BTStack GPS not recognized?

[robgendreau]

I have a jailbroken iPod 3g 8GB running BTStack GPS. I hook it up to a BT mouse GPS (BT338 from USGlobalSat).

It seems to run fine with MotionX and other GPS apps; they give me good accuracy.

But LT shows poor accuracy, a zero refresh rate, and lists 2Dcell/LAN in the box on the GPS display. I get no satellites in that view, and it says "no NMEA device attached." In settings it shows BTStack GPS as connected, but nothing coming through.

Have I missed something in setting it up??

Rob

[Harry]

Hi Rob,

As BTStack and the Satellites View is a interaction that is a bit tricky - but probably of general interest - I use this reply to give an overall description before going into your specific situation.

LapTimer uses the data delivered from the so called Location Service - a part of Apple's OS. It analyses the data delivered by checking if they are triangulation based (i. E. using mobile networks), or if they are GPS based. Only GPS based fixes are used for update rate calculation. In your case, LapTimer considers the position to be triangulation based and thus shows 0 Hz Update Rate. Other apps are not that picky and simply use triangulated data, LapTimer doesn't.

BTStack replaces Apple's Location Service and delivers similar data - although feed from an external GPS sensor. LapTimer currently does not change the way it acquires data when BTStack GPS is used - it is handled like native GPS data. This is the reason you see nothing in the Satellites View. The Satellites View requires data that is not part of Apple's Location Service. The only devices that are supported for the Satellites View currently are the TomTom car kit and G-FI. To support a device for Satellites View, I need to directly integrate with the device which is possible for these two. In this case LapTimer does not use Apple's Location Service at all and can deliver better and more extensive information (e. g. Satellites View).

So in your case we need to understand if GPS is really available. To understand this, please go into BTStack GPS and check if a relevant number of satellites is shown (compare picture in http://www.ringwald.ch/cydia/gps/). Switch back to LapTimer once you get a good signal.

- Harry

[robgendreau]

Thanks for the explanation; I'm getting 8 satellites per BTStack GPS and now LT is seeing them...I must have done a reboot or something in the interim so that it's working now. I can probably find an application I already have that will give me more sat data; LT doesn't have to do that. It's sufficient that it has a good fix and with the GPS mouse mounted outside the car it should work great.

For those who have BT GPS stuff already, getting an older iPod Touch, jailbreaking it, and installing LT and BTStack is a great way to go; thanks

Rob

[TomMurray]

Hi Harry,

Along the same lines, I've checked the Bad Elf GPS with LT and similarly, I can't get satellites showing in the GPS view.

In addition, I ran a test, one using the iphone GPS and another using the Bad Elf GPS along the same lap route. The iphone by itself showed better accuracy (approx 5m) when loaded to Google earth than the Bad Elf GPS (approx 10m). Is this accuracy difference due to LT not picking up the accuracy of the Bad Elf GPS or has it simply not aquired a good satellite fix?

I'm not sure how I can check the satellite fix of the Bad Elf GPS so can't see if it's got a good fix or not.

[TomMurray]

From the Bad Elf Forum:

Brett Hackleman

Our receiver is capable of accuracies as low as 1-2.5m (WAAS), although for various reasons I won't get into here, the iOS Core Location framework will report the accuracy as 10m even when it's better than that.


Harry,

I'm assuming this is why the accuracy through LT is at 10m, any idea if this can be changed to diplay correct accuracy?

Regards.

[Harry]

Along the same lines, I've checked the Bad Elf GPS with LT and similarly, I can't get satellites showing in the GPS view.

Please read the long post on the different integration levels of external devices above. The only devices that are supported for the Satellites View currently are the TomTom car kit and G-FI. The Bad Elf works fine with LapTimer, but details like satellites are not available currently.

- Harry

[Harry]

I'm assuming this is why the accuracy through LT is at 10m, any idea if this can be changed to diplay correct accuracy?

Yes, think so. However, I'm not aware that the Core Location framework limits accuracy delivered - but I guess that the Elfs know better. For all external sources other than the TomTom car kit and the G-Fi, LapTimer simply displays what the Core Location framework delivers.

Finally, do not take this too serious. Accuracy is not guaranteed in meters. The HDOP (horizontal dilution of position) is a statistic indicator relative to the chip's absolute capabilities. This final criteria is something we as hardware end users will most probably never know exactly. When LapTimer is connected to the TomTom car kit, it derives accuracy directly from the HDOP value. It takes a conservative approach here and will almost never show a value below 10m accuracy. I doubt it is not as good as the internal sensor's accuracy (which is calculated by Apple's Core Location service) on the other hand.

- Harry