The first global positioning satellites were launched by the U.S. Department of Defense in the late 70s and now form a manmade constellation of 24+ satellites that works in conjunction with its ground stations to provide a worldwide navigation system.
GPS units are computerized receivers that obtain their information from signals transmitted constantly from the satellites. The satellites themselves serve as precision reference points and the system measures the precise time it takes the signal to reach the receiver. When the GPS unit has acquired signal contact with a minimum of three satellites, what amounts to a triangulation/ resection is performed and translated into a position coordinate, displayed on the GPS unit’s screen. (Each satellite has atomic clocks aboard, referenced to the United States Naval Observatory. GPS technology depends absolutely on accurate time and time measurement; that is why the time as displayed by a GPS receiver that has achieved a “position lock” is the most accurate time you’re ever likely to hold in your hand.)
Fortunately, selecting a GPS for back country navigation can be boiled down to a few basic factors. And the good news is that there’s no reason to spend more than $100 to $250.
If a GPS price tag runs much beyond $250, you’re not getting more GPS; you’re getting more bells and whistles. Let’s approach this from the standpoint of what you don’t really need in a GPS for back country navigation, because these are the features that jack the price up.
Now let’s talk about what you do need - or want - in a GPS.
First and foremost: a 12- or 14-channel receiver. Fortunately, this is easy: virtually all new GPSs are 12- or 14-channel these days. (This wasn’t always so and explains much of the bad press GPSs got in some articles and books in the early and middle 90s. They were dealing with pre-12-channel models that didn’t perform nearly as well in adverse conditions such as thick timber. (And while we’re on the subject, if your GPS is an old, pre-12-channel model, you’d be well advised to retire it.)
Second, a GPS that is WAAS-enabled is good idea and won’t affect the price much, if at all. GPSs that are WAAS-enabled can be accurate to within three meters 90%-95% of the time (at least in North America), while non-WAAS units are typically accurate to within 15-25 meters. It’s not much of a difference, but if the price isn’t impacted much, why not? (WAAS stands for Wide Area Augmentation System and refers to a series of GPS ground stations that broadcast data to supplement the data sent from the satellites, thus enhancing accuracy.)
Third, if you choose to use Terrain Navigator’s computer-generated maps, you’ll want to a GPS that offers - as a separately-purchased option in most cases - a cable enabling you to connect your GPS to your computer. Thus set up, you can transfer information from Terrain Navigator to your GPS and vice versa in seconds. (This information, mostly in the form of waypoints/landmarks, can also be entered manually; it just takes longer.)
In terms of brands, I see a lot of Garmins, Magellans, and Bruntons that people bring to my training courses and I own a couple of each. It’s Ford vs Chevy and more so every year; the main thing is to focus on the features and options we’ve just discussed.
In addition, a new GPS or one that has been transported a great distance must usually be re-initialized; more on that shortly.
The Map Datum issue starts out sounding complicated, but it’s something that is dealt with very quickly and simply.
Map Datums are of tremendous importance in surveying, mapmaking, and GPS use - they are the system or model that was used by the surveyor to relate the actual location of ground features to coordinates and locations on the map or system of maps.
Your GPS will offer up a very long list of options under “Map Datum.” What’s important here is that the Map Datum option you select for your GPS matches the Map Datum on the map - the individual topo - that you’re working with. New GPSs come from the factory defaulted to WGS 84 (World Geodetic System 1984), but because virtually every "store bought" USGS topo for the United States uses the NAD 27 Map Datum - I’ve yet to encounter one that doesn’t - select NAD 27 (North American Datum 1927) if you're using these off-the-shelf maps. If your GPS offers different breakdowns of NAD 27, choose NAD 27 CONUS (North American Datum 1927 Continental United Sates) if you’re in the lower 48 and, if you’re in Alaska, select NAD 27 ALASKA. (If you're in Alaska but your GPS doesn’t offer the NAD 27 ALASKA option, just stick with NAD 27.)
In any event, you can always double-check the Map Datum for your particular "store bought" topo. Every USGS topo map identifies its Map Datum, usually near the lower left-hand corner of the sheet.
In Canada, the situation is a bit more complicated, as the Centre for Topographic Information’s National Topographic System is currently revising all existing Canadian topographic maps (1:50,000 and 1:250,000 scale) from NAD 27 to NAD 83 (North American Datum 1983), which, for all intents and purposes, is identical to WGS 84. The principle is the same: always check the map you’re using and make sure its Map Datum is matched by the Map Datum setting for your GPS.
