GPS

Global Positioning System

The Global Positioning System (GPS) is a space-based global navigation satellite system(GNSS) that provides reliable location and time information in all weather and at all times and anywhere on or near the Earth when and where there is an unobstructed line of sight to four or more GPS satellites. It is maintained by the United States government and is freely accessible by anyone with a GPS receiver.

GPS was created and realized by the U.S. Department of Defense (USDOD) and was originally run with 24 satellites. It was established in 1973 to overcome the limitations of previous navigation systems.^[1]

In addition to GPS other systems are in use or under development. The Russian GLObal NAvigation Satellite System (GLONASS) was for use by the Russian military only until 2007. There are also the planned Chinese Compass navigation system and Galileo positioning systemof the European Union (EU).

Basic concept of GPS

A GPS receiver calculates its position by precisely timing the signals sent by GPS satellites high above the Earth. Each satellite continually transmits messages that include

§                     the time the message was transmitted

§                     precise orbital information (the ephemeris)

§                     the general system health and rough orbits of all GPS satellites (the almanac).

The receiver uses the messages it receives to determine the transit time of each message and computes the distance to each satellite. These distances along with the satellites' locations are used with the possible aid of trilateration, depending on which algorithm is used, to compute the position of the receiver. This position is then displayed, perhaps with a moving map display or latitude and longitude; elevation information may be included. Many GPS units show derived information such as direction and speed, calculated from position changes.

Three satellites might seem enough to solve for position since space has three dimensions and a position near the Earth's surface can be assumed. However, even a very small clock error multiplied by the very large speed of light^[27] — the speed at which satellite signals propagate — results in a large positional error. Therefore receivers use four or more satellites to solve for the receiver's location and time. The very accurately computed time is effectively hidden by most GPS applications, which use only the location. A few specialized GPS applications do however use the time; these include time transfer, traffic signal timing, and synchronization of cell phone base stations.

Although four satellites are required for normal operation, fewer apply in special cases. If one variable is already known, a receiver can determine its position using only three satellites. For example, a ship or aircraft may have known elevation. Some GPS receivers may use additional clues or assumptions (such as reusing the last known altitude, dead reckoning, inertial navigation, or including information from the vehicle computer) to give a less accurate (degraded) position when fewer than four satellites are visible.^[28][29][30]

Advantages -

Ø       The GPS is a tool that should supplement good map reading skills.

Ø       The GPS will make navigation easier and more precise over terrain that is not well mapped.

Ø       It can help one determine trail heads, side roads and generally make navigation more enjoyable when landmarks are not well defined.

Ø       It certainly provides a degree of security if one becomes disorientated (lost) and in an emergency situation it could make the difference in finding medical help quickly if a riding buddy were to become injured.

Ø       The more one uses a GPS the more one finds additional uses that make travel more enjoyable!

Ø       A GPS device is extremely handy. When you are hiking, you can deviate from a path without worrying about how you will find your way back.

Ø       When you are driving, GPS-based navigation systems can provide you with turn-by-turn directions, a helpful feature in a strange town.

Ø       Some GPS systems allow you to search the local area for nearby amenities, such as hotels, restaurants and gas stations. This is extremely helpful in some situations. For example, if you are driving cross-country and realize there is a problem with your car, you can search for nearby auto mechanics and select one that is along your route. Your GPS system will show you exactly how to get there.

Ø       GPS devices are perfect for water navigation. Since there are no landmarks in large bodies of water, boaters in the past had to use a compass and a map to determine if they were on the right heading, with somewhat imprecise results. But the advent of GPS systems allowed boaters to figure out their exact position on the map. In situations where underwater hazards are a problem, GPS devices allow boaters to steer around hidden dangers.

Disadvantages

Ø       From personal experience one can tell you that one can become "focused" on the GPS at the risk of not focusing on the road! It takes an effort not to become involved in the GPS over the map.

Ø       Map reading and navigation are skills that should come first and then the GPS used as a secondary means of navigation or confirmation!

Ø       The GPS needs batteries, external power, care and handling.

Ø       It can be another "thing" one must deal with at the cost of the freedom we all look for on a motorcycle. If you are a "free will" type person you may not even want to be encumbered with a GPS.

Ø       Possible failures can arise.You need to carry a backup map and directions in case your GPS fails for some reason. For example, if you are driving down a city street, the buildings may block the satellite signal, preventing you from receiving position updates.

Ø       Inaccuracy by the GSM. GPS signals are not completely accurate. Obstacles like buildings and trees can deflect the signal, causing your position on the GPS screen to be off by as much as 100 feet.

Ø       Atmospheric conditions (such as geomagnetic storms caused by solar activity) may also affect GPS accuracy. For highway driving, this can cause you to miss a turn or exit.