Thank you. I have read more about the Elipsoid -geoid differences. That fits with what the customer was seeing.
Nathan On Thursday, September 27, 2012 5:51:23 PM UTC-7, Rudolf Hornig wrote: > > Hi, the 45m difference is quite plausible and it comes because of the > different 0 points used for altitude measuring. > > GPS is using the WGS84 ellipsoid as a reference for altitude, while people > (and maps) are using altitudes relaive to the mean sea level around their > location. The two reference point can differ as much as 150m in some places > of the Earth, tough the MSL - WGS84 difference is 40-45m in Europe. (It's > 41m here in Hungary). The altitude returned by the location change listener > is WGS84 relative... > As people usually expect MSL relative altitudes its usually required to > convert the two... The correction value is not provided by the android API, > but most handsets provide it in the NMEA sentences so you can pares it out > and use that value to correct the WGS84 value to MSL. > > You can check the MSL correction value in "GPS Status and Toolbox". There > is a small number near the altitude label. > Rudolf > > On Thursday, September 27, 2012 10:56:02 PM UTC+2, Nathan wrote: >> >> Once in a while, I get a message from someone in Spain or Italy that the >> altitude in my app is too high. >> Of course, I don't expect altitude from GPS to be terribly accurate. >> Then they'll say that some other app is getting better numbers. >> >> So I tried an experiment. >> Three apps running at the exact same time, stationary phone, all getting >> altitude from the GPS. >> They all showed different numbers. >> >> Actual altitude: around 398 ft. >> My App: 392 ft. >> MyTracks: 350 at first. Between 350 and 370 >> Another GPS App: 425. >> >> Mine was closest, through sheer luck I think. I know I am using Altitude >> from the Location. Since I register for location updates >4m I don't get >> any altitude updates when standing still. >> MyTracks, I looked at the code, I know it is recording the altitude >> directly. It does do filtering for stats but not the altitude itself. >> Other apps that are not open source may be adjusting the altittude, but I >> don't know what it is. >> >> Then the customer wrote back to say he was comparing against two other >> GPS devices (ie other hardware) and the phone GPS was consistently 45 m >> higher than the rest. While that's not good, it does make more sense. >> Unfortunately, I can't forget the experiment I did in the meantime. >> >> Any tips? >> >> Nathan >> > -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
