Speed unit from gpsctl

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1

Hi,
I dont get the unit of the speed that I am getting from the RUT955.
I found another topic here, that says “normally” it is in knots. But how to figure out the unit ?
Is it knots for 100%?

Thanks!

2

You could inspect/compare the NMEA sentence $GPRMC which includes speed over ground in knots or $GPVTG which includes speeds for both knots (unit N) and Km/Hr (unit K)

3

How to do this?
Can you explain it a bit more detailed please

4

Okay got it.
But from where do I know which nmea sentence is gpsctl -v using?

5

I doubt the gpsctl -v speed is determined directly from a NMEA sentence as the raw speed is possibly m/s? However comparing the gpsctl -v result to $GPVTG fields you will have speed in both knots & Km/hr to compare to.

Run the following command
ubus call gsm.modem0 info|grep gps

Result will look something like “gps_port”: “/dev/ttyUSB2”

Then based on the result above run the following which will stream NMEA sentences
cat /dev/ttyUSB2

Look for a sentence starting with $GPVTG, the numeric value before the field N is speed in knots, numeric value before the field K is speed in Km/hr. Compare those to result of gpsctl -v

6

Okay thanks! But is that different for every device or is the output of gpsctl -v the same for every device ?

7

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