Beta Test / Technical

[Hakan]

Dave..
It may be that I understand why the VDR play didn't work. There where no HDM/HDG message.
Also if I understand the coding right you ad the mVar to the magn. heading to create a true heading from the HDM message only? That can be a problem.
When I today installed my compass into the Simrad IS15 system I learned that even if the compass sends HDM to the IS15 inner system the IS15 system later put that value in a HDG message and distribute that to the "outer" world like OCPN. So an HDM is never visible in OCPN but a HDG without Head_T but only the Head_M (Pos.1).
Anyhow... I'll make a test tomorrow. (Now soon 24h here)
Håkan

[Neptune's Gear]

Hi Guys, I'm trying to track down an issue where my boat ICON jumps back and forth between Mag and True, but the dashboard heading data is stable. Is what you are doing related?? (Latest beta version OCPN)
Thx

[bdbcat]

Hakan...

New code in github now.

1. Corrected MSVC build error. Sorry.
2. Calculate HDT from HDG, as you require, I think.

By the way, HDG does not have True head in the message. It contains only HDM, deviation and variation.

Good Luck
Dave

[bdbcat]

NeptunesGear...

May we see a screenshot of your NMEA Debug window?

Thanks
Dave

[Neptune's Gear]

Absolutely. I'll make on tomorrow and get back to you. Thanks.
Matt

[Hakan]

Originally Posted by bdbcat

Hakan...
New code in github now.
1. Corrected MSVC build error. Sorry.
2. Calculate HDT from HDG, as you require, I think.
By the way, HDG does not have True head in the message. It contains only HDM, deviation and variation.
Good Luck
Dave

-Thanks Dave you are really productive. Now nicely built without error nor warnings.
- Yes the HDG messages is transmitted from Simrad instead of the HDM. I've now been in the boat testing but unfortunately no success.
I couldn't debug because I don't have the source for the WMM and therefore no debug set up. I'll find the source and try again.

If you would want to try yourself there is a half an hour VDR record from my on-board installations. But the file was to big for this forum so please download by right click "save as" from this link:
https://dl.dropboxusercontent.com/u/...st_VDR_rec.txt

Håkan

[bdbcat]

Hakan...

Thanks for the trace log.

I see the trouble.
In the log, the HDG sentence contains an incorrect Mag variation.

$IIHDG,307.0,0,E,0.0,E*53

This sentence says the variation is 0.0. Opencpn has no choice but to accept that value.

Same is happening on the RMC message:

$IIRMC,103344,A,5805.559,N,01143.861,E,0.0,0.0,,0.0,E,A*04

Variation is 0.0 E

I would have expected the $II system to send a message more like this:

$IIHDG,307.0,,,,*xx

That is, variation and deviation are unknown, so not sent.

Maybe there is some configuration option available in your $II system?

The WMM value is available to Dashboard, but is not used, since it is hard-coded to a lower priority than the NMEA stream. Of course, we could change the WMM to top priority, and this would fix the problem for you. But that does not seem right, somehow. WMM is a theoretical estimate, as are the values send by a GPS. On my systems, they often are not the same, sometimes off by a degree, or so.


So, not sure how to handle this.

Ideas, anyone?

Thanks
Dave

[Hakan]

Dave..
Very good - I mean at least something traceable!
First-- The Simrad also send the "VHW" sentence including headings and it seems that the code check this first??. So the coding:

 //      If Variation is available, no higher priority HDT is available, 
                //      then calculate and propagate calculated HDT
                if( !wxIsNaN(m_NMEA0183.Hdm.DegreesMagnetic) ) {
                    if( !wxIsNaN( mVar )  && (mPriHeadingT >= 2) ){.................

may fit there as well?? (the mPriHeading is lower there??)

Second-- I think It's my old GPS Garmin 120 sending the variation 0.0 because its table is far outdated. This is from the GPS:
$GPRMC,103345,A,5805.559,N,01143.860,E,000.0,360.0 ,140214,000.0,E*79
Simrad IS15 reads from the GPS and put the value in its HDG. And thats rather fair since the variation could have been "0" as it was here a couple of years ago.

But............
In the VDR record file the variation is 3.0 for a while since I stated that in the GPS. (Around row 6500) and still is the true heading not printed in OCPN.

I'll force the GPS to show nothing instead of 0.0 but the 3.0 value should have been good enough?
(And by the way....you earlier changed the code to init mVar to "NAN" instead of "0" ---why?)

