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Old 10-07-2019, 09:42   #1
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COG vs Heading in OpenCPN 5.0

Hi,

I am not sure to post at the right place ...if so, don't hesitate to move the message.
I am discovering OpenCPN and very pleased with what I could use up to now.
I did not test the earlier versions ... I am with 5.0.

It seems to me that COG and heading are reversed on the graphical interface.
This issue may have been discussed already ... I could not find anything about it !
Many thanks for your help.
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Old 10-07-2019, 09:49   #2
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Re: COG vs Heading in OpenCPN 5.0

Welcome aboard...


More detail on your COG and heading observation?
Screenshots help a lot.


Thanks
Dave
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Old 10-07-2019, 10:04   #3
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Re: COG vs Heading in OpenCPN 5.0

Thanks for your welcome !
In fact, what it is called COG should be named Heading and reverse.
It is particularly right when there is current. The two lines are well separated.
The boat (GPS / trace) is following the Heading line instead of the COG line ...
The length of these lines are configured in Options/Ships
Heading predictor - The one configured in NM
COG predictor - The one configured in "min"

The COG should be where you go, the heading is what you read ...

Hope to be clearer !
Cheers
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Old 10-07-2019, 10:37   #4
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Re: COG vs Heading in OpenCPN 5.0

Another image that may be more explicit ...
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Old 10-07-2019, 10:46   #5
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Re: COG vs Heading in OpenCPN 5.0

juancho38...


Sorry, not following.
COG is course over ground, in the picture the solid line with red square at end. This is where you will be in 5 minutes.
The dashed line coming from the bow of the boat is HDG, what would be read on a compass (with proper variation applied).
At this moment, the current clearly comes from the left, setting the ship to the east.


Am I missing something?


Dave
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Old 10-07-2019, 11:44   #6
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Re: COG vs Heading in OpenCPN 5.0

This is exactly what I expected ...
But as you can see on the 2nd picture, the boat (trace from GPS behind) is following 346.
346 in OpenCPN is the heading instead of being the COG.
I am using a NMEA simulator to get use to OCPN. Would it come from there ?
I may have miss something myself ...
Would you have a advise for another NMEA simulator, in case the GPS sentence follow the heading instead of the COG ....
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Old 10-07-2019, 14:00   #7
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Re: COG vs Heading in OpenCPN 5.0

Quote:
Originally Posted by juancho38 View Post
This is exactly what I expected ...
But as you can see on the 2nd picture, the boat (trace from GPS behind) is following 346.
346 in OpenCPN is the heading instead of being the COG.
I am using a NMEA simulator to get use to OCPN. Would it come from there ?
I may have miss something myself ...
Would you have a advise for another NMEA simulator, in case the GPS sentence follow the heading instead of the COG ....


Some simulators don’t apply the math behind the values to the position details and the COG heading etc don’t appear correct on any plotter.

I wrote a simulator in 1985 and I am working on one at the moment porting what I have learned, since ‘85 as far as extra features go. It is a long way off end user use

The simulator from 85 works correctly and the proof of concept work i have doesnt and that is because the math begind the POC has yet to be implemented.

OpenCPN does display COG and Heading correctly. That much I can say.

The free simulator chrome plugin has a few quirks and is one that doesn’t apply a set and drift value has no lag in the simulation to give some “realism” to the “headings” so the two lines from memory are always one and the same heading for example, the math on applied wind and GPS routines also has some particular GPS it is emulating and it isnt quite what usually is sent from most gps, however it is always being improved. And it is easy to operate. Might be worth a search for the now


There are a lot of windows based commercial simulators usually written in dotnet or visual basic available for a price. Most you can try for free they work for a while then stop.

I dont know how many would have background math most are really complex to configure and use so id imagine they do but configuring it isnt easy

ShipDriver is a beta plugin that Is available there are some suggestions I have put forward to Mike on the messaging and crc routines.

I am using this plugin to try and fast track developing a test tool. Both are still in development so the math isnt all implemented yet.

Ship driver will let you get an understanding of what opencpn will look like as is but it doesnt have all the message types to emulate a gps

it does look like an AIS equipped vessel. As I say works in progress. The code for reading the grib data and structure is very well thought out !

You cannot test the tactics plugin without enabling force TWD for example, more message type stuff.

Hope this helps


/Ron
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Old 10-07-2019, 15:44   #8
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Re: COG vs Heading in OpenCPN 5.0

Quote:
Originally Posted by juancho38 View Post
This is exactly what I expected ...
But as you can see on the 2nd picture, the boat (trace from GPS behind) is following 346.
346 in OpenCPN is the heading instead of being the COG.
I am using a NMEA simulator to get use to OCPN. Would it come from there ?
I may have miss something myself ...
Would you have a advise for another NMEA simulator, in case the GPS sentence follow the heading instead of the COG ....

