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Index of Subjects Paul, I am curious where you learned that GPS uses atmospheric pressure for altitude. My GPS gives me altitude when it has good signals from 4 satellites. When it only has 3 it only give me position on the geoid. GPS receivers have no way to send anything to the satellites. Atmospheric pressure is important at airports because planes most basic altitude measurement is by pressure. Gerald Paul MacDonald wrote: > Hi Tom > Thanks for the info. I often wondered what those > things meant. > In addition I looked into GPS measuring of elevation. > I find they do so by atmospheric pressure. The GPS > sends that to the satelite which in turns takes the > pressure at the nearest airport and calculates the > elevation for the GPS. Seems atmospheric pressure at > airports is fairly important. > In this way weather variations are taken into account > - but if a weather system is going through Lunenburg > for example the Halifax airport reading will vary > somewhat. The claimed possible variation is 10 feet - > which is not too bad unless you are flying an > airplane! > An interesting subject. > Thanks again > Paul >
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