Please excuse my "silly" questions but sometimes it can help - if not just lay them apart.

Håkan

[Hakan]

Dave..
For additional tests--I've edit the VDR file so that all 0.0,E are gone but instead reads: ,,E. https://dl.dropboxusercontent.com/u/...st_VDR_rec.txt

But... the checksum is then no longer valid!!! --- I play in one PC and send it all out on the net to the debug-PC. And there I can click away the "Control checksum".

And still no true heading - sorry

Håkan

[Hakan]

Originally Posted by bdbcat

Hakan...
..........The WMM value is available to Dashboard, but is not used, since it is hard-coded to a lower priority than the NMEA stream. Of course, we could change the WMM to top priority, and this would fix the problem for you. But that does not seem right, somehow. WMM is a theoretical estimate, as are the values send by a GPS. On my systems, they often are not the same, sometimes off by a degree, or so.

So, not sure how to handle this.

Ideas, anyone?

Thanks
Dave

Idea:
According to my GPS manual there is not an option to not send magnetic variation. It's "Auto", "Grid" or "user setting" I'm not sure of the "Grid" I'll check. But it could be that Garmin didn't expect its gadget to still be working after the table is gone out!!??
But... maybe I'm not the only sailor having dated equipment. Could it be an idea to have the OCPN option to not trust the GPS but WMM instead??
The other idea is of course that I enter the variation value into the GPS after having read WMM?

[Neptune's Gear]

OK, here is some more data;

Below is a VDR file so you can see the data coming in;