I'll bet that the issue is with the NMEA sentences generated by the simulator, not OpenCPN.
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Old 10-07-2019, 16:00   #9
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Re: COG vs Heading in OpenCPN 5.0

Quote:
Originally Posted by juancho38 View Post
This is exactly what I expected ...
But as you can see on the 2nd picture, the boat (trace from GPS behind) is following 346.
346 in OpenCPN is the heading instead of being the COG.
I am using a NMEA simulator to get use to OCPN. Would it come from there ?
I may have miss something myself ...
Would you have a advise for another NMEA simulator, in case the GPS sentence follow the heading instead of the COG ....


The track behind is just the GPS fix points connected by straight line segments. That line has nothing to do with heading or COG.
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Old 10-07-2019, 16:52   #10
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Re: COG vs Heading in OpenCPN 5.0

Quote:
Originally Posted by juancho38 View Post
Would you have a advise for another NMEA simulator, in case the GPS sentence follow the heading instead of the COG ....
Maybe try the vdr with some sample data, Istr a file somewhere with heading as well as cog.
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Old 11-07-2019, 00:54   #11
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Re: COG vs Heading in OpenCPN 5.0

Thanks to all for your comments.
I can trust you that in real life COG is displayed "ad hoc" with a strong current.
I have not been navigating with strong currents using OpenCPN, most of the time, heading and COG are aligned, difference is negligible or... I pay more attention to the environment than the electronics !!

I suppose, the NMEA emulator GPS signal calculations follow HDT instead of COG even if it displays the correct COG calculation (various variables are showed in this emulator). That confused me ...

@transmitterdan : The track behind the boat must follow the COG (at least as close as, when correct) and not HDT. The boat is intended to go in the COG direction. In real life, I understand the trace is from GPS signal, it is always safe to cross check software calculations... What you see is what you get !

@RonSouthworth : I will give a try to ShipDriver and Google emulator, thanks !

Cheers !
JM.
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Old 11-07-2019, 07:19   #12
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Re: COG vs Heading in OpenCPN 5.0

One more question please.
I was trying to test tactics plugin displaying laylines, polars ... etc does not work. I suppose this is because it can not get STW.
So, I checked the Speed Through Water NMEA sentence (VWVHW) coming from the emulator.
My emulator sends the following sentence :
Code:
<GREEN>15:49:07 (Serial:COM30) $VWVHW,209.0,T,209.0,M,2.8,N,,5.3,K*74<0x0D><0x0A>
<BLUE>--> 15:49:07 (UDP:192.168.1.255:10110) $VWVHW,209.0,T,209.0,M,2.8,N,,5.3,K*74
as you can see, I forward the sentence to network (qtVlm plotting software).
I realized that OpenCPN "classic" dashboard does NOT read STW neither !

qtVlm DO read the STW forwarded by OCPN ... and it is different of COG (because of current) and coherent with the emulator values ...

Am I missing something again ? I feel lost !
Cheers.
JM.
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Old 11-07-2019, 18:51   #13
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Re: COG vs Heading in OpenCPN 5.0

Quote by juancho:

I was trying to test tactics plugin displaying laylines, polars ... etc does not work. I suppose this is because it can not get STW.

I believe this is a completely inaccurate statement, made because of presumption about the operation of tactics and misundwrstanding about its use.
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Old 11-07-2019, 18:55   #14
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Re: COG vs Heading in OpenCPN 5.0

Tactics is best used with STW data however there is an option for SOG. It is wrong to blame the software and misrepresent the facts when you haven't got your instrument data working properly yet. You can try using nmeaconverter to help with any conversion necessary.
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Old 11-07-2019, 23:12   #15
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Re: COG vs Heading in OpenCPN 5.0

Quote:
Originally Posted by rgleason View Post
Quote by juancho:

I was trying to test tactics plugin displaying laylines, polars ... etc does not work. I suppose this is because it can not get STW.

I believe this is a completely inaccurate statement, made because of presumption about the operation of tactics and misundwrstanding about its use.
Hi,

I am sorry to have miss typed my sentence, I didn't mean plugin is not working. Sorry again.
What I mean't is that I can not manage to have it working properly on my system, of course. I suppose it comes from the fact that STW is not decoded.

In my second post; I checked the VHW NMEA sentence, I do not understand why my system OPCPN is not decoding it ... while other systems do.

I considered NMEA converter, but I don't know what to change in the NMEA sentence for it to be decoded accordingly ...

Again, I did not want to hurt or anything like.

Cheers.
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