If you opt to use MapTech Terrain Navigator, you'll find that you can set the program's Map Datum for NAD 27, WGS 84, or NAD 83. Again, it's important that everything matches. If your GPS is set for NAD 27, select NAD 27 in Terrain Navigator. If you're running WGS 84 on your GPS, choose WGS 84 in Terrain Navigator. (The same thing applies to NAD 83).
The issue of how far a GPS is moved before a new initialization is required has a lot of variables. What I’ve found to work best is to fire up your GPS once you arrive in the general area of your new location in another province or state. If it acquires normally, you’re in business. If it needs to initialize again, it will be apparent right away and you simply perform the initialization process.
Basic GPS Operation
- It plots the instrument’s current position and identifies that position’s coordinate on the display screen.
- It marks (saves) positions - called “waypoints” or “landmarks” depending on the brand of GPS - in its memory. These positions are created and stored when the user is physically present and marks the position with his GPS, is physically elsewhere and enters the position’s coordinates manually, or transfers them electronically from a computer mapping program like Terrain Navigator to the GPS.
- It identifies the distance and bearings from the instrument’s location to stored positions, that is, “waypoints” or “landmarks.” (“Waypoints” and “Landmarks” are the same thing. For simplicity’s sake, we’ll refer to them as “waypoints/landmarks.”)
We see, then, that a GPS provides the same resources as map and compass: position plotting and direction finding. The key, however, as has already been pointed out, is to make your GPS work for you, combining its utility with other resources like map and compass.
I advocate a “turn it on, turn it off” approach to GPS. Turn it on, acquire your position. Use your GPS to determine a distance and bearing to a stored waypoint/landmark. (Usually by using your GPS's "GoTo" feature, which we'll be covering shortly.) Turn it off and shift to your map and compass. That’s it. This may seem like an oversimplification, but that’s basically all you need your GPS to do.
Now, let’s start to put it all together with map and compass, using examples, as we have done previously in the essay.
Marking (Saving) Your Position
To mark your position, begin, of course, by turning on your GPS. It will take your GPS a few minutes to seek out its satellites and achieve a “position lock.” Once it locks on to a minimum of three satellites, your GPS will identify your position as a UTM coordinate on the display screen. (In most cases, depending on make and model, the position coordinate will appear immediately. In others, you’ll have to cycle ahead through a screen or two to see the coordinate.)
Next you mark (save) your position as a waypoint/landmark, according to your GPS’s particular functions. You will be given the option of naming the waypoint/landmark; if you choose not to create a name, the GPS will automatically assign it the next number up in its memory. (Unless the name you assign a waypoint/landmark is specific and unmistakable, like “Camp” or “Truck,” use the number the GPS assigns the waypoint/landmark and keep track of what your numbered waypoint/landmarks represent in a small notebook. Assigning names like “tracks,” “spot,” “meadow,” “elk,” etc., in your GPS invariably leads to confusion.)
Figure 50 depicts an area on Cabin Creek in the Washakie Wilderness in northern Wyoming, where the current Grid-to-Magnetic declination - as confirmed by TopoZone at www.topozone.com - is 12 degrees east. We’ve saved a total of seven waypoint/landmarks - one named “Camp” and the others 1 through 6 - and plotted them onto the map, using steps described earlier in “Introduction and Map” section of the essay.
The map in Figure 50 reflects a common hunting scenario. Camp has been set up on Cabin Creek and the plan is to hunt the draws upstream both north and south of the creek. The waypoints/landmarks are outlined as follows:
Your major “return point,” - camp, your truck, etc. - should always be saved in your GPS as a waypoint/landmark and plotted on your map before you begin scouting or hunting. That way, you have the plot to assist you in map-and-compassing your way back in the event your GPS crashes.
Waypoint/Landmark 1 - 12 06 03 042
Waypoint/Landmarks 1 through 5 represent spots of interest encountered during the hunt or scout, such as tracks, droppings, rubs, beds, or anything else of significance. Once a waypoint/landmark has been saved (and notes taken concerning its relevance), you can pull it up on your GPS at any time and get an accurate bearing and distance to it. Out, then, come the map and compass and you can return to that spot, as described in “Compass and Direction Finding.” If the spot is of particular importance, plot it on your map. (Plotting your waypoints/landmarks on your paper map as you go is always a sound practice. It’s an important element of "Staying Found," which is simply defined: have a good idea where you are at all times.) And if your GPS crashes or is lost, because you have a UTM-gridded map that enables good triangulation/resections, you can switch over immediately to a map-and-compass navigation mode.)
Creating and Saving Waypoint/Landmarks,
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You can now transfer these saved "landmarks" (what we’ve been calling “waypoint/landmarks”) from Terrain Navigator directly to your GPS. And because you have them in Terrain Navigator, they will also print out on your UTM-gridded map, as shown in Figure 52.