On 12/03/13 18:48, James Turner wrote:
On 12 Mar 2013, at 17:55, Stuart Buchanan <stuar...@gmail.com
<mailto:stuar...@gmail.com>> wrote:
Now the comments at the beginning of coremag.cxx imply that the module
originally implemented
wmm2000 and was updated by Wim Van Hoydonck
(wim.van.hoydo...@gmail.com <mailto:wim.van.hoydo...@gmail.com>) to
wmm2005.
The current version is now wmm2010, and I wonder if simgear has been
updated to reflect this?
Could this account for my heading discrepancy at EGPF?
Probably not. It's more likely that the magnetic variation has
simply changed
since the runway number was set, as it varies over time.
However, it probably wouldn't do any harm to update our model - the
model is supposed to model the physical earth, and navigation data /
charts *do* get out of sync Stuart with that - so as far as I can
see, updating to a more accurate model shouldn't break anything.
If you want to cook up a merge request, I'll apply it. We have time to
back it out if the universe explodes :)
James
Thank you Stuart & James for your responses,
Stuart, I was not so much interested in what is painted on the ground,
but what is indicated on the slaved
gyro. Your comments have made me reconsider my maths.
apt.dat shows a true heading for EGPF R05 of 46.34 (where does one find
true runway headings?)
Magvar on 2011 was 4.0W
(http://www.nats-uk.ead-it.com/public/index.php%3Foption=com_content&task=blogcategory&id=72&Itemid=121.html)
Annual Rate of Change 0.17°E (source as above)
So current Magvar =3.66W
Now I suppose I must ADD? this figure to the true heading? giving
50.00 as the magnetic heading for EGPF R05.
The slaved compass reports 50.03, which is good enough for me, But I
wonder if, as James suggested, upgrading to
ww2010 might lose the tiny difference. I may try this on a local repo
and see what happens.
Sorry for thinking aloud, but I find this wmm stuff fascinating, though
complicated.
Thanks
Alasdair
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