How is magnetic variation handled in FSX?

[Guest artmartin]

We've been having an active discussion in the Scenery Design Forum about this subject based on a problem I've had with one user of my scenery. He complained that, with my scenery installed, his magnetic heading all over the world is somehow improper. His example is at KSEA where on runway 34 his heading comes up at 0 instead of 340. Now I know for a fact that I've never done anything to magvar at any of the airports I've altered and, even if I did, one would think the problem would be completely local and not at some airport halfway around the world. Another forum post offered by a reader went into a fix someone found that was completely unrelated to any magvar setting in an AFCAD file. It turned out to be an unrelated corrupt .bgl file. All this brings up a major question. How is magnetic variation handled globally and locally in the present version and are there any changes planned in FSX that will preclude the problems we're seeing here? In FS9 there's a global magvar config file but each airport can have a magvar setting. Do those individual settings only affect the plane within the confines of the airport and the global setting takes over after that? There seems to be some confusion is the scenery design world over how this is handled and possibly a bug in the current version.Thanks,Art Martinnote: after posting this I read the post below about magdec.bgl. These posts are obviously related and maybe should be combined.

[Guest tdragger]

Magvar is handled on a global basis. We're going to try to update our magvar data to the recently published update.

[scott967 62]

I guess the question is that the magdec.bgl file format is undocumented in the SDKs, but appears to be unchanged from FS2000. It sounds like it will ccontinue to be used in FSX. The table format has been figured out, and in fact there have been replacement versions produced by 3rd parties.What seems less clear, is the realtionship of the global magdec to the magvar attributes that are assigned to airports, ILS, NDB, and VOR. Do these have to agree with the global magdec, or is the intent to provide local override (or maybe better resolution than is available in the global table).Uncertainty in this area makes it difficult to resolve problems with symptoms of "bad compass heading reading" or "bad VOR or more commonly ILS heading". The thing I suspect is that the change in Airport Facility Data handling in FS9 maybe introduced some of these apparent issues. FS9 went a long ways towards integrating airport scenery into the overall scenery. It would be nice to see this continue in FSX. For example, if the airport scenery could be positioned at ground level, rather than having an explicit elevation assigned to it. I can see the reason for doing it the way it's done in FS9 (you don't need to compute any mesh model to determine data that might be needed for the map or GPS).scott s..

[mgh 89]

Does that mean that the magnetic variation values listed for Airports, ILS(GP), Waypoints, NDBs, and VORS in the SDK aren't used in Flight Simulator?

[Guest tdragger]

Only in the map. They have no effect on the sim.

[Guest steve_j]

Hi!How about the NGA World Magnetic Model (http://www.ngdc.noaa.gov/seg/WMM/)? Is this used for the global coverage?regards,Stephan