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As far as i know, there are only two ways to get altitude, by GPS or by barometer. GPS is not usable in indoor room, And iPhone5 doesn't have a barometer. But iPhone 5 can give a relative accurate altitude without barometer. How could it be possible?

  • In which app do you get this altitude ? – Matthieu Riegler Jul 6 '15 at 9:12
  • @MatthieuRiegler Altimeter – demonguy Jul 6 '15 at 10:15
  • Perhaps it's using nearby (known) locations and interpolating? – MrWhite Jul 6 '15 at 10:29
  • But I've tested at least 3 different apps, they all can get the same altitude – demonguy Jul 6 '15 at 11:12
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The iPhone does have two ways to get altitude, but the barometer is not one of them. You can only use a barometer for relative altitudes, not absolute, unless you know the current atmospheric pressure at sea level. But as well as GPS, Apple maintains a database of the locations (presumably including altitude) of a vast number of wifi networks, so if the wifi is enabled it can determine the altitude from the database. Try turning off wifi on your phone, and see if it can still get your altitude.

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    You're right! After turning off the WiFi and rebooting, i can't get altitude! But why?how does Apple get the altitude of WiFi hotspot? – demonguy Jul 6 '15 at 11:40
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    @w3d They're not GPS and barometer, they're GPS and wifi database. I'll edit to make it clearer. – Mike Scott Jul 6 '15 at 11:48
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    @MikeScott It doesn't make sense, I get an altitude at 1st floor, and go to 13th floor (at exactly same x and y position), i can also get the correct altitude – demonguy Jul 6 '15 at 11:52
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    @MikeScott If you have an accurate location for the Wifi point, and an accurate calculation of the network power, I think it's possible to calculate how high above or below the AP you are. Not sure though. – Nzall Jul 6 '15 at 18:31
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    You can do it if you have two, preferably three known altitude points in view at any given time… that's how GPS does it itself, triangulation based on various known points. – Tetsujin Jul 6 '15 at 18:50
0

All GPS sensors in our phones can determine altitude, just like it can determine your precise location, since GPS was designed to give 3D coordinate.

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