Harry's GPS Suite Forum

At my session yesterday, a very strange thing happened. For the first 10 laps or so, Laptimer was working normally, recording the information for each individual lap. Then, about midway through my session, I noticed it just kept a running tally of the remainder of my laps, all combined together as one giant lap. Needles to say, the information collected for the second half of my session was useless. I didn't touch my ipad at any time during my session. Any idea what may have caused this?

Most probably a shift in GPS positions over the day and triggers not set accordingly. To split your "lap" into individual laps, select it from Lap List and select Recalculate and Verify Lap. Select the Wide corridor when asked.

Harry

I followed the steps in your response, and it converted that combined lap from a time of 15+ minutes, to 0:32.33 (32.33 seconds), and didn't split it up into individual laps. So, I guess this data is lost.

Why would the GPS position shift during the day? With all of civilization dependent on GPS for everything from smartphone aps to military operations, I would think GPS satellite positioning would be one of the most stable and dependable parameters in the world.

Atmospheric influences shift the position received over the day. That's the reason track plots shown in Google Earth etc are often off (besides inaccuracy in Google Earth itself). This doesn't influence lap times measured too much because the shift within a lap is minimal, but it can go off quite a bit over a longer time. There are systems in please compensating this, namely SBAS and GBAS features. Consumer level GPSes (and anything up to 500 US$ belong to these) offer SBAS only. GBAS is by far superior as it allows local compensation. It requires a reference receiver and exchange of position gaps in near real time.

- Harry