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Old 09-02-2019, 06:17   #2296
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Re: Beta Test / Technical

Quote:
Originally Posted by nohal View Post
It is not possible. (What you posted is a simple typo, the real reasons are completely different, but it is not possible)
Again, you don't have to compile anything yourself - in fraction of the time you will burn on getting it done, every single plugin may have automatic builds on Appveyor running.

Yes, a typo. What a nice Nohal software machine that will be!
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Old 14-02-2019, 07:31   #2297
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Re: Beta Test / Technical

The OpenCPN RMB output statement shows incorrect data in field 12 after "Bearing to destination". This data is the VMG or effective speed towards the waypoint.
The version of OpenCPN is 4.8.4, and the data that appears Match with the SOG.
The correct information is the one that appears in the navigation window as VMG.
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Old 14-02-2019, 08:43   #2298
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Re: Beta Test / Technical

Tehani..
What I can found out in the present code for OpenCPN Ver 4.99.1408 Beta, is the ECRMB transmit to for example an Autopilot during Navigation an active route the speed value is the SOG received from a GPS. (Or any incoming data from somewhere that has the shape of GPS data.)

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Old 14-02-2019, 12:24   #2299
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Re: Beta Test / Technical

Hakan,
Please read the NMEA0183 document: "Standard For Interfacing Marine Electronic Devices", version 3.01 of January 1, 2002. Field 12: Destination closing velocity, knots.
I interpret that this data must be the approach speed to the waypoint, that is, the VMG.
Therefore, the correct data is the calculated VMG = SOG * cos (COG - BRG) and not the one generated directly by the GPS receiver device (SOG).
Obviosuly, the SOG data can be obtained from RMC and VTC.

Regards, Tehani.
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Old 14-02-2019, 12:32   #2300
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Re: Beta Test / Technical

Tehani,

in case you have the NMEA document at hand, please contact Håkan how to make the content accessible for him. It is not in public domain. NMEA docs are closed source.

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Old 14-02-2019, 17:53   #2301
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Re: Beta Test / Technical

The standard says “destination closing velocity knots”.
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Old 16-02-2019, 10:43   #2302
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Re: Beta Test / Technical

It would be "Destination closing velocity in knots" should be interpreted to something like WMG. I'm not the English native here.
Why OpenCPN code is printing SOG I don't know. Some historical knowledge that can bring light to this?
One history can be old APs don't use this data to anything so than SOG can be good enough? How a modern AP take care of this data I'm not aware of. If it's important it would not be a big effort to change I suppose.
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Old 16-02-2019, 11:02   #2303
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Re: Beta Test / Technical

Hakan,
It is true, VMG / VMC are not useful data for autopilots, but they are very useful for "human sailors", and therefore, it is necessary to send them correctly to be visualized in the instrumentation, or in the apps that receive that data.

The information that OpenCPN delivers can be forwarded to other wired buses (NMEA0183 / NMEA2000) through gateways.
It is better to leave the field as null, than to introduce an erroneous data, because this prevents the subsequent calculation.
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Old 16-02-2019, 11:15   #2304
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Re: Beta Test / Technical

Tehani...
I could be, but basically the output (EC)RMB from OpenCPN is meant for an AP and is only sent out while a route is activated for navigation.

If you need other data to any connected instruments or data bus the best would be to set up that output in the tools->connections dialog and select appropriate NMEA sentences to be forwarded by the inbound multiplexer.

But I may agree the ECRMB produced by OpenCPN would carry correct data according to the specification. So, again, anyone who knows the history for printing SOG instead of WMG are welcome to bring light to this.
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Old 16-02-2019, 17:26   #2305
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Beta Test / Technical

I will do some research to see if there is a historical reason. I see no reason to send SOG in a field meaning "closing speed". It is ok that RMB is only sent when running a route. That's the only time closing speed has a meaning.
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