I am currently developing a little application in Android which uses GPS.
When i click a button i start to record a "track". If i walk around i save my position every second into a file. This works perfectly except for one thing:
I do not only save longitude and latitude but also the current altitude. Looking through the data I recognized that the altitude jumps some times.
For example the altitude values look like this:
271.4073616670083; 271.5165709069828; 345.6; 271.58538936056465;
The values around 270 metres are quite good. Jump like these happen irregularily but quite often (every 15 seconds there ist at least 1 jump). And the values always jump up to something around 340 metres.
While recording the track with my application I have also been walking around with an app called NMEA Recorder. This app recorded the altitude values as well but they don't jump like the values I receive.
I know that the altitude values of GPS (calculated by the WGS84-Ellipsoid) aren't very accurate but that still doesn't explain why the values jumpt sometimes.
Would be nice if somebody could tell me why jumps like these happen.