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Old 19-05-2015, 08:43   #1
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WMM : new model EMM

Hello

NOAA announced a new model more accurate.
Is there a way to use it in OpenCPN WMM plugin ?

Jean

Enhanced Magnetic Model: http://www.ngdc.noaa.gov/geomag/EMM/
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Old 19-05-2015, 09:01   #2
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Re: WMM : new model EMM

Jean...
Do you think it is worth the size (30MB for the computationally intensive / = very slow / version and 530MB for the precomputed one)?
As of now I don't think I'm going to implement it in the plugin, unless someone shows me some clear benefits for navigation doing so.

Pavel
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Old 19-05-2015, 10:16   #3
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Re: WMM : new model EMM

Pavel's view is totally accepted by me.
The example on NOAA's site shows a maximum variation divergence of 0.3 degrees from WMM at a single point. How can that bother our navigation in boats swinging 5 to 10 degrees? I can hardly keep a compass course within +-5 degrees!
Håkan
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Old 19-05-2015, 10:26   #4
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Re: WMM : new model EMM

OK OK ! you are probably right.
I did not think about the size of data to compute.

Jean
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Old 19-05-2015, 14:22   #5
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Re: WMM : new model EMM

Hello Pavel,

How much work is involved in adding the new version? I am using transits for adjusting magnetic compasses where I need an accuracy of 0.5 degrees. 0.3 degrees does make a difference for this application.

Ok, I modified the output of OpenCPN to show a bearing accuracy of 0.1 degrees for routes and the measuring tool.

Two versions? But if it is a lot of work I can use the NOAA online calculator for the limited number of locations I work from.

Mike
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Old 19-05-2015, 15:56   #6
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Re: WMM : new model EMM

Mike...
I did not even look at the code for EMM as soon as I spotted the size of the model, but suppose it will be similar to the WMM library bundled with the plugin now.
It should not be too hard to integrate it, but it definitely isn't a drop-in replacement. And the C code from NOAA sure needs some tweaking to compile inside the plugin as did the WMM lib.

Pavel
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Old 20-05-2015, 01:52   #7
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Re: WMM : new model EMM

Thanks Pavel,

Better to use the Online NOAA calculator for my situation I think.

Mike
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