Reading a GPS Display
I own a Sony NV-U44 GPS device, but these examples are from my old Garmin eTrex GPS receiver. Like most modern GPS receivers, you can choose how to display your coordinates. That is, you can choose degrees, minutes, and seconds or you can opt for degrees and decimal fractions.
For example, my location in a digital format, according to the display on my GPS receiver, is this:
N 42.96506 W 085.92599
Using the degrees, minutes, and seconds display, the following represents the same location:
42° 57′ 54.4" N 85° 55′ 33.6" W
That means I’m in the Northern and Western hemispheres. To be exact, I’m in this location:
42 degrees, 57 minutes, and 54.4 seconds north of the equator 85 degrees, 55 minutes, and 33.6 seconds west of the prime meridian That puts me in West Michigan. If you look at the digital equivalent of my location you can see how the 42 degrees, 57 minutes, and 54.4 seconds were simply converted to 42.96506:
N 42.96506 W 085.92599
The same was done with the second half of the coordinates. It’s 57 minutes of one way and 0.96 of the other. In other words, they’re the same coordinates, just expressed differently.
That’s important to know because you may see coordinates expressed one way, but your GPS receiver may be set to display them another way. Usually, you can make a quick conversion to the coordinates of your choice by going into your receiver’s setup menu and selecting Units or something similar.
Figure 2-5 shows how a GPS receiver display might look using the degrees and decimal degrees option, and Figure 2-6 shows the display when the degrees, minutes, and seconds option is selected. Note that these two readings do not show precisely the same location.
Figure 2-5:
The GPS receiver is displaying coordinates using degrees and decimal degrees.
Due to rounding errors, you may not get precisely the same values when you try to convert between the two types of display. It’s always best to pick one method and stick with it to avoid these types of errors.
Figure 2-7 shows one very good reason why you may prefer to use a GPS receiver that displays your position on a map rather than using latitude and longitude coordinates. I don’t know about you, but it’s a lot easier for me to determine my location by looking at the map display than by reading the coordinate display.
Figure 2-6:
The GPS receiver is displaying coordinates using degrees, minutes, and seconds.
Figure 2-7:
The GPS receiver is my current location using a map display.
Finding Your Waypoints
Waypoints are the essence of basic GPS navigation. At the simplest level waypoints are just the various points along the route between where you are and where you want to go. Even if you’ve never used a GPS receiver before, you’ve certainly used waypoints — you probably just didn’t use that name for them.
Understanding how waypoints work
To understand how waypoints work, consider the following set of directions:
1. Take Highway 395 south to the junction of Highway 341.
2. Turn left on Highway 341.
3. Turn left at the intersection with Cartwright Road.
Those directions seem clear enough, don’t they? Well, waypoints work pretty much the same way except that waypoints are often indicated using geographical coordinates in place of the names or numbers of roads or other physical objects. In fact, that same set of directions could be expressed using two waypoints (because the directions tell you to turn in two places) as in the following:
1. Go to N39° 24′ 10.1", W119° 44′ 46".
2. Go to N39° 21′ 59.1", W119° 39′ 59".
3. Turn left.
Although it’s true that both sets of directions get you to the same place, the directions that use waypoints offer one distinct advantage over the directions that use highway names and numbers. Can you spot the important difference? The first set of directions is pretty useless without additional information — such as an assumed starting point. The sets of directions using waypoints need no other details because anyone with a GPS receiver can follow them, no matter where the trip began.
Even though this example only uses two waypoints, that doesn’t mean that you necessarily want to set off on a cross-country hike directly between the two waypoints. You might find a number of obstacles in your path that prevent that sort of straight-line approach. If you use a GPS receiver that displays maps, you might want to choose the option to create a route that uses roads rather than to create a direct route. (The method for choosing this varies according to the type of GPS receiver you use.) But even if you choose the direct route option, your GPS receiver shows you the distance and direction to your next waypoint, just as you see in Figure 2-8. This means that if you have to navigate around a steep hill, a lake, or even a large building, your GPS receiver shows you how to reach the waypoint.
Creating waypoints
You can create your own waypoints a number of ways. The precise methods depend on your particular GPS receiver, of course, but generally you’ll probably find that you have at least some of these options available:
♦ Enter waypoints manually by entering latitude and longitude coordinates before you set out with your GPS receiver. This method requires that you know the coordinates, of course, but it allows you to set very accurate waypoints.
♦ The manual process may also be as simple as clicking points on an on-screen map. This generally won’t be quite as accurate as entering specific latitude and longitude values, but it’s far more convenient.
♦ Most GPS receivers allow you to manually set waypoints at your current location. This method is very handy if you’re out for a walk in a strange city and want to be sure that you can find the way back to your starting point.
♦ Many GPS receivers offer an automatic tracking option. Typically, this option creates waypoints at specific time intervals so you can later play back a record of your travels. If you use this option it’s a good idea to learn how to set the recording interval. That way, you can set a value appropriate to your mode of travel — shorter intervals for vehicular travel and longer intervals when you’re on foot.
Portable GPS receivers typically have a limited amount of available memory. If you set the recording interval too short you can lose your earlier recorded waypoints when the memory becomes full. As you can imagine, this could make it difficult for you to backtrack in unfamiliar terrain.
The popularity of GPS receivers has generated a whole new hobby — exchanging lists of useful and interesting waypoints. Web sites such as GPS Waypoint Registry (www.waypoint.org) are dedicated to collecting and sharing lists of these waypoints.
This topic has helped you understand a bit more about how to use your GPS receiver. Although there wasn’t room for an entire course on the finer points of GPS usage, I’m sure that you’re far more comfortable about how you can use your GPS receiver to get from where you are to where you want to be.
Figure 2-8:
The next waypoint is a half-mile to the northeast from my current position.