$GPRMC,025248,A,3636.974,S,17447.296,E,0.0,128,160 214,19,E*57
$IIDE,1824,0,E,1.0$*59
$IIMWV,8.8,R,1.2,N,A*3E
$AHj c&
$GPGLL,3636.974,S,17447.296,E
$GPGGA,025249,3636.974,S,17447.296,E,1,5,3.0,16,M, 32,M
$GPVTG,,T,82,M,0.0,N,0.0,K
$GPZDA,025249,16,02,2014,-13
$IIHDG,1 2&4,0,E,1.0,E*59
$IIDPT,2.6,-0.3,100.0*69
$GPRMC,025249,A,3636.974,S,17447.296,E,0.0,101,160 214,19,E*5D
$IIMTW,37.4,C*13
$GPRMC,025248.00,A,3636.97181,S,17447.29617,E,0.07 7,,160214,,,D*6D
$II@$GPGLL,3636.974,S,17447.296,E
$GPGGA,025250,3636.974,S,17447.296,E,1,5,3.0,16,M, 32,M
$GPVTG,,T,52,M,0.0,N,0.0,K
$GPZDA,025250,16,02,2014,-13
$IIMTW,37.4,C*13
$GPRMC,025250,A,3636.974,S,17447.296,E,0.0,71,1602 14,19,E*63
$IIMWV,60.1,T,1.3,N,A*0E
$IIDBT,8.6,f,2.6,M,1.4,F*1E
$GPRMC,025251.00,A,3636.97178,S,17447.29619,E,0.06 6,,160214,,,D*6D
$GPGLL,3636.974,S,17447.296,E
$GPGGA,025251,3636.974,S,17447.296,E,1,5,3.0,16,M, 32,M
$GPVTG,,T,20,M,0.0,N,0.0,K
$IIHDG,182. ,,,1.,E*
$GPZDA,025251,16,02,2014,-13
$GPRMC,025251,A,3636.974,S,17447.296,E,0.0,39,1602 14,19,E*6E
$IIRSA,2.0,A,,*2D
$IIDBT,8.6,f,2.6,M,1.4,F*1E
$IIVLW,3856.262,N,1666.114,N*40
$IIVHW,,T,182.5,,0"0$N,0.,K*15
$GPGLL,3636.974,S,17447.296,E
$GPGGA,025252,3636.974,S,17447.296,E,1,5,3.0,16,M, 32,M
$GPRMC,025252.00,A,3636.97178,S,17447.29620,E,0.03 4,,160214,,,D*63
$GPVTG,,T,14,M,0.0,N,0.0,K
$GPZDA,025252,16,02,2014,-13
$GPRMC,025252,A,3636.974,S,17447.296,E,0.0,33,1602 14,19,E*67
$IIDBT,8.6,f,2.6,M,1.4,F*1E
$IIVLW,3856.262,N,1666.114,N*40
$IIVHW,,T,182.5,M,0.0,N,0.0,K*75
$GPGSA,A,3,42,02,50,04,17,24,10,12,20,,,,1.99,0.96 ,1.74*0B
$IIHDG,182.5,0E,1.0,E*5
$GPGLL,3636.974,S,17447.296,E
$IIDP,2.,-.3,10
$GPGGA,025253,3636.974,S,17447.296,E,1,5,3.0,16,M, 32,M
$GPVTG,,T,8,M,0.0,N,0.0,K
IIMUV,1(2.4,T,.,N,A*3D
$GPZDA,025253,16,02,2014,-13
$GPRMC,025253,A,3636.974,S,17447.296,E,0.0,27,1602 14,19,E*63
$GPRMC,025253.00,A,3636.97177,S,17447.29620,E,0.03 2,,160214,,,D*6B
$IIVHW,,T,182.5,M,0.0,N,0.0,K*75
$IIHDG,182.5,0,E,1.0,E*58
$IIDPT,2.6,-0.1,100.0*9
$GPGLL,3636.974,S,17447.296,E
$GPGGA,025254,3636.974,S,17447.296,E,1,5,3.0,16,M, 32,M
$GPVTG,,T,6,M,0.0,N,0.0,K
$GPZDA,025254,16,02,2014,-13
$GPRMC,025254,A,3636.974,S,17447.296,E,0.0,25,1602 14,19,E*66
$IIVHW,,T,182.6,M,0.0,N,0.0,K*76
!AIVDO,1,1,,B,C7`B5t@00;81p0rhi<`000N0Ve0CWI3M90aC K:000000B0h0PQPP,0*32
$IIHDG,182.6,0,E,1.0,E*5B
$GPRMC,025254.00,A,3636.97175,S,17447.29619,E,0.02 4,,160214,,,D*63
$GPGGA,025254.00,3636.97175,S,17447.29619,E,2,09,0 .96,14.0,M,28.7,M,,0000*71
$GPGLL,3636.974,S,17447.296,E
$GPGGA,025255,3636.974,S,17447.296,E,1,5,3.0,16,M, 32,M
$GPVTG,,T,333,M,0.0,N,0.0,K
$GPZDA,025255,16,02,2014,-13
$GPRMC,025255,A,3636.974,S,17447.296,E,0.0,352,160 214,19,E*54
$IIHDG,182.6,0,E,1.0,E*5B
$IIDPT,2.6,-0.3,100.0*69
$IIMTW,37.6,C*11
$IIMWV,204.2,T,2.8,B,A*35
$GPGLL,3636.974,S,17447.296,E
$GPRMC,025255.00,A,3636.97174,S,17447.29618,E,0.00 1,,160214,,,D*65
$GPGGA,025256,3636.974,S,17447.296,E,1,5,3.0,16,M, 32,M
