1 - How it Works
The GPS system was originally developed by the United States Department of Defense for military applications; however, today this system is used, free of charge, by anyone with a GPS receiver unit to track their own position on earth. The Global Positioning System is a satellite based navigation system consisting of 24 satellites orbiting the Earth at 12 hour intervals. Signals from these satellites make it possible for people on the ground with receivers to pinpoint their geographic location by a system of triangulation. GPS devices use a receiver to acquire signals from at least four of the GPS satellites. Using these signals the GPS receiver is able to gauge the latitude, longitude and elevation of the user. The GPS receiver can overlay this information onto map files stored on the unit, revealing the user’s current position on the map. Since the receiver is constantly recalculating its position relative to the satellite's position, the GPS unit can track the user’s location in real time.
Most general-use GPS receivers can locate your position with an accuracy of around 10m. The quality of the receiver and your geographic location will determine how long it takes the device to get a fix on your position. GPS receivers require a clear view of the sky to get a fix on your position. It’s therefore harder for the receiver to lock onto and hold a signal if you're traveling through a dense forest or an urban area with tall buildings. |
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GPS devices for consumers are generally available as an add-on accessory for hand held devices such as pocket PCs and PDAs; as stand-alone devices; and as navigational systems built into dashboards of high-end automobiles. If you will just be using GPS while driving or boating, a dash-mounted device should suffice. If you go hiking, or boating, a handheld device or a stand-alone device will suffice.
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2 - Types of GPS Receivers
As mentioned earlier there are a various types of GPS receivers each designed/suitable for a specific task. There are handheld receivers, suitable to be carried around while traveling; there are devices that are embedded in wristwatches, suitable for bikers and hikers. There are devices that can be plugged into PDAs, suitable for those roaming in the urban jungle. There are also devices that can be fitted onto dashboards of automobiles or boats, suitable for navigation in unfamiliar territory.
2.1 - Handheld
A handheld receiver is as small as a cellular phone. It provides the user with details of its location in the most basic
form of longitude, latitude, elevation and time. Handheld receivers are suitable for hikers, mountaineers, and explorers
who like to venture into uncharted territory. These devices are light weight and consume very little power.
2.2 - Car Navigation
Car Navigation GPS receivers is one of the most popular forms of GPS receiver. Most car navigation units can store designed
maps of select cities & locations and map them with the co-ordinates received from the satellites to give the user a
graphically defined way of his journey. Most of the in-car units are free of keypads or input, other than a touch sensitive
screen. They provide spoken turn-by-turn directions keeping you focused on the driving, while the GPS takes care of the
navigation.
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2.3 - Palmtop Navigation
Some GPS Receiver modules plug into the extension port on the PDA. For the traveler who owns a PDA, adding this module reduces cost
by eliminating the need for buying a separate receiver. At the same time it offers the convenience of having to carry one less
device. Detailed maps of towns and cities can be installed on PDAs making the process of gauging locations simple.
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2.4 - Wrist GPS
Technology now makes it possible to pack a powerful GPS receiver into a device wearable on the wrist. For runners, bikers
and backcountry travelers, these units are a great way to navigate and track their progress. Though these devices
don’t support GPS mapping capabilities, they do offer route tracking, as well as distance, altitude, speed and
location data. Quite a few of them offer PC connectivity, as well as software that tracks and organizes trip data.
2.5 - Marine GPS
Marine receivers are used by large and small boats. These receivers offer the same functionality that is offered in the
car navigation receivers. However these receivers do not have any downloadable maps and cannot give a graphical guidance
to the user. These are used to ascertain ones position on open waters.
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3 - Purchase Factors
3.1 - Suitability of Use
A variety of GPS receivers are available in the market. Choose the one that is suitable for your specific task.
For example, you could choose a GPS receiver that is wearable on the wrist for tasks such as hiking or biking; or a
GPS mounted in the dashboard for car navigation.
3.2 - Receiver Type
The receiver type is defined by the number of channels that the receiver can collect data from to determine its position.
A channel carries the data that is being collected from a single satellite. The most basic of receivers supports 8 parallel
channels. What this means is that it can scan for 8 satellites to determine its position. The more channels a receiver can
scan, the greater is the accuracy of the position arrived at. The max number of channels a receiver supports is 16. A
receiver that scans 16 channels can provide 95% accuracy. For applications where you do have a clear view of the sky
choose a receiver with at least 12 parallel channels
3.3 - Display
Choose a GPS model with a good color screen that can be read in all lighting conditions. Large screens provide users with
larger image, improving the readability of maps being displayed. Check the viewing performance of the display to make sure
you can read it from any angle. This is an important feature to check for in GPS receivers built into the dashboard.
3.4 - Water Resistance
Few GPS devices are completely waterproof, but some offer a measure of water resistance. If you plan to use your GPS in a rugged
environment or while boating, look for units which have a level of water resistance. In case the receiver is not water resistant
care has to be taken to protect it from water seeping into it, as water seepage can damage such units |
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3.5 - WAAS
GPS receivers have an accuracy of about 10 meters, but you can get to as close as 3 meters with a WAAS-enabled receiver. WAAS
stands for Wide Area Augmentation System. Wide Area Augmentation System is an array of satellites and ground stations that
provides GPS signal corrections. These correcting signals improve the positional accuracy of the GPS Receiver, which averages
up to five times more than non-WAAS units. A WAAS-capable receiver can provide a position accuracy of better than three meters,
95 percent of the time.
3.6 - Long Battery Life
The last thing you would like to happen, when you are lost and searching for a location, is the battery of the GPS receiver
dying out. Ensuring a long battery life is a priority. GPS units having battery-saving qualities keep you from having to invest
a fortune in batteries. Some units with 2 batteries have a longer operating life than some with 4. If you will be out for long
make sure you carry spare batteries with you
3.7 - Maps
Most GPS receivers come with only the base map. Look for a model that includes street-level maps. Some manufacturers charge extra
to unlock maps from their Web sites or CDs. This can get expensive if you want maps of larger regions. You may need to add or
update maps at a later date, therefore make sure you can update the unit's firmware and mapping data. Most portable units have a
USB or serial port that lets you connect the system to a PC, where you can upload the latest maps and system software as it
becomes available. On in-dash models, maps are typically read from an integrated DVD or CD player. A GPS receiver is a must have
for adventurers who move into uncharted territory and the executive who travels between cities and those who are directionally
challenged. With a GPS receiver on hand, you never, ever have to fear getting lost!
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