We all remember the days when we went on vacation and spent entirely too much time trying to figure out how to get to our hotel or the attraction we headed out to see. We have also had that sickening feeling of having an appointment or meeting to get to and encountering heavy traffic in an area we do not know very well. The incredible solution is the auto GPS.
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.
While celestial navigation can be performed on the open seas, modern sextants require there to be a visible horizon, from which the elevation of the star is measured, at sea this could only happen at sunrise and sunset, and the stars were not visible then. It is a myth that Polaris is the brightest star that shines and was used primarily to navigate the oceans. In truth the north star is not very bright at all.
What makes the north star special for navigation, is that when the elevation can be accurately measured, its elevation in degrees is the same as the latitude of a person making the sighting, eliminating a lot of calculation. The use of a periscopic sextant for aircraft has continued to the present time in some military aircraft, and while it is not as accurate as newer methods, it can still be accomplished if your aircraft loses power or the computers fail.
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 sighting the sun and stars through a sextant, you are attempting to find the aircraft location relative to the sub point under that star. The sub point is the spot directly below that star on earth, which moves as the earth moves. Through calculations, you can determine how close in nautical miles you are to this known spot, and then plot it on the chart. This information is compared with dead reckoning and pressure readings to determine the aircraft position fairly accurately.
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.
Kim Logan knows which is the best GPS for auto because she uses it daily to reach her customers. She likes to write auto GPS reviews for the best auto GPS units like Garmin nuvi models and TomTom One auto GPS.