Hexagon Safety & Infrastructure - Post to topic GPS modems and heading when stopped

GPS modems and heading when stopped

2019-09-26 13:59:49 Etc/GMT

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

Ontario

RE: GPS modems and heading when stopped

2019-09-26 14:56:32 Etc/GMT

What sentences (and Protocol) are being processed by MPS? What are the contents when moving vs. stopped?

I'm not a GPS expert, but I don't think we've seen this, so it seems like Sierra is taking liberties, i.e. they may be within the letter of the spec, but not following common practice.

RE: GPS modems and heading when stopped

2019-09-26 15:41:07 Etc/GMT

Thanks so much Chip! Art from Caddo said he's pretty sure their tests with the MG90 and 9.2 didn't show this behavior.... I have asked which sentence they were using. We are using TAIP and I have attached a gpsarchive from a test drive.

When the speed is zero, the MG90 is reporting a heading of 000:

>RPV56745+4341314-0797406100000012;ID=6967;*70<

RE: GPS modems and heading when stopped

2019-09-26 15:42:19 Etc/GMT

We are 9.3 mr6

SOLUTION: RE: GPS modems and heading when stopped

2019-09-26 16:28:47 Etc/GMT

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.

RE: GPS modems and heading when stopped

2019-09-27 20:07:30 Etc/GMT

Switched to NMEA and the heading (Course in NMEA speak) is retained when stopped. Thanks Chip! Funny that SW said retaining the heading would be unreliable... HA!

$GPRMC,171951.000,A,4325.37262,N,07945.51816,W,000.1,313.9,270919,,,E*79

$GPRMC,171952.000,A,4325.37262,N,07945.51816,W,000.0,313.8,270919,,,E*7A

$GPRMC,171953.000,A,4325.37262,N,07945.51816,W,000.0,313.9,270919,,,E*7A

RE: GPS modems and heading when stopped

2019-09-26 16:58:51 Etc/GMT

Thanks for your time Chip! I will see what we can do.