Max Ascent, Average Descent, Average Ascent, Total Descent, Total Ascent, Min. Elevation, Max Elevation, (12 hour pressure trend for Summit), and for Vista vertical speed and normalized pressure (renamed to Barometric pressure on new Vistas). The 12 hour pressure trend can be used to help predict the weather. Normalized pressure is adjusted to show what the pressure would be if the altitude was zero (Sea level).

Be careful on these units that your don't cover up the barometric pressure sensor which is located on the back of the unit in the curved area. Note the small hole in the center. If you cover this with your finger the pressure sensor will not be able to work correctly.

Note that if you change your altitude the pressure changes and this is the way the altimeter works to display the changes in altitude. Thus the normalized pressure will change also since there is not enough data to provide independent information on pressure changes and altitude changes, given that the GPS altitude is not heavily depended upon. You can use normalized pressure to predict weather changes if you remain in camp. If you use the GPS solution to maintain altitude calibration then the normalized pressure will shift less which will improve its ability to record weather related pressure changes.

A local menu on this page can be used to reset the elevation data, the max elevation, or select whether you wish the profile display to show time or distance, (or a pure 12 hour pressure display on Vista). You can also use the local menu to select zoom to zoom the screen in either direction, distance/time or elevation. A view points option permits using the up/down arrow keys to scroll through the data. Press enter to leave any of these modes.

Similar to the ability to show a saved tracklog visually on the map page you can also show the tracklog vertical profile visually on the elevation page. This is an up/down arrow selection on the tracklog page.

The altimeter is generally expected to be automatically calibrated from the GPS altitude data, however you can calibrate it yourself if you wish. The main menu includes a calibrate option and you can select compass or altimeter. After selecting the altimeter you will be given up to three questions to calibrate the altimeter manually. These are: Correct the altitude?, Correct the pressure? or Use the GPS altitude?. Answer no until you get to the question you want and then answer yes to change the value. Note that the unit will display the current setting for each of these questions including GPS altitude for the last question so if, for some reason, you believe it is wrong you can answer this question with no as well and change nothing. (Note that this is a good way to view the GPS altitude, assuming you have a GPS fix of course.)

The automatic GPS calibration is not described in Garmin documentation but here is what I have been able to figure out. Above about 15,000 feet it will correct the altimeter once you have a lock fairly rapidly. On the ground it assumes you should be within 1000 feet of where the altimeter says you are and if the GPS altitude shows a bigger difference than that the unit will wait for you to correct it. Within 1000 feet it applies the GPS correction averaged over time and will correct half the error in about 22 minutes on an exponential curve that will eventually converge to the correct altitude. If you power it up with a different altitude after having been off for a while it will correct it in about 5 minutes. Of course if you don't have a 3D fix the altimeter altitude will be trusted to display a 3D solution. As a matter of fact these units never display the GPS computed solution and always indicate a 3D fix by using the built in altimeter. The tracklog also displays the altimeter altitude and this is what is used to display the vertical profile on the altimeter page.

The interface displays GPS altitude in the NMEA messages but the proprietary Garmin message displays the altimeter altitude. You cannot see the GPS computed altitude but it will be shown or if you go through the calibration process. You can cancel either activity, if you wish, after viewing the GPS computed altitude. (Note that early releases of the firmware used GPS altitude for waypoints but this is no longer the case.)

Other etrex features

The etrex Legend, Venture, and Vista contain a few more interesting features. For example they can be used to compute area and will product pseudo range signals similar to those already described in the 12 family. It can also show Celestial Data as described above and some unique features described below.

Area Calculation

The area calculation works a little different from the version in the 12 series. For instance it takes advantage of the saved logs to do its calculation so this can be saved. In addition it automatically sets the units for the area based on whether you have set metric or english measurements, but you can change the units after the calculation is completed.

Generally the etrex expects you to walk (or drive) the exact route you intend to measure and will then compute the area live, at the time you finish, by connecting the last point to the first point to ensure the area is closed, and then performing the calculation. If you have crossed over your track during your travels it will not be correct. However it also computes areas for any of your saved logs even if they were not intended for this purpose. This area information should just be ignored unless you know the log meets criteria of no crossovers.

But what if you can't walk or drive the route because of terrain problems? The etrex can also calculate the area of a route.

  1. Make waypoints of all 4 corners: a, b, c, and d. (or more if you wish)
  2. Turn the set of waypoints into a route but you need not close the last point.
  3. Select the route you just created and bring up the local menu. Select the route area to compute the area of the route you created.
  4. Note that it will not be correct if the route crosses over itself.

Any existing route can also be used to compute an area. Select the route and use the local menu to select the calculate area command. Units can be changed by highlighting the units and then selecting them to reveal a menu. Unless the route was specifically setup to compute an area it is likely to produce a meaningless result.

Calendar

The new etrex units have a calendar that can be used to display a date, jot down an appointment, or used as a method of reaching a particular period for celestial calculation or to find a best fishing time.

