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Old 15-05-2022, 12:47   #1
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What NMEA sentence does GNSS compass use?

My system was working great - but now the GNSS compass of the dash board is non-functioning, even though I have 9 satellites showing from my GPS module. Before, I was getting GPS info from my AIS chart plotter. I looked in the docs but could not find what NMEA 0183 sentence the GNSS compass uses. Could someone clue me in?

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David
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Old 16-05-2022, 06:42   #2
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Re: What NMEA sentence does GNSS compass use?

Never mind - I finally found it in the opencpn manual.
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Old 16-05-2022, 07:39   #3
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Re: What NMEA sentence does GNSS compass use?

It uses the same heading sentences as a fluxgate compass
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Old 16-05-2022, 12:01   #4
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Re: What NMEA sentence does GNSS compass use?

It is normal that the "GNSS Compass" does not mark or erratic values come out if the ship is stopped.
The GPS "compass" angle is obtained with the COG, contained in the RMC and VTG sentences.
The COG is calculated as the angle between two consecutive coordinates (averaging several).

In any case, if you mean GPS/GNSS data in general, it is better to specify it as such and not as "compass".
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Old 16-05-2022, 16:48   #5
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Re: What NMEA sentence does GNSS compass use?

Quote:
Originally Posted by Tehani View Post
It is normal that the "GNSS Compass" does not mark or erratic values come out if the ship is stopped.
The GPS "compass" angle is obtained with the COG, contained in the RMC and VTG sentences.
The COG is calculated as the angle between two consecutive coordinates (averaging several).

In any case, if you mean GPS/GNSS data in general, it is better to specify it as such and not as "compass".
A proper GNSS compass obtains heading info using two gnss antennas and computes the phase difference. It does not use COG. It can give a reliable and accurate heading even motionless.

I know cause I have one. ( hemisphere sat compass )
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Old 17-05-2022, 03:29   #6
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Re: What NMEA sentence does GNSS compass use?

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A proper GNSS compass obtains heading info using two gnss antennas and computes the phase difference. It does not use COG. It can give a reliable and accurate heading even motionless.

I know cause I have one. ( hemisphere sat compass )
Yes, I know that this expensive system exists, but it is not common.
In the OP's subsequent comments, it seemed to me that this was not the case.
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Old 17-05-2022, 05:40   #7
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Re: What NMEA sentence does GNSS compass use?

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Yes, I know that this expensive system exists, but it is not common.

In the OP's subsequent comments, it seemed to me that this was not the case.


Not expensive any more since U-bloc have released an integrated solution. I expect they will be several marinised versions soon and the days of the fluxgate are numbered.
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