Braille Live

GPS receivers: How they work
From space, GPS satellites transmit their signals to earth on different frequencies containing a multitude of data. It is the GPS receiver’s task to filter out these signals and convert them to data that can be used by navigational software such as Loadstone-GPS. To be able to do this, a GPS receiver is a powerful computer by itself. A complete GPS navigation unit therefore exists of two computers, the one in the receiver and the one on your PDA or phone.
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A Brief History of Navigation
Early man observed the sun and the stars, and presumably used these for navigation long before leaving any written records about it. As late as the Viking age (800-1100 AD), little further help was available for navigation on open seas. Rough estimates of the Polar star’s height over the horizon, together with ‘dead reckoning’ (from ‘deduced reckoning’, estimating distances from course, currents, winds and speeds), did not always suffice to find the intended destinations. With no instruments available measuring degrees was done ‘by hand’, 2 degrees for a finger, 8 degrees for a wrist and 18 degrees for a full hand. To measure speed, a buoy would be thrown overboard, a rope attached that had knots tied at regular distances. A sailor would count the number of knots that passed through his hands in a given time period as the vessel moved onwards, thus finding the vessels speed in ‘Knots’.
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