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Issues with GPS accuracy

countersteercountersteer
in RaceChrono for Android
Phone: Samsung Galaxy S4, latest official Verizon OS as of April 2015ish
GPS: Qstarz Q818-XT
Latest version of RaceChrono Pro
Analyzed on computer with latest version of Circuit Tools

I did two autocross events with the above setup. The first event had 6 laps total over two sessions. In between sessions I turned off the phone and GPS. Morning laps yielded data that looked fine, but afternoon laps were all significantly (and seemingly systematically) offset in one direction or another. See imgur album here: http://imgur.com/a/SLA9g

The laps are also messed up in the RaceChrono app, so it's not an issue with Circuit Tools.

Someone mentioned that it was possible that there was an issue with resyncing the GPS/phone when I turned it on for the second session. So, for second test, I kept the phone and GPS on/synced the whole day. There are still issues with coordinates being offset or inaccurate. Here is what it looks like for 6 laps within an hour: http://i.imgur.com/IHHPNE0.png

Any ideas?

Comments

  • aol_of_RaceChronoaol_of_RaceChrono
    edited July 2015
    The changing "offset" is usually caused by anomalies in the weather conditions. Basically the GPS signals are distorted. The effect might be more noticable when locked to only few satellites. A better GPS might help, such as Dual XGPS 160 or Garmin GLO, as they can lock to more satellites at once.
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