Hunt and Fish

The new etrex units can also calculate the best hunting and fishing times based on some undisclosed internal algorithm. It can be fun to calculate but don't yell at me if you don't catch a fish! While Garmin doesn't say how this is calculated you might find some answers if you study Solunar theory at http://www.solunar.com/TheSolunarTheory.htm.

Calculator

The etrex line also includes a calculator on the accessories page. It works like most other calculators that you might own and include % and memory functions for the standard calculator and can be switched from the local menu into a full fledged scientific calculator.

76 family

The 76 family is a marine unit. It contains many of the special features of the etrex family of products and supports WAAS. A unique feature of this unit is the ability to support depth data as well as altitude data. The unit also supports more alarms than most other units described so far including anchor alarms and depth alarms. The depth feature is accomplished by supporting the NMEA DPT input sentence from a depth sounder. The depth data in integrated into the unit alarms, tracklog, and is stored in waypoint data.

The Map 76S has a electronic compass and altimeter. These have the same features as the etrex vista unit described above. The altimeter in the 76S is a little more capable than the one in the Vista in that you can lock the altitude setting (for marine use) and cause the altimeter to behave like a traditional barometer. This is quite useful for weather predictions.

The altimeter/barometer in the 76S seems to be a better implementation than the one in the vista. For example the normalized barometric pressure (which is simply called barometric pressure) is cable of adjusting itself correctly even when altitude changes. The unit will need to be on for about an hour before this seems to work properly, however once calibrated is can be a help in accurate weather prediction. It is also more sensitive than the one in the Summit and Vista indicating changes of only 5 feet.

Note that the compass needs to be held horizontally for operation while the Map 76S GPS wants to be held vertically for best performance. This can sometimes compromise the combined use of these two features.

Notet that the 76S, like the etrex vista, reports altitude and saves altitude as calculated by the altimeter. However, if a waypoint is averaged on the 76S, then the GPS altitude is used.

GPS V

How about a game of breakout? This popular game is included in your GPS V in addition to a calendar, a hunt & fish calculator, Sun and Lunar data, regular general purpose calculator, and a gas mileage calculator which can all be reached from the accessories menu.

The Gas Mileage calculator is unique to this unit. It automatically uses your trip distance although you can override this with your own distance data. To use the calculator bring it up from the accessories menu and then enter the amount of gas your purchased. It will compute and display your gas mileage. You can even press the menu button to reveal a choice to note this information on your calendar. As a convenience this page will also let you reset the trip meter so that it will be accurate for a future mileage check.

The breakout game uses the rocker pad to move the paddle at the bottom of the screen. The object is to remove all of the bricks.

WAAS

To date only the latest released products from Garmin include WAAS capability (called EGNOS in europe and MSAS in Japan). This include the etrex: Venture, Legend, and Vista models, the 76 family, and the GPS-V. WAAS, Wide Area Augmentation System, is the latest method of providing better accuracy from the GPS constellation. It is similar in principle the the DGPS capability that is built into all Garmin units except that a second receiver is not required. Instead of a beacon receiver the correction data is sent via a geo-stationary satellite and is decoded by one of the regular channels already present in the GPS receiver. Thus one of the 12 channels can be designated to decode regular GPS signals or can be used to decode the WAAS data.

The way this works is that a set of ground stations all over the US collect correction data relative to the area of the country they are located in. The entire data is then packaged together, analyzed, converted to a digital correction format by a master station and then uploaded to the geo-stationary satellite, which in turn transmits the data down to the local GPS receiver. The GPS receiver then figures out which data is applicable to its current location and then applies the appropriate corrections to the receiver. The master station divides the country into a grid and then builds correction information on a per grid location basis from the data received from each reporting station. It is this grid location that is used by the GPS receiver to determine the applicable data.

In addition to correction information the ground stations can also identify any from the full constellation of satellites that is not working within specification thereby improving the integrity of the system for aviation use. The Garmin unit identified these Geo satellites on the satellite status screen by using numbers greater than 32. This system is just being set up now and will be improved with more satellites in the future (possibly 19 of them world wide), however since they are all geo-stationary you will need a clear view of the southern sky to use them from the northern hemisphere. This means they are very useful for an airplane or perhaps a boat, but less useful to someone on the ground. While a receiver can possibly receive satellite data from outside the ground coverage area there will be very little correction capability without the correct ground data. For more information see my in depth article on DGPS techniques.

Go to "Working with Garmin" Table of Contents

revision
00/9/2 original release
01/3/23 added stuff for new etrex models and WAAS
01/5/13 fine tuned some altimeter info.
01/5/26 upgraded vista discussion based on latest firmware
01/6/6 made altitude calibration clearer (I hope)
01/9/20 added some new etrex area calculation and hunt/fish
02/1/29 added 76 family and updated altimeter data.
02/4/11 added data on the latest etrex release.
02/06/14 added data on 76S barometer and some GPS V stuff.

By Dale DePriest: all rights reserved.