$GPVTG,,T,316,M,0.0,N,0.0,K
$GPZDA,025256,16,02,2014,-13
$GPRMC,025256,A,3636.974,S,17447.296,E,0.0,335,160 214,19,E*56
$IIVHW,,T,182.7,M,008c Svv
$IIMTW,37.6,C*11
$IIMWV,211.1,T,3.7,N,A*3C
$GPGLL,3636.973,S,17447.296,E
$GPGGA,025257,3636.973,S,17447.296,E,1,5,3.0,16,M, 32,M
$GPVTG,,T,327,M,0.0,N,0.1,K
$GPZDA,025257,16,02,2014,-13
$GPRMC,025257.00,A,3636.97172,S,17447.29616,E,0.01 4,,160214,,,D*6B
$GPRMC,025257,A,3636.973,S,17447.296,E,0.0,346,160 214,19,E*54
$IIVHW$,T1 .7M,0 ,,0 K*7
$IIMWV,216.4,T,4.5,N,A*3B
$IIMWV,206.6,R,5.9,N,A*33
$IIRSA,2.0,A,,*2$GPGLL,3636.973,S,17447.296,E
$GPGGA,025258,3636.973,S,17447.296,E,1,5,3.0,16,M, 32,M
$GPVTG,,T,339,M,0.0,N,0.0,K
$GPZDA,025258,16,02,2014,-13
$IIVHW,,T,182.7,M, .0$GPGSA,A,3,42,02,50,04,17,24,10,12,20,,,,1.99,0. 96,1.74*0B
$GPRMC,025258,A,3636.973,S,17447.296,E,0.0,358,160 214,19,E*54
$IIDPT,2.6,-0.3,100.0*69
$IIMWV,200.6,R,5.3,N,A*3F
$IIRSA,2.0,A,,*2D
$IIDP,.6,f,2. ,M,1.4,F*1E
$GPGLL,3636.973,S,17447.296,E
$GPGGA,025259,3636.973,S,17447.296,E,1,5,3.0,16,M, 32,M
$GPVTG,,T,351,M,0.0,N,0.0,K
$GPZDA,025259,16,02,2014,-13
$IIHDG,182.7,0,E,1.0,E*A
$IIDPT, .6,- .3,100.0*69
$IIMTW,37.5,C*12
$GPRMC,025259,A,3636.973,S,17447.296,E,0.0,10,1602 14,19,E*6A
$IIRSA,2.0,A,,*2D
$IIDBT,8.6,f,2.6,M,1.4,F*1E
$GPRMC,025258.00,A,3636.97170,S,17447.29614,E,0.01 9,,160214,,,D*69
$GPGLL,3636.973,S,17447.296,E
$GPGGA,025300,3636.973,S,17447.296,E,1,5,3.0,16,M, 32,M
$GPVTG,,T,0,M,0.0,N,0.0,K
$GPZDA,025300,16,02,2014,-13
$GPRMC,025300,A,3636.973,S,17447.296,E,0.0,19,1602 14,19,E*6E
$IIDBT,8.6,f,2.6,M,1.4,F*1E
$IIVLW,3856.262,N,1666.114,N*40
$IIVHW,$T,18 .6,M,0.0,N,0.,K*76
$GPGLL,3636.973,S,17447.296,E
$GPGGA,025301,3636.973,S,17447.296,E,1,5,3.0,16,M, 32,M
$GPVTG,,T,3,M,0.0,N,0.0,K
$GPZDA,025301,16,02,2014,-13
$IIMWV,217.4,R,6.9,N,A*32
$GPRMC,025301,A,3636.973,S,17447.296,E,0.0,22,1602 14,19,E*67
$IIRSA, *0,A2D
$IIVLW,3856.262,N,1666.114,N*40
$IIVHW,,T,182.6,M,0.0,N,0.0,K*76
$GPGLL,3636.973,S,17447.296,E
$GPGSV,3,1,09,02,45,308,46,04,82,143,48,10,34,037, 49,12,27,223,43*71
$GPGSV,3,2,09,17,45,116,45,20,10,138,35,24,31,274, 43,42,34,310,42*79
$GPGSV,3,3,09,50,37,316,48*49
$AITMP,+38,0*51
!AIVDO,1,1,,B,H7`B5tA=J0W>j6rB1BVnD000000,2*35
!AIVDO,1,1,,B,H7`B5tDT0000000J=F00001P1130,0*48
$GPGGA,025302,3636.973,S,17447.296,E,1,5,3.0,16,M, 32,M
$GPVTG,,T,8,M,0.0,N,0.0,K
$GPZDA,025302,16,02,2014,-13
$IIRSA,2.0,A,,*2D
$GPRMC,025302.00,A,3636.97163,S,17447.29603,E,0.03 1,,160214,,,D*69
$GPRMC,025302,A,3636.973,S,17447.296,E,0.0,27,1602 14,19,E*61
!AIVDM,1,1,,A,H7`B5OlTCBD5pVTJ=jknn00h7040,0*26
$IIHDG,182.7,0,E,1.0,E*5A
$IIDPT,2.6,-0.3,100*0*29
$GPGLL,3636.973,S,17447.296,E
$GPGGA,025303,3636.973,S,17447.296,E,1,5,3.0,17,M, 32,M
$GPVTG,,T,0,M,0.0,N,0.0,K
$GPZDA,025303,16,02,2014,-13
$IIDBT,8.5,f,2.6,M,1.4,F*1D
$GPRMC,025303,A,3636.973,S,17447.296,E,0.0,19,1602 14,19,E*6D
$GPRMC,025303.00,A,3636.97163,S,17447.29602,E,0.00 7,,160214,,,D*6C
