GPS modems and heading when stopped

Comments: 6 - Last Comment by sbyram 280 days ago   Comment Filter:
Posted 282 days ago

Hi all,

Wow this font is really small...

Halton is getting Sierra Wireless MG90 modems.  Problem we are seeing is the heading reverts to North when the car stops.  These means the car symbol rotates on the map until the vehicle starts moving again, sometimes it is sideways across the road!  And if you rotate the map, the entire map rotates when the car is stopped.
Is anyone else seeing this behavior?  Please send your modem model if not.
Sierra Wireless says it's up to the application to ignore the headding when stopped....  maybe MPS product group can give their input!
Thanks for everyone's time,
Sarah Byram
Halton Police
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RE: GPS modems and heading when stopped
Posted 281 days ago in response to: sbyram

I took a look at a couple of TAIP specs (including one from the sierra website). I don't see anything about handling zero speed differently for heading. The TAIP protocol is different from NMEA in that it's positional rather than comma separated. I.e. when NMEA doesn't know the heading that field is left blank, but TAIP doesn't really have a choice but to put in something. I suspect that other models preserve the prior heading when speed goes to zero, but I don't know that for fact. I do understand that unless there has been some movement of the GPS that they can't determine Heading, i.e. Heading is derived within the device using multiple recent positions, there isn't a magnetic compass in a GPS device.

Do those new devices have the ability to switch to NMEA? That might be one solution. You can also file an SR and ask for a CR, but no promises on if or when there might be a code change -- it would be non-trivial because the various sentences get quickly collapsed to a common internal format in the MPS GPS library so it may be difficult to know when to ignore the 0 heading.

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