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scott967

Magnetic variation problem

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I posted this on scenerydesign.org so please ignore it if you've responded on there. I just need more eyes looking at this one. Recently, a user of my photoreal scenery has complained to me that, with my scenery loaded, he gets errors in compass readings at airports far out of the Phoenix area such as KSEA. Logic would dictate that, even if I had magvar errors in one of the airport files for the Phoenix area, it would only show up locally. I've looked into the XML for all the AFCAD files I've distributed and the magvar settings seem reasonable and match the code in the original .bgl's that AFCAD extracted the info from. Has anyone else ever seen this problem and, if so, how does one go about tracking it down? Perhaps it's not even related to magvar airport settings. My scenery includes photoreal layers, flattens, GMAX objects, autogen, and some reworked airport files. I can't imagine how any of those other things could affect one's compass settings at distant airports. Art

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Hi Art,Sounds like something is overriding or disabling the magdec.bgl.(340 magnetic = approx. 000 true at KSEA)I encountered a problem like this with the Torres Straits scenery by Mal Lloyd (aerotropics.zip in