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Old 27-07-2018, 04:15   #1
LJK
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Own ship icon oriented to COG not HDG

Dear All,

I have an interesting issue to do with the display of Mag HDG versus COG in OpenCPN 4.8.4 running on a Windows 7 PC.

NMEA stream from an OpenPlotter multiplexer contains VHW and HDM as well as COG.

The dashboard displays that data, so OpenCPN has it (see screenshot).

However the own ship icon is oriented to COG and no MAG heading is displayed. Own ship points stubbornly in the direction of COG, not over the bow! (See screenshot showing dashboard and my own ship pointed in the wrong direction.)

The issue seems related to the bug mentioned here:

No HDG Data Display In OpenCPN

But I would have expected it to be long resolved?

Any tips gratefully received.

thanks,

Lance
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Old 27-07-2018, 06:56   #2
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Re: Own ship icon oriented to COG not HDG

ensure wmm plugin is enabled
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Old 27-07-2018, 18:00   #3
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Re: Own ship icon oriented to COG not HDG

To amplify...

It makes no sense to use mag heading for any rendering on a true north Mercator projection chart.

The ownship rendering to true heading, and heading predictor vector, are displayed only if a true heading value is available.

If HDT is not actually present in any NMEA message, we use HDM and variation (typically from WMM plugin) to estimate an effective HDT.

So, enable the WMM plugin, and all will be well.

Dave
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Old 02-08-2018, 21:41   #4
LJK
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Re: Own ship icon oriented to COG not HDG

Thank you both for your help; for the instant fix (the WMM plugin was indeed not enabled) and the cogent explanation of why it is needed. I thought HDM was sufficient and now understand why not.
with thanks,
Lance
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Old 04-08-2018, 19:29   #5
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Re: Own ship icon oriented to COG not HDG

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