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Everyone interested in navigation must read this book
on September 10, 1998
The book's objective is to remove the mystery surrounding this new technology so that anyone who owns a GPS receiver can become an expert in its use. GPS Land Navigation has 6 chapters that cover everything from hardware (GPS, compass, altimeter), to software (maps, coordinates, bearings, etc.), to skills (trip planning, route finding, map reading, etc.) Three appendices contain: elevation, latitude and longitude of the highest points in each county; the coordinates of each state's capital building; and, the coordinates for the junction of every U.S. Interstate with either another U.S. Interstate or an U.S. Highway. You can enter this into a GPS receiver and use it a-priori to navigate to that specific location. The last appendix has detailed comparison information for every handheld GPS in production as of early 1997.
Chapter 1 Introduction to GPS discusses the NAVSTAR (U.S.) and GLONASS (Russian) satellite navigation systems. The NAVSTAR system includes 24 satellites and their coordinating ground stations. Each satellite carries four atomic clocks, and continuously sends radio signals, which GPS receivers use to calculate position. NAVSTAR is designed so that any location on earth will have line of sight access to at least six satellites at all times (as long as there is an unobstructed view from horizon to horizon). Simply stated, a GPS receiver determines its position by measuring the time it takes radio signals to travel from four satellites to the receiver. Each satellite simultaneously sends its precise location and software in the receiver triangulates these to get a fix. GPS receivers provide accuracy between 40 and 100 feet and chapter 1 provides an excellent discussion as to the determinants of precision and accuracy. Tidbit of information, GPS receivers are constantly updated by the atomic clocks in the GPS satellites, so as long as you have one you will know the EXACT time.
Chapter 2 GPS Hardware discusses the essential equipment needed for navigation. Surprise! GPS does not eliminate the need for traditional navigation instruments (compass and altimeter) but rather it complements them. A GPS receiver provides three essential pieces of data for backcountry land navigation: 1) position in terms of coordinates, 2) direction between any two waypoints, 3) distance between any two waypoints. This chapter gives you lots of information about how GPS receivers generate data. One piece of data that GPS receivers don't provide is actual directions on the ground. In most field applications, you need a compass to know which direction you are facing and which way to walk. Chapter 2 discusses baseplate, mirror, and sighting compasses. It explains how to obtain, set, and then follow a bearing (either from a map or a GPS). Finally, it summarizes magnetic declination, magnetic interference, and magnetic inclination. If you already know what these are, cool. If not, you'd better read the book. Finally, GPS receivers also display altitude, but for reasons discussed in Chapter 4, it isn't very accurate. So carry an altimeter and read the book on how to use it.
Chapter 3 Maps Maps are the single most important source of information in the backcountry. If you practice, you can guestimate where you are and get to another point using only a map and compass. If you plan in advance, you can navigate with only a GPS receiver and compass. However, with a topographic map, GPS, compass, and altimeter you can determine exactly where you are, plan precisely how to get anywhere with pinpoint accuracy, and even estimate how long it will take to get there. This chapter contains one of the best descriptions of maps that I have read. It covers all the classic things such as quadrangles, map-scale, distances, and various map series. Then it goes into some theory I had never really thought too much about. For example, did you know that maps and coordinate data from the continental U.S. are based on either NAD27, NAD83, or WGS84 datum? I never even knew such things existed much less why they might be important. But, you must tell your GPS receiver what datum the map you are using is based on. Chapter 3 introduces the concepts of angular (latitude/longitude) and rectangular (UTM) coordinate systems (whoa, no kidding, coordinate systems are critical) . This chapter also gives one of the most understandable descriptions (illustrated) of contour lines that I have read. There's even more. Chapter 3 tells you what all the information printed along the margins and corners of maps means. For example latitude and longitude are labeled at each of the four corners and are also tickmarked along the neatlines at 2.5 minute intervals (remember this you'll hear it again).
Chapter 4 Coordinate Systems may be a bit arcane but it's the meat of the book ("you can take the cheat or run the meat."). Simply stated, coordinate systems are the fundamental link between maps and the world they represent. Six digits of latitude and seven digits of longitude are all it takes to specify a location within 50 feet of precision anywhere on earth! A GPS receiver provide these digits. Unfortunately, merely knowing that you are at 34o35' 00" N, 084o12'30" W does not automatically translate to about a klick NNE of Cochran Falls in most peoples' minds. It does however if you grok coordinates. This chapter discusses angular coordinates and UTM rectangular coordinates in comprehensible terms (GPS receivers can be set to use either angular or UTM coordinates for navigation).
Chapter 5 Directions puts all the theory together. True North, Grid North, Magnetic North, Azimuths, Bearings, Great Circles, and Rhumb Lines all become clear and you are ready to go from anywhere to anywhere-else even if you don't know where either of them are relative to you.
Chapter 6 GPS Skills tells you how to use the theory. It explains how to use a GPS without a map, or with a map (which is what most of us do), and what to do when (horrors of horrors) your GPS receiver breaks down.