Guide to GPS
New advancements in GPS technology have made traveling easier than ever! You’ll never get lost again with step by step directions and path tracking. Handheld GPS receivers now even allow you to find your exact location anytime. Check out PE Facts to learn more about the benefits of GPS!
People are constantly on the move and are always looking for a better, faster, easier way to get to where they are going. A traveler without a destination is a wanderer, but even those with a map can have trouble getting to where they want to be. Especially in areas with few landmarks, travelers need a navigation system, or a means for determining their exact position, course and distance.
Throughout history we can see incremental improvements in mapping and navigation. With these improvements, people have progressively traveled farther, faster and with greater safety and reliability. During the last century, the pace of improvement in navigation and transportation accelerated exponentially. We even sent a man to the moon and robotic explorers to mars. We have regular missions into space, and satellites orbiting around Earth have become crucial to our everyday reality.
With our ability to send satellites into orbit came a new development in navigation. We can now map places with precision that was unimaginable prior to this advancement. This new navigational ability is due to the Global Positioning System (GPS), a system developed by the United States Department of Defense.
GPS was initially designed to assist ships and planes by providing specific navigational information, but advances in miniaturization and integrated circuits have allowed for GPS receivers to become more widespread. GPS technology now comes in many cars, boats, and even on construction and farm equipment. Portable, hand-held GPS receivers are also becoming easily accessible and are making many industries safer and more efficient.
How GPS Works
GPS consists of a network of 24 satellites and their corresponding ground stations. There are 21 primary satellites and 3 back-ups which orbit the earth in a predictable pattern at an altitude of roughly 10,900 miles. The satellites are used as points of reference to calculate an exact location within a few meters or better. Five tracking stations, located in various places around the Earth's equator, constantly monitor satellite signals.
A GPS receiver determines its location by solving a set of equations calculating the distance between it and three or more satellites. This calculation is an ancient surveying technique known as "triangulation." The travel time of radio signals between the satellites is what determines the location. At least three satellites must be available to get an accurate horizontal location, and at least four satellites are required to get an accurate horizontal and vertical location. The more satellites that are available to use for the calculation, the more precise the location can be identified. The Wide Area Augmentation System (WAAS) provides the most accurate determination of position. The Federal Aviation Administration's has now made this system the objective standard for all civil aviation.
GPS Signals
All GPS signals are in the L band of the frequency spectrum. Since L-band waves penetrate clouds, rain, fog, storms and vegetation, GPS units can collect accurate data in turbulent weather or beneath a forest canopy. Some situations where GPS units cannot get accurate readings are inside concrete buildings, in some mountainous regions or under especially heavy and wet forest canopies. Precision may also be affected by factors of both the satellite and the receiver. Eliminating all odds of inaccuracies is unfeasible, although corrections can be made after the fact. Despite the chance of inaccuracy, current GPS technology is outstandingly reliable.
The three types of GPS signals are: Coarse Acquisition Code, Ephemeris Data and Almanac Data.
Coarse Acquisition Code (C/A-Code) , is the most frequently used data received by a GPS unit, identifies the time it takes for the unit to get a reply from a satellite.
Ephemeris Data is constantly transmitted by each satellite to indicate the time, date and the practical condition of the satellite.
Almanac Data is an indication of the precise orbital location of the satellite and is transmitted to the five earth-based tracking stations that constantly monitor the GPS satellite signals.
Common Terms
Waypoint —Synonymous with landmark or coordinate, a waypoint is a location that can be entered and stored in the GPS unit at any time. Waypoints can be a final destination or be placed along the way to organize a route. They mark your position along a route and can be added or deleted at any time throughout a trip. You can begin with a start and end point, entering waypoints along the journey that deviate from the original plan. This gives you the liberty to roam and explore other interesting places without getting lost. Some GPS units allow you to give your waypoints names or symbols.
Go To —an express route to a place, such as a city or a specific address.
Route —a recorded path that illustrates how to get from one waypoint to the next. It is formed by connecting the waypoints that are entered into the GPS unit. The waypoints split the route into "legs."
Track back— the way in which the GPS unit records and stores your path or journey.
WAAS (Wide Area Augmentation System) —the technology that allows us to pinpoint a specific location within three meters or less. If you are looking for a high-level of precision, make sure that your GPS unit has WAAS.
GPS units are basically compasses with multidimensional accuracy. They are programmed with both magnetic north and true north settings; the user has a choice of one or the other. When using a GPS unit in conjunction with a compass, the magnetic north setting should be used.
The three types of GPS units that are typically used the most are: non-mapping, base-mapping and mapping.
Non-mapping GPS units are the simplest. They usually have no map detail. The plotter screen shows your path by tracking waypoints, routes or track logs. They may also display latitude and longitude and time of day, as a compass would.
Base-mapping GPS units are similar to non-mapping units in their plotting, tracking and route features, but they also display a map to help the user visually verify their location. If a map is not accessible but essential to find the final location, base-mapping units are helpful sources. Base-mapping units usually show state, interstate and U.S. highways, major thoroughfares in metro areas, airports, coastlines, rivers, lakes and exit locations. They can calculate your current location, speed and direction of travel.
Mapping GPS units have the ability to record the information entered and transmit it to a computer through an RS-232 cable. Mapping units can be personalized, depending on the amount of memory space, by uploading area maps or road maps from another digital source. Mapping units can be used for real-time applications. The amount of memory available may vary between mapping GPS units, so it is important to choose software carefully.
Getting Started With GPS
Before it can work, every GPS unit needs input data. The first piece of information that it needs to be aware of is its own location. When it is initially turned on, the unit will obtain a satellite signal to determine its starting point. After identifying the beginning location, you can track your waypoints as you travel. Tracking waypoints can build a guide for future travel along the same route. Some GPS units can record up to 700 waypoints.
GPS technology has developed far beyond the simple navigational assistance it was originally intended to provide, and improvements keep coming. New uses for GPS in work or recreation are just waiting for necessity or someone's imagination to discover them.
Please Note: The information contained in this publication is intended for general information purposes only. This publication is not a substitute for review of the applicable government regulations and standards, and should not be construed as legal advice or opinion. Readers with specific questions should refer to the cited regulation or consult with an attorney.
