How is Course Over Ground calculated

Hardware Pixhawk family
1

Hi,

How is Course Over Ground calculated?

is it an instantaneous reading from that exact sub-second only; or is it based on what the plane is doing before and after a given sub-second?

thanks in advance!

Jeff

1 Like
2

To what “Course Over Ground” are you referring? Is it something you see displayed in your Ground Control Station? Or perhaps something from a log? (If that, which log?) Or is it somewhere else?

3

hi,
thanks for responding.

when i extract data from *.tlog, i select the “mavlink_gps_raw_int_t.cog”.

thanks again

4

I have not looked this up before, so someone else please correct me if I’m wrong!

From reading the source (the calc_blended_state() method of AP_GPS.cpp) I believe that field records atan2(gps_velocity_east, gps_velocity_north). So that might be enough detail for you: The ground course is the magnetic direction of the GPS velocity.

If you need to know exactly how the GPS velocity is calculated (is it filtered? Is it a simple backwards-difference? What happens to it if the GPS loses or gains satellites, changing it’s position estimate? Does it utilize a GPS’s ability to measure the doppler shift for more accurate velocity measurement?) it seems that probably depends on the specific GPS.

Does that help?