XGPS160 - Consistent recurring accuracy drop

[MatthewS]

I've noticed the accuracy from my XGPS160 usually stays at 1.9m, but every few seconds it drops back to 3m for 1(?) sample. Any ideas what may be happening or how to fix/troubleshoot further?

I've attached a graph showing this drop and a screenshot of satellite view in App from same time.

Thanks!

[Harry]

Interesting, but I doubt one can answer this without insights into the GPS chip and firmware. So it is probably a question to Dual. Please keep in mind these accuracy values are statistic values only. The GPS chips derive a HDOP from the current satellite geometry, nothing else. This means a GPS position delivered can be off by dozens of meters and the chip is still reporting 1.9m. Atmosperic disturbances are one source of this type of precision degrading, but there are others too. LapTimer comes with an indicator for atmospheric disturbances named the Kp Index. It is available in GPS View. The higher it is, the less you can trust in the accuracy value shown.

- Harry

[gplracerx]

I don't think HDOP is a continuous function as reported. So what you're seeing is likely rounding error where the true HDOP is between 1.9 and 3. But, as Harry says, HDOP is a statistical estimate assuming standard conditions, which isn't always the case in the real world.

If you want to see what GPS location data can look like over time, see my post here. http://www.gps-laptimer-forum.de/viewto ... =19&t=1660