$GPGLL,3636.973,S,17447.296,E
$GPGGA,025304,3636.973,S,17447.296,E,1,5,3.0,17,M, 32,M
$GPVTG,,T,9,M,0.0,N,0.0,K
$GPZDA,025304,16,02,2014,-13
$IIVLW,3856.262,N,1666.114,N*40
$GPRMC,025304,A,3636.973,S,17447.296,E,0.0,28,1602 14,19,E*68
$IIVHW,,T,182.6,M,0.0,N,.$IIMTW,37.6,C*11
$IIMW, 13.3,T,6.5,N,A*3B
$GPRMC,025304.00,A,3636.97163,S,17447.29601,E,0.05 2,,160214,,,D*68
!AIVDM,1,1,,A,B7`B4t@0;S81oerhd6pFSwR5kP06,0*2A
$GPGLL,3636.973,S,17447.296,E
$GPGGA,025305,3636.973,S,17447.296,E,1,5,3.0,17,M, 32,M
$GPVTG,,T,22,M,0.0,N,0.0,K
$GPZDA,025305,16,02,2014,-13
$GPRMC,025305,A,3636.973,S,17447.296,E,0.0,41,1602 14,19,E*66
$IIVLW,3856.22N,1666.114,N4
$IIDPT,2.6,-0.3,100.0*69
$IIMTW,37.7,C*10
$IIMWV,206.3,T,6.6,N,A*3C
$IIMWV,18",R6.4,,A*32
$IIRS,2.0$,,*2D
$GPGLL,3636.973,S,17447.296,E
$GPGGA,025306,3636.973,S,17447.296,E,1,5,3.0,17,M, 32,M
$GPRMC,025306.00,A,3636.97163,S,17447.29599,E,0.00 7,,160214,,,D*68
$GPVTG,,T,27,M,0.0,N,0.0,K
$GPZDA,025306,16,02,2014,-13
$GPRMC,025306,A,3636.973,S,17447.296,E,0.0,46,1602 14,19,E*62
$IIMTW,37.6,C*11
$IIMWV,193.2,T,6.4,N,A*30
$IIMWV,184.7,R,5.9,N,A*3B
$IIRSA$2&0,A,,*D
$GPGLL,3636.973,S,17447.296,E
$GPGGA,025307,3636.973,S,17447.296,E,1,5,3.0,17,M, 32,M
$GPVTG,,T,21,M,0.0,N,0.0,K
$IIVL,3856*2 2fff F40
$IIVHW,,T,82.5,M,0.0,F0&0,K*75
$GPZDA,025307,16,02,2014,-13
$GPRMC,025307,A,3636.973,S,17447.296,E,0.0,40,1602 14,19,E*65
$GPRMC,025307.00,A,3636.97161,S,17447.29598,E,0.01 6,,160214,,,D*6A
$IIRSA,2.0,A,,*2D
$IIDBT,8.5,f,2.6,M,1.4,F*1D
$GPGLL,3636.973,S,17447.296,E
$GPGGA,025308,3636.973,S,17447.296,E,1,5,3.0,17,M, 32,M
$GPVTG,,T,4,M,0.0,N,0.0,K
$GPZDA,025308,16,02,2014,-13
$IIMWV,181.9,T,6.1,N,A*3D
$GPRMC,025308,A,3636.973,S,17447.296,E,0.0,23,1602 14,19,E*6F
$GPRMC,025308.00,A,3636.97160,S,17447.29596,E,0.03 2,,160214,,,D*6C
$IIDBT,8.6,f,2.6,M,1.4FE
$GPGLL,3636.973,S,17447.296,E
$GPGGA,025309,3636.973,S,17447.296,E,1,5,3.0,17,M, 32,M
$GPGGA,025308.00,3636.97160,S,17447.29596,E,2,09,0 .96,14.6,M,28.7,M,,0000*7F
$GPVTG,,T,345,M,0.0,N,0.0,K
$GPZDA,025309,16,02,2014,-13
$GPRMC,025309,A,3636.973,S,17447.296,E,0.0,4,16021 4,19,E*5B
$GPGSA,A,3,42,02,50,04,17,24,10,12,20,,,,1.99,0.96 ,1.74*0B
$IIRSA,2.0,A,,*2D
$IIDBT,8.6,f,2.6,M,1.4,F*1E
$IIVLW,3856.262,N,1666.114,N*40
$GPGLL,3636.973,S,17447.296,E
$GPGGA,025310,3636.973,S,17447.296,E,1,5,3.0,17,M, 32,M
$GPVTG,,T,335,M,0.0,N,0.1,K
$GPZDA,025310,16,02,2014,-13
$GPRMC,025310,A,3636.973,S,17447.296,E,0.0,354,160 214,19,E*55
$IIVLW,3856.262,N,1666.114,N*40
$IIVHW,,T,182.1,M,0.0,N,0.0,K*71
$IIHDG,18 c SV
$GPGLL,3636.973,S,17447.296,E
$GPRMC,025310.00,A,3636.97158,S,17447.29591,E,0.01 5,,160214,,,D*6C
$GPGGA,025311,3636.973,S,17447.296,E,1,5,3.0,17,M, 32,M
$GPVTG,,T,328,M,0.0,N,0.1,K
$GPZDA,025311,16,02,2014,-13
$IIMWV,179.,R,. ,N,A*34
$GPRMC,025311,A,3636.973,S,17447.296,E,0.0,347,160 214,19,E*56
$IIRSA,2.0,A,,*2D
$IIVHW,,T,181.9,M,0.0,N,0.0,K*7A
$IIHDG,181.9,0,E,1.0,E*57


