COG, true HDG, mag COG all wrong

[did-g]

Originally Posted by codger

I can't blame OpenCPN for getting confused with conflicting data. Although certainly if it detected clearly incompatible data, in an ideal world it might pass on a message to the user that conflicting NMEA data are appearing.

So in this example there is a true heading (115), a magnetic heading (117) and a magnetic variation (16E) and by inspection it's clear there's a problem with something! There would certainly be an opportunity for OpenCPN to detect and report the conflicting data. On the other hand, I can see the argument that it's not its job to do this; garbage in, garbage out and all that.

Yes but O shouldn't mislead user, for example another issue :
If I use my phone as GPS it's sending RMC messages with a bogus magnetic variation of 3.3W, while wmm is displaying the real one 0.5W.

It doesn't matter here a 3 degrees error is a rounding one but it's not good.

[rgleason]

In the absence of RMC, would OpenCPN use the GLL position fix data to calculate COG/SOG?

I don't know, try it. Actually I doubt it will do that.

[oprlid]

Today I released a new firmware version for the tiny SeaTalk NMEA Link.
New firmware for the BridgeSD128, mentioned in this thread, will be available shortly.

I had a longer e-mail exchange with codger, and his explanations and logfiles helped a lot to solve the problems.

My problem is - I currently don't have access to to a boat with seatalk instruments.
So this firmware changes are tested on the workbench only.
I would need someone with a tiny seatalk-nmea link and a boat and the instruments that showed the problems. We certainly need some real word testing to verify this changes really solved to problems.

If someone out there is willing to test the new firmware, please let me know !
Again - it's not for the 128SD bridge, but for the smaller USB SeaTalk to NMEA0183 link.

Firmware can be downloaded from

Firmware :
https://www.gadgetpool.eu/nuke/downl...tLinkV1_73.hex

Firmware update tool for Windows :
https://www.gadgetpool.eu/nuke/downl...teTerminal.zip


The files are also available in the download section of https://www.gadgetpool.eu/nuke/index...ewlang=english



Changes are :

• Fixed calculation of COG for RMC, GLL sentence.
  Before : magnetic variation was ignored in calculation.
  New : reading Compass variation from Seatalk datagram #99 and from NMEA RMC sentence and included into calculations.

• Fixed VHW sentence.
  Before : VHW sentence was directly created from seatalk datagram 53.
  New : VHW data come from compass heading datagrams. Variation also included in calculation.

• Position in 1000th of a minute. Before it was 100th of a minute
  RMC/ GLL sends ddmm.fff before ddmm.ff

• When more precise data are available, don't send unprecise data
  (i.e. When receiving SeaTalk position with 1000th minute, don't use 100th datagram)
  Same with STW and Water temperature.

[rgleason]

The software update for Tiny Seatalk Link is also here
https://opencpn.org/wiki/dokuwiki/do...y_seatalk_link