Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 19-05-2024, 13:09   #1
Registered User

Join Date: Dec 2014
Location: Aarhus, Denmark
Boat: Gibsea 33
Posts: 11
WMM variation being overwritten

I have been using the WMM plugin for a while, giving the correct value for the area. Now the variation value is being overwritten by variation included in received nmea RMC. Is this correct that it can be overwritten?

History is that I recently added a no 2 MFD to my stng network. I am receiving in Opencpn the nmea183 RMC string from the older RM a50.
Opencpn is not using N2k interface.
Faraway-dk is offline   Reply With Quote
Old 19-05-2024, 18:38   #2
Marine Service Provider
 
bdbcat's Avatar

Join Date: Mar 2008
Posts: 7,427
Re: WMM variation being overwritten

And are the WMM calculated variation and RMC provided variation significantly different?


Thanks
Dave
bdbcat is offline   Reply With Quote
Old 19-05-2024, 19:46   #3
Registered User

Join Date: Dec 2014
Location: Aarhus, Denmark
Boat: Gibsea 33
Posts: 11
Re: WMM variation being overwritten

Hi Dave
Thx for your reply
Yes, the variation was significantly different?
The correction should be around East 4.3 and was suddenly it was 0.4.

I discovered by realizing there was a constant heading error/offset.

I assume the wrong variation is a Raymarine issue, may be a setup thing between the Axiom and the A50.
When I setup the Axiom I checked that the auto-variation correction was exactly the same as calculated by WMM plugin.

I am just wondering why the WMM calculation is being modified/changed if Opencpn receives variation info from another source.
Faraway-dk is offline   Reply With Quote
Old 19-05-2024, 23:50   #4
Registered User

Join Date: Nov 2012
Location: Orust Sweden
Boat: Najad 34
Posts: 4,194
Re: WMM variation being overwritten

Quote:
Originally Posted by Faraway-dk View Post
I am just wondering why the WMM calculation is being modified/changed if Opencpn receives variation info from another source.
Plugin WMM is used if no source(GNSS receiver) reports a variation. If any real instrument does report a variation we assume it's a correct value. If the source is old and not updated by the user the device's inbound WMM table will give incorrect results.

If you can manually set the variation from the device to 0.0, or not used, OCPN will though use the WMM plugin instead. That's how this is solved by many using a dated device not applicable for a firmware update.
Hakan is offline   Reply With Quote
Old 20-05-2024, 00:04   #5
Registered User

Join Date: Nov 2012
Location: Orust Sweden
Boat: Najad 34
Posts: 4,194
Re: WMM variation being overwritten

Quote:
RMC string from the older RM a50
If that's the source for the bad variation and you still have position/SOG/COG from other source(s) you can try to filter RMC out if RM a50 is connected by its own OCPN connection.
Use "Ignore sentence" as described here
Hakan is offline   Reply With Quote
Old 20-05-2024, 00:36   #6
Registered User

Join Date: Dec 2014
Location: Aarhus, Denmark
Boat: Gibsea 33
Posts: 11
Re: WMM variation being overwritten

Hi Hakan
Thx for the clarification.
Now it makes sense. When I only had the old A50 connected it did not interfere, as it did not provide with a valid variation.
Does it mean, there is no need for the WMM if I can get my MFD,s to output a correct variation. Ocpn will then detect and correct the heading.?

If I over time will switch everything to N2k/stng, will Ocpn pick/use the variation if available?

/Leif
Faraway-dk is offline   Reply With Quote
Old 20-05-2024, 01:47   #7
Registered User

Join Date: Nov 2012
Location: Orust Sweden
Boat: Najad 34
Posts: 4,194
Re: WMM variation being overwritten

Leif..
Yes, Ocpn will then detect and correct the heading and thus not use plugin WMM, enabled or not.

If a valid variation is available by N2k it will be used, otherwise WMM as usual.

So I suggest you have WMM enabled all time.
Hakan is offline   Reply With Quote
Old 20-05-2024, 03:47   #8
Registered User

Join Date: Dec 2014
Location: Aarhus, Denmark
Boat: Gibsea 33
Posts: 11
Re: WMM variation being overwritten

Hi Hakan
Just disabled WMM in Ocpn.
Entered a manual variation in my Axiom, variation is transfered to the A50 and output as a valid variation in the RMC sentence.
Ocpn is correcting my compass heading. Nice.

Many thanks for help and advice.��
Faraway-dk is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Magnetic Variation (WMM) when boat is off the chart TacomaSailor OpenCPN 4 03-08-2015 12:50
WMM : new model EMM jean_pfoumf OpenCPN 6 20-05-2015 00:52
Variation Getting More Variable S/V Alchemy General Sailing Forum 20 07-03-2011 08:27
Deviation and Variation on Compass Sailaway Kid Navigation 8 02-07-2010 19:05
It's Official - 2010 Is 'Quit Being a Mariner and Start Being a Sailor Again' Michael D Meets & Greets 2 19-10-2009 15:59

Advertise Here


All times are GMT -7. The time now is 20:44.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.