Seems there is some corruption. I guess I'll have to go through all the connections again....

Any suggestions?

Matt

[bdbcat]

Hakan....

OK, one more try.
There was some trouble with priority handling, Also, the AIVDO sentence was (correctly) sending true heading as (NaN), since the transponder seems to have no idea of variation or heading. This was complicating the works even more.

All fixed now, I think.
Except for Checksum errors, the latest VDR file you sent now shows HDT in the dashboard, getting Var from WMM. Or at least it does for me

btw, NaN is a value we use to signify that the parameter does not exist. This is different from "equal to 0.0".

Dave

[bdbcat]

NeptunesGear...

Matt, you have some data corruption.
However, there is enough data to see th following trouble in the datastream.

You have two conflicting sources of Magnetic Variation.

$IIHDG,182.5,0E,1.0,E*5
This says Var = 1.0 E (clearly wrong for PNW)


$GPRMC,025248,A,3636.974,S,17447.296,E,0.0,128,160 214,19,E*57
This says Var = 19 E (better)

I guess that IIHDG is coming from your autopilot. Maybe it can be configured to not send VAR, or at least send a constant 19E value.

Good Luck
Dave

[Neptune's Gear]

Another set of eyes is a good thing!! Thanks, I'll look into that...
Cheers
Matt

[Hakan]

Originally Posted by bdbcat

Hakan....

OK, one more try.
There was some trouble with priority handling, Also, the AIVDO sentence was (correctly) sending true heading as (NaN), since the transponder seems to have no idea of variation or heading. This was complicating the works even more.

Thanks - so nice. You're a rock. Yes - I was trying to follow the priority logic as well but failed. Very good.

All fixed now, I think.
Except for Checksum errors, the latest VDR file you sent now shows HDT in the dashboard, getting Var from WMM. Or at least it does for me

I've tested in the boat and now the true mag is nicely shown and following the variation I send.
But I havn't had the opprtunity to test the switch to wmm data in real. That's becouse I can't get either the GPS nor the Simrad to send NAN instead of 0.0. My Simrad is by the way a bit silly. It seems to store the last received Var value in a register. So even if I switch the GPS off Simrad continue to send the last received value. Even if I switch also that off and on!

btw, NaN is a value we use to signify that the parameter does not exist. This is different from "equal to 0.0".

Thanks - I know NaN. The question was something else - but nerver mind - not important.


A possible discussion:
I still have the problem that my dated equipment don't know a correct variation. But they can be forced to send 0.0 instead of NaN. Well if I use the Garmin option "Automatic variation" it sends 0.2 but in manually mode I can force it to send 0.0. (Can that 0.2 be a Garmin internal logic to separate from 0.0? In that case Garmin equals 0.0 and NaN??)
So for my personal use I would like to have OCPN to correct this. I can see two possibilities:
1. If NMEA_ Var = "0.0" and wmm_Var > +-2 then use wmm_Var.
2. A user option > Use GPS(NMEA) variation | Use WMM variation.

I do understand your point from before that OCPN should not generally switch to wmm if the NMEA value is 0.0. There are positions on earth without variation. (Even if the value 0.0 would be rare and even never sent from a Garmin in automatic mode?) But I think I can understand and handle that situation. So if you have the time and the mind for it. Any advices for the best way to do alternative 1 would be much appreciated. But I'll start to have look myself.

Thanks Håkan