Tuesday, October 12, 2010

The Incredible Brilliance Of The Conception Of Auto GPS For Direction Finding

By Kim Logan

One of the most frustrating things about going on a business trip is the travel to and from the airport. Almost by definition when you travel for business you are heading someplace you do not live. Even if you have been there before, road construction, traffic congestion and new hotels can make it a challenge to find your destination. The auto GPS solves that problem for us all.

Navigation has been an important science for mankind since before all continents were discovered. Since the oceans cover the majority of the earth, sailors needed some way to discern where they were once they had lost sight of land. Necessity being the mother of all inventions, the idea of discovering where they were on the ocean surface could be determined by sighting known stars in the sky.

With all the movement of the ships, it was not a very accurate method, but good enough that experienced sailors could cross the major oceans successfully. Celestial navigation, using the stars to identify the ship position was actually used mostly to confirm the position derived via dead reckoning. Since modern sextant sightings could only be taken at sunrise and sunset, owing to the need for a steady horizon, it was not very accurate either.

Using modern sextants, when sighting at sunset or sunrise, the measurement had to be taken over time to compensate for the up and down motion caused by swells and waves. Even when the process of sighting the heavenly bodies was perfected for use in aircraft, this time of sighting had to be preserved to account for the movement of aircraft. Since aircraft move much faster than ships at sea, the accuracy of the navigation techniques had to be improved.

The solution arrived at was the periscopic sextant, used up to and including the present day in military aircraft. The device is pushed physically through a portal in the top of an aircraft and locked in place to a mount that has an azimuth. It has a small bubble to help hold it level, and the star or sun is sighted through a two power telescope, with filters for the sun, of course.

When performing celestial navigation in the daytime, the star is obviously the easiest to find, but it yields only a single line of position, so it is less accurate than night celestial navigation. Using three stars located approximately 120 degrees apart in azimuth, it is possible to plot an exceedingly accurate position, even over the ocean, far from land. Unfortunately, the mathematical computations required are an acquired skill and the process is time consuming.

A tremendous step forward in navigation was the invention of the inertial navigation system, which operated by measuring the movement of aircraft in three dimensions. This technology allows for the collection of all the forces acting on the aircraft; thrust, drift and azimuth based from careful calibration of its starting point. It allows for accuracy in location many times better than navigating by the stars and dead reckoning, and can be accomplished by the computer, no navigator needed.

The final step in navigation progress came about with the satellite era. Since these man made celestial bodies have known positions and can be programmed to transmit signals with that information, a receiver on earth can determine the position it is anywhere in the world. Add computer overlaid maps and you can find your way road by road to places you have never been to before.

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