I am not seeing True Wind Angle and Speed on OpenCPN

[J.Hernandez]

Forgive my lack of knowledge.

My OpenCPN dashboard is not displaying True Wind direction or angle.
My goal is to get this data recorded using the VDR plugin so I can analyze later.

I get my STW data from a NMEA0183 sensor patched in to a NMEA 2000 network which is the backbone of the boat's electronics. The wind data is already native NMEA 2000 and these are forwarded to the Raymarine display in the cockpit that calculates and displays correctly True and Apparent wind speed and angle. But this is not the case for the dashboard in OpenCPN. I can't see True wind here. Only Apparent wind.



I am able to receive data from my NMEA 2000 network into a Raspberry Pi 4 running OpenCPN and Signal K via an Actisense NGT-1. I have a Network connection on port 3000 in OpenCPN to receive the Signal K data. I have a Signal K plugin called Signal K to NMEA0183 enabled to convert all the Signal K data to NMEA0183 so that the VDR plugin can read it. I believe I have checked the proper PGNs in the ACtisense and sentences in the SK to N0183 plugin to be passed to OpenCPN. I have a working UDP connection between Signal K and OpenCPN to send the NMEA0183 data.


This is a sample of a VDR recorded file with the data that is currently being received:

$IIMWV,138.97,R,3.29,M,A*32
$IIVWR,138.97,R,6.40,N,3.29,M,11.84,K*7B
$IIMWV,121.47,R,3.29,M,A*37
$IIVWR,121.47,R,6.40,N,3.29,M,11.84,K*7E
$IIMTW,14.6,C*10
$IIMWV,121.47,R,3.29,M,A*37
$IIVWR,121.47,R,6.40,N,3.29,M,11.84,K*7E
$IIMWV,121.47,R,3.29,M,A*37
$IIVWR,121.47,R,6.40,N,3.29,M,11.84,K*7E
$IIMWV,121.47,R,3.29,M,A*37
$IIVWR,121.47,R,6.40,N,3.29,M,11.84,K*7E
$IIMWV,121.47,R,3.29,M,A*37
$IIVWR,121.47,R,6.40,N,3.29,M,11.84,K*7E
$IIDBT,81.8,f,24.94,M,13.6,F*1F
$IIMWV,121.47,R,3.29,M,A*37
$IIVWR,121.47,R,6.40,N,3.29,M,11.84,K*7E
$IIMTW,14.6,C*10

I can't find any MWD or VHW or VWT sentences.

Any help would be appreciated.

[rooiedirk]

Dashboard is only showing data. Data that is not coming in, can't be shown.

If you are ready to do a deep dive in nmea you might install the nmea-converter plugin and calculate your own sentences. Altough you would need also a heading and speed input.

[J.Hernandez]

I am willing to.

The boat gets heading via GPS and speed data from a transducer. I am not sure I am routing that info correctly.

[Corsair63]

To get the true speed and direction of the wind you have to have the input of the true course and speed.
of course, as per roojerdik says you can do the calculation using the COG and speed from GNSS, but you have to use nmea-converter plugin, the help in the web about this plugin is useful and I guess that in the same help comes an example of converting the app wind into true wind.

if you could do the calculation, you'll be able to have the NMEA string available in VDR recording plugin.

[CrispyCringle]

True wind direction and speed is derived from a couple of inputs. I havnt thought about it in awhile, but I think it needs GPS speed (ground speed), apparent speed (water wheel speed), and AWA and speed. You may be missing one of those.

I apologize because I know I mix aviation terms with nautical. My history.

[J.Hernandez]

I installed the Derived Data plugin and I am seeing True Wind data in the Data browser in Signal K but these data is not passing to OpenCPN despite having both the SignalK 3000 network connection and the Signal K to NMEA 0183 plugin working.

What am I missing?

[Hakan]

To calculate a valid true wind angle, by OCPN or other apps, a heading input is needed as of Corsair's post. If only magnetic heading is available plugin WMM will make it true.

Using COG for true wind calculation will not make a usable true wind due to leeway or similar.

[J.Hernandez]

Originally Posted by Hakan

To calculate a valid true wind angle, by OCPN or other apps, a heading input is needed as of Corsair's post. If only magnetic heading is available plugin WMM will make it true.

Using COG for true wind calculation will not make a usable true wind due to leeway or similar.

I already have the WMM plaugin installed and enabled. That does not seem to be the problem.

Like I said, using the SK plagin Derived Data I am able to see the calculated True wind speed and direction when I look at the Data Browser like this:



Both TRUE and APPARENT are equal now because the boat is moored. The problem seems to be that these Derived Data is not being send to OpenCPN from SK either as SK data or N0183 data.

[Hakan]

We don't know how this true angle is derived if no heading is available, but anyhow..
To let Dashboard use the "environment.wind.angleTrueGround", instead of "environment.wind.angleTrueWater" you need to tell Dashboard to do so:
Dashboard (right click) Preferences.. -> Appearance: Select: [] Use N2k_SignalK true wind data over ground.

[Hakan]

btw:
Some legends for OCPN:
Wind direction is the angle related to north. (Meteorologic)
Wind angle is the angle related to ship's bow. (Used for sailing)

[J.Hernandez]

I seem to be getting somewhere.



I abandoned the SK plugin Derived data because it took me nowhere. I switched to the OpenCPN plugin NMEA Converter. There I used this sentence:

$XXMWV,90-deg(atan(($??MWV3*cos(rad($??MWV1))-$GPRMC7)/$??MWV3*sin(rad($??MWV1)))),T,sqrt(sqr($??MWV3*sin (rad($??MWV1)))+sqr($??MWV3*cos(rad($??MWV1))-$GPRMC7)),N,A

Which I modified to:

$XXMWV,90-deg(atan(($IIMWV3*cos(rad($IIMWV1))-$GNRMC7)/$IIMWV3*sin(rad($IIMWV1)))),T,sqrt(sqr($IIMWV3*sin (rad($IIMWV1)))+sqr($IIMWV3*cos(rad($IIMWV1))-$GNRMC7)),N,A

in order to suit my system/data better but it's esentially the same. Now I get TRUE WIND data!!

There's one thing I don't like about the formula used. It is based on SOG instead of STW. I do have the STW reading in my system (currently 0.0 because the boat is moored) but I reviewed a previous recording of NMEA0183 data and I can't find the sentence VHM there. I can see the PGN 128259 coming into SK from my Raymarine network and I have the SK plugin "SK to NMEA0183" enabled and VHM checked but it's not appearing in the NMEA debug window in OpenCPN. Am I missing something? I would prefer to use VHM (STW) over SOG for the calculation.

[Hakan]

VHM?? - Maybe turn the last letter upside down?
Spec for VHW is here.

[J.Hernandez]

Oops! Yes. I meant VHW. Working up too late.

As I was saying I would like to use $??VHW5 in the formula. That value represents STW in knots.

I am getting that info from my NMEA2000 network and SK can see it as you can see here as PGN 128259.



And I am sending that over UDP2000 to OpenCPN after converting the SK data to NMEA0183 as you can see here:



And I do see in the OpenCPN dashboard so I must be getting that sentence trough:



But it is NOT appearing in the NMEA debug windows or in the VDR recorded files which where I needed it to be in order to use it, correct?:

[barcoMeCasa]

Derived data works fine for me, but why are you using UDP to get data from signalk into opencpn? Signalk by default sends out nmea0183 on TCP port 10110, that's what most people use. On my setup derived data creates the true wind sigK delkta then signalk to nmea sends it out over tpc port 10110.

SigK questions might be better asked direct to the sigK team > https://discord.gg/vzRREWBn

[nohal]

Because UDP is a much better protocol for this kind of application. People use TCP because of lack of knowledge, hardware limitations or combination of both, but there is no real reason to do it and their life would be better with UDP in the majority of cases.

If Signal K server sends different NMEA 0183 data over TCP and UDP, then it is a bug in that server.

The real question here of course is why use NMEA 0183 at all here as it means double conversion of data.