The Technology Of The GPS Transformed Navigation On Land And Sea, And In The Air

The earliest pioneers of navigation were seafaring people, who needed a means of identifying the position on vast seas, in order to make their way. They developed an ingenious means of using the sun to divine their position, crude but effective. These early navigators would have been astounded by the now commonplace GPS.

Even after aircraft were developed and man began to make journeys over the seas, the only means of determine the position of an aircraft was celestial, using the sun, moon and stars. The location of sun and moon relative to the earth has been calculated to the minute for every location on earth, and can be used for positioning. All one needs is a probable position and a sextant.

The methodology works fairly simply, once one is familiar with the science. For every celestial body, whether sun, moon or stars, there is a single spot on the surface of earth that is directly beneath it, that point is called the sub point. When the sun is directly overhead, not off to either side, one is standing in the sub point, but it changes second by second.

The entering arguments for the calculation are the sub point and the apparent height of this body. Using a presumed position on the earth (or above it), the known position the body occupies and the sub point, the apparent height can be calculated. The difference between this calculated height and what is the actual height provides positioning information.

For the exact time of the calculation, the body is sighted through a sextant, which provides the actual height above the horizon. The difference between the actual observed angle and the calculated angle is the result of a presumed position being either closer to or farther from the sub point. On a chart, each increment higher or lower translates to a nautical mile, and that distance is plotted.

By selecting three different celestial bodies, ideally at 120 degrees apart, the resulting plot is a triangle, the center of which is the actual position of the observer. Even after considerable practice, the calculation for three bodies and the sighting and plotting can take fifteen minutes or to resolve. While effective enough for airborne or seaborne navigation, it would never work for an automobile traveling on roads.

But technology always has an answer for these difficult problems, and it began with improvements in navigation for ships and aircraft. The steps began with automated celestial navigation assisted by computers, which cold do the calculations nearly instantly, then moved to inertial navigation systems, and then moved through a variety of triangulated signals from satellites.

Eventually the number of satellites and the level of computer sophistication made for triangulation that is continuous, and extremely accurate. Using a number of satellites, the accuracy of positioning an object anywhere on earth or above it has become astounding. Now people can enjoy not only knowing the real time position of their car while moving, but the relationship of the car to other things around them; the GPS has become ubiquitous.


To Get To A Destination One Must Know The Current Location Enter The GPS

The science of navigation was used first and most extensively by ocean going men seeking trade and exploration. In order to get around, it was crucial to have a good idea where one was, yet on the open sea, there are few geographic references near the coast, and none in the open ocean. In the absence of technology like the GPS they had to use the heavens.

Humankind has been studying the stars for as long as they have been noticed in the sky. Those who traveled the seas were, for a very long time, restricted to sailing within sight of land in order to determine their location. This was entirely unsatisfactory when travel across the oceans was attempted.

On a ship at sea, seafaring navigators could determine their latitude rather easily. While the North Star has been famously called in son the brightest star that shines it really is not, but it does have a unique characteristic. It is position in the heavens directly over the north pole of earth, a special gift to navigators.

In order to determine location derived from the north star, one triangulates from the angle of altitude above the horizon. Because of its unique position in the celestial sphere, the calculation were quite simple, and known to sailors as early as the 16th century. The angle above the of the horizon that one sights the north star is equal to the latitude of the observer, longitude was a more complicated issue.

Because the location of the stars, sun and moon are now tabulated in a book called the air almanac, printed since 1867. The data records the predicted location of 57 select stars, the sun and the moon in ten minute increments. From this information, ships and aircraft can calculate where they are based on where the celestial bodies should be.

Determining where one is relatively to the location of a single celestial body yields a line which technically circles the earth, and is used along with other information to determine a position. If three celestial bodies at near 120 degree angles are sighted, the position can be determined with much greater accuracy, though it takes minutes to accomplish even by a trained navigator.

The process is far too cumbersome too be used in vehicles traveling on roads across the nation. But with advancing technology, the process went from automated celestial navigation, then inertial navigation and finally satellite were launched to provide continuous active data to devices which can be mounted on vehicles or even carried by hand. The triangulation from three satellites can determine the position of the receiver with amazing accuracy nearly instantly.

With precisely position satellites beaming signals from space, devices in cars, aircraft and ships can quickly determine consecutive positions fast enough to also determine speed and direction of travel. Maps and charts are still a part of getting around, but technology provides so much more. With a GPS system, one can find not only the way, but what is along the way, and they are rapidly becoming a must have accessory for every vehicle.


The Navigator Now Found In Nearly Every Vehicle Is Powered By The GPS

The process of determining where one is physically located once out of familiar territory has been a problem for mankind throughout the ages. On land, one simply had to learn by the geographic features where one was and which way to travel to get to a destination. Thanks to the capabilities of the GPS, one can now easily fond the way from almost any point to any other with ease.

The first to make a concerted effort to identify a position without geographic references were the brave seaman of the early exploration age. Even ocean going vessels were pretty much restricted to travelling within sight of land. The urge to explore and develop trade with either nations drove the need to navigate over the oceans.

Over time, the sailors perfected a means of determining their latitude from the position of the stars. With clear skies, the mariner measured the apparent angle of elevation the North Star has above the horizon. It turns out that because the North Star is directly over the north pole, the apparent angle of elevation is equal to the latitude of an observer.

As navigators determined later, the same calculations can be used with any stars, the moon and the earth, and it could be done quickly enough to position a ship or an aircraft en route. The calculations require tables of data which calculate the position of sun, moon, and 57 selected stars. By determining how high above the horizon and at what azimuth the star should be seen from a location, one can determine a position comparing that information with the actual observed location.

If the celestial body is supposed to at a certain angle above the horizon, but the observed data is larger, then one is farther away than one assumed. This line, plotted on a chart, represent the location of an observer, but one needs more information to be sure. At night, celestial navigation can be more accurate. By selecting three of the 57 select stars at 120 degree separations, one can determine a much more accurate position.

These calculations require some time even for practiced navigators, and are effective only because it is possible for the aircraft or ship to travel in a straight line while the calculations are accomplished. But the accuracy of such a position is measured in nautical miles. Using them in a vehicle traveling over man made, turning paths like roads is not possible.

The technology began improving dramatically with the invention of computers. First automatic celestial navigation was employed. The next step was the use of inertial navigation equipment which measured the relative accelerations of a vehicle in three dimensions.

The pinnacle was reached with the invention of the GPS, a means to use preposition satellites to actively send data to receivers on earth, which can triangulate the signals and determine a position within meters rapidly enough to determine not only location, but speed and direction as well. Using the capability of computer technology, roads and other locations can be overlaid to find not only position, but highlight nearby locations as well.



