Hi,

i've just purchased BTStack GPS and want to use it for track recordings with Harry's Laptimer Pro and a 4Hz Wintec GPS Receiver. During the first tests, i recognized that the Speed is jumping around (2-10km/h). Then i tested Navigon and there is the same issue. Also in the recorded data i've made, there are lateral G Forces on a straight track. With Navigon i could see that when you stop at a traffic light, the speed remains at approx. 15-20km/h and one second later goes to 0 and have the correct and fixed GPS Location.

The following Video on Youtube shows the problem with a Qstarz GPS Receiver (probably 10Hz): http://www.youtube.com/watch?v=FZjshKZHxms Thats not my Video, its just to show the issue!

any response ?!?

hi. BTstack GPS currently receives and uses only the actual position from the GPS receiver. To provide apps with speed information, it calculates the speed based on the time and distance to the last point. That seemed to work fine with standard 1 Hz receivers and should be fine too, when you're driving faster. If you have more samples, the accuracy decreases (at least with this approach).

I was informed that many GPS receivers also report speed themselves, so I plan on using those values directly in the next update. If there are no speed NMEA sequences, calculating the speed from a point 1s ago and the current one might give better data, too.

Can you try to reduce the update rate of the GPS receiver (somehow) and see if that helps?

i will try with 1Hz but i would appreciate the implementation of the "receiver speed" information to use 4Hz instead. Is there a release date for the update yet ?

no ETA. but I'll look into BTstack GPS after the Celeste 1.0 update which should be out in a week or so.

the latest 1.6 release has a switch to limit updates to 1 Hz