Tactics Plugin

[tom_BigSpeedy]

Originally Posted by rgleason

Tom,
I have a question regarding calculation of True Wind while using COG/SOG data.
Isn't it necessary to modify the ground track (COG/SOG) with DRIFT (current + leeway) data to get the accurate True Wind Speed and Direction?

See Dashboard post/discussion here please. http://www.cruisersforum.com/forums/...ml#post2195920

Rick,
I've seen the discussion yesterday on the dashboard_pi plugin thread but had no time answer...
From my understanding, it makes sense to use SOG instead of STW as, like Fabbian said, the challenge is to merge 2 coordinate systems :
a) the earth coordinate system (true wind blowing over the water surface and boat moving over the surface with SOG / COG) and
b) the boat coordinate system (measurement of AWS /AWD based on the boat axis, this is what we see/read sitting on the boat without a GPS)

The link between both is, that we can measure SOG / COG with a GPS which is movement of the boat in b) in the a) system ...

But we have to take care, we cannot use COG directly, because your wind sensor is calibrated on the boat axis of system b) (and shows data based on HDG/HDT).
To get a precise result, we should correct this measurement then by set & drift (leeway), you're right.
Currently tactics_pi only corrects for leeway.
I'll be out sailing next two weeks , and will look into this.

Originally Posted by rgleason

Correction: Set & Drift are the compass direction and speed that water is moving.
Leeway is not a part of Set & Drift.

In the boat coordinate system a) we're moving with STW / HDT, i.e. we see speed and heading as STW and HDT (if we had no GPS on board).
Whereas someone from outside sees us moving on the earth surface in system b) with SOG / COG.

The difference between both vectors STW/HDT and SOG/COG is set & drift, with set = current and drift = leeway.

Does that clearify ? Or is it even more confusing now ?

Thomas

[tom_BigSpeedy]

Originally Posted by rgleason

Perhaps tom_bigspeedy can help explain the difference between VMG to wind and VMG to wpt. Maybe looking carefully at Tactics_pi User Manual and definitions will help. The diagrams are excellent. I intend to get some diagrams into OpenCpn Terminology page after I get Thomas's Tactics_pi user manual upload to the website.

Rick, Fabbian et all,

check these 2 pages out for the difference for 'VMG upwind' and 'VMG to waypoint' (which I call CMG and the author VMC):
https://76trombones.wordpress.com/20...-diagrams-vmg/
https://76trombones.wordpress.com/20...-diagrams-vmc/

And here are 2 practical examples for VMG / CMG from the same page and how you can manually do this with your polar file plot:

https://76trombones.wordpress.com/20...ing-in-shifts/
https://76trombones.wordpress.com/20...ing-in-shifts/


Thomas

[Neptune's Gear]

Tom, I have been using your tactics plugin for a while now, it's great. thx.
I have a question though. The Polar data can be displayed on the screen fine, but I'd like to be able to send out the polar target speed to be displayed on the instruments (NMEA2000). I've been thinking that this won't be strait forward as the PC "speaks" nmea0183 and there is no sentence for polar targets. There probably is a PGN for the NMEA2000 though.
Have you thought of this, is it possible, in a future version?
Thanks

[tom_BigSpeedy]

Originally Posted by Neptune's Gear

...
I've been thinking that this won't be strait forward as the PC "speaks" nmea0183 and there is no sentence for polar targets. There probably is a PGN for the NMEA2000 though.
Have you thought of this, is it possible, in a future version?
Thanks

Hi,
I'm using NKE and the NKE instrument bus uses 5 or 6 socalled Performance-Parameters, these are special, proprietary NMEA183 sentences ($PNKEP...).
Indeed I have already thought (! not programmed !) about sending e.g. current speed & direction or Target-VMG to my instruments.
This might be straight forward, I'd just need to define an outgoing NMEA queue, generate those sentences and put them into the NMEA queue.
We're already doing this with autopilot commands ...
BUT: this is existing NMEA183 ...

First of all, O would have to be enabled to read / send NMEA2000 records.
But that's not a matter of a plugin, but the system itself...
And I think this is gonna be quite a bit of a project ...

If that should be available one day, I'll probably aready have a solution available for NMEA183 sentence export, which I can extend to NMEA2000 PGNs then.

But good hint, in case I start working on the NMEA183 export, I'll make it flexible enough to adopt it later on to PGNs.

Best,

Thomas

[bcn]

Thomas,

in this context you might have a look at a feature request from today:
http://www.cruisersforum.com/forums/...ml#post2234915
Think it fits here as well

Hubert

[Neptune's Gear]

Thomas, if you can generate an nmea0183 sentence that's unique, we may be able to get the guys at actisense to convert it to nmea2000 for us. Could you provide me with a sample nmea0183 sentence? I'll give it to them and see what they say.
At this time my PC communicates from opencpn's NMEA 0183 system to my nmea2000 system (B&G) via an Actisense gateway.
Worth a try?


Sent from my iPad using Cruisers Sailing Forum

[tom_BigSpeedy]

Originally Posted by bcn

Thomas,

in this context you might have a look at a feature request from today:
http://www.cruisersforum.com/forums/...ml#post2234915
Think it fits here as well

Hubert

Hi Hubert,

that's the old philosophy question "do we want to manipulate incoming instrument data".
We had this discussion for various topics over years, like damping nervous GPS course and speed data, True Wind Speed calculation, damping noisy apparent wind data, etc.

It's the main reason why I did my own separate plugin instead of adopting dashboard_pi, because the clear answer always was : NO !

At some point I got annoyed and did the tactics_pi project, where I do manipulate and dampen data, do true wind calculation, do surface current caculation, etc.
But that's all captured inside the tactics_pi nutshell only.
I do neither export nor touch existing NMEA records in O itself for the reasons above.
It's a different story if I create a new, not yet exisiting NMEA record and share it on the bus versus overwriting existing data.
But George64 explicitly requests a manipultion of NMEA data in the O queue itself.
I recommend to raise this question in the O community, if we really want this.
And if that should ever happen, I'm happy to merge tactics_pi back into dashboard as well, which is still only a plugin, but the standard plugin for everyone :-)

Best,

Thomas

[transmitterdan]

Dashboard PI filtering does not affect any other plugin or NMEA output stream. If you think it does tell me where and I will look into it.

[tom_BigSpeedy]

Originally Posted by transmitterdan

Dashboard PI filtering does not affect any other plugin or NMEA output stream. If you think it does tell me where and I will look into it.

Dan,
no it doesn't, don't worry.
I know, because I merged your code in tactics_pi as well :-)

Thomas

[tom_BigSpeedy]

Originally Posted by Neptune's Gear

Thomas, if you can generate an nmea0183 sentence that's unique, we may be able to get the guys at actisense to convert it to nmea2000 for us. Could you provide me with a sample nmea0183 sentence? I'll give it to them and see what they say.
At this time my PC communicates from opencpn's NMEA 0183 system to my nmea2000 system (B&G) via an Actisense gateway.
Worth a try?


Sent from my iPad using Cruisers Sailing Forum

Yes, woth a try, but will take a bit to implement
Let's see if I can (manually) generate a NMEA sample over the weekend.

Would be a nice Arduino/PI project I guess :-)

I cannot fully work right now, I'm about to switching machines (laptops).
Thomas

[bcn]

Originally Posted by tom_BigSpeedy

Would be a nice Arduino/PI project I guess :-)

The next version of OpenPlotter will bring something in this direction if I'm informed correctly - or make it simple to add such a functionality.

For presenting data - the feature request - SignalK and its data server would be the candidate. Just using a browser to visualize data on different devices.
In this field some dust has to settle down (outside of OCPN) but then this would be a way.

[seandepagnier]

Originally Posted by tom_BigSpeedy

Hi,
I'm using NKE and the NKE instrument bus uses 5 or 6 socalled Performance-Parameters, these are special, proprietary NMEA183 sentences ($PNKEP...).

Any idea what these values represent?

[fallingeggs]

Originally Posted by Neptune's Gear

Thomas, if you can generate an nmea0183 sentence that's unique, we may be able to get the guys at actisense to convert it to nmea2000 for us. Could you provide me with a sample nmea0183 sentence? I'll give it to them and see what they say.
At this time my PC communicates from opencpn's NMEA 0183 system to my nmea2000 system (B&G) via an Actisense gateway.
Worth a try?


Sent from my iPad using Cruisers Sailing Forum

In my quest to pick which gear to install (going B&G), I asked myself the same question. I believe the problem is two fold.

First, there isn't a standard PNG for polar targets. Not a big issue as you can make a custom one or a custom 0183.

Second issue, and harder to overcome, is that B&G won't recognize or display custom PNGs. Folks at Sailing Anarchy, who seem to be a bit more race focused than us, blame this on B&G wanting to protect its high price H5000 system, which can display polar targets. (Bastards!)

On the other hand, Garmin, who has no fancy racing software, seems to be fine with displaying custom PNGs. Other displays from NKE and Android apps can as well. I've been thinking of going down the app route and using a temporarily mounted phone when I want the data. Sorry, don't remember the apps name off the top of my head, but it wasn't hard to find.

Will be happy to hear if you come up with a better solution. Installing the gear this winter.

[rgleason]

http://www.cruisersforum.com/forums/...ml#post2196617

The difference between both vectors STW/HDT and SOG/COG is set & drift, with set = current and drift = leeway.

Does that clearify ? Or is it even more confusing now ?

Thomas,
1. I understand the two frames of reference.

• Moving boat = Speed thru water / Heading
• Ground = Speed over ground / Course over ground

2. I understand the vector difference

• Is something important. But what is it?

STW/HDT is where the boat thinks its going and SOG/COG shows where on the ground it is actually going.
What causes the difference?
1. Water currents acting on the hull of the boat (tide, etc)
2. Waves beating on the hull in a certain direction.
3. Leeway due to sailing, which one of the resultant forces from the sail.
4. The force of wind on the hull?
5. Is the difference between being on the rocks or not.

So where do Set and Drift fit in?
Together they represent a vector force (direction and speed) of water that is moving?
Does leeway apply to the wind on the hull as well as sailing? - I say yes.
Where does waves beating on the hull go? Set & Drift?

Under Terminology

Set (SET) - Compass direction of moving water (In the direction of the moving water). This movement may be caused by a number of factors, including; tide, ocean currents, river flows etc.

Drift (DFT) – Speed that the water is moving. This movement may be caused by a number of factors, including; tide, ocean currents, river flows etc.

Leeway – Leeway is the angle between the HDG and the CRS and results from the lateral movement experienced by the boat as she moves forward through the water.. The empirical formula is that
Leeway = -1 * k * Heel / BSP^2. The formula itself is often called into question, especially with planning hulls. The k value, which is boat specific, will vary according to crew numbers and boat loading.

[rgleason]

I think of Set & Drift (due to moving water) AND Leeway (forces related to wind) as two different forces.