Positional accuracy and missed trigger points

[Cajundaddy]

Hi Harry,
I am a 10 year veteran of LapTimer/Petrolhead and I am seeing poor positional accuracy and 30% missed trigger points lately. Not sure what has changed. For many years I used iPhone 4S and then SE with Dual 5hz reciever, consistent accuracy of 1M and vey high reliability. Timing precision was usually within 1/10second which is plenty good for data analysis in both Time Trials on established race tracks or parking lot AX with SCCA or PCA.

Dozens of software updates and moving to the iPhone 6S over the years, positional accuracy has fallen off. I thought my 10 yr old old Dual receiver had become unreliable so I switched to the Dual Skypro 160 GPS. The best positional accuracy I can get with it is 3M and it will fail to start/stop a lap 30% of the time. I also notice many other Bluetooth receivers will interfere if in close proximity, most notably Racebox Mini which will cause LapTimer to miss a trigger point. How can I fix this and regain precision?

Details:
iphone 6S, iOS 15.8.3, xgps160,firmware 3.7.3

[Cajundaddy]

Hi guys, how do I get this approved by a moderator. I posted it back on Oct. 2 but it seems to have not been active yet on the site.

[Harry]

I'm sorry for the late reply.

LapTimer itself hasn't changed anything about sensor precision over the years. Internal and external sensors provide their measurements and these are taken 1:1 by LapTimer.

In situations like yours I recommend to start with the internal GPS and vary the position the phone is mounted in the car. Mostly, a center and frontmost position in the windscreen is best. In case your windscreen is metal coated or has heating / antenna embedded, a different position may be better. You can use the accuracy displayed as a first indicator (do it in an area without buildings / trees), but you will need to run a test lap to confirm a good position.

External sensors are almost always better. In case you phone connects to another driver's Racebox and you do not use a Racebox at all, simply disable that sensor in Administration / Sensor List to keep it from connecting. Raceboxes seem to use an extremely high transmission power, that's a frequent issue since they released their devices...

[Rolf205]

Hi,

I encounter the same issues. I'm using a Garmin GLO2 external GPS receiver and has been accurate for years, still same car, same track.
Now I swapped phones (Sony Xperia XZ2 Compact to Samsung S24) and now I miss trigger points (Start/Finish) and see in the GPS maps that I go outside of the track, have square corners etc.
Are there thing that I need to tweak on Android GPS setting or Bluetooth settings to make it work like on my previous phone?

[Rolf205]

An example:

Missing GPS update for 4 seconds:

[Harry]

Not to my knowledge. But it is clear that missing updates for that long can lead to missed triggers. As you get 10 Hz otherwise, it looks like either the connection is lost (and reconnected after 4s) completely, the device stops sending updates, or the Bluetooth connection is disturbed by some other BT device.

To investigate the first item, you can check the number of connections in Sensor List. With the Glo connected and delivering data (us the GPS View to monitor that for several minutes), change to Sensor List and select the Glo. This will bring up a dialog with sensor information including the number of connects since the start of LapTimer. This counter will increase by 1 every time you send LapTimer to background, but should not increase for other reasons.

[Rolf205]

Ok, I'll check that.
I don't think it is a failure of Laptimer, since it worked perfectly on my previous phone with the Glo.
Meanwhile I think it is the smart localization of Android, using other signals like Wifi to determine the position.

[Harry]

Smartphones use triangulation of WiFi and mobile networks to get a rough position in case GPS / GNSS is not available. While this is o.k. for many applications, it cannot be used for data recording apps like LapTimer. Both accuracy and update rates are far beyond what is required to e.g. detect passing a start / finish line.

So while this is a nice feature, a triangulated position will be ignored by LapTimer.

But in case the GLO connection drops, LapTimer will fall back to the internal GPS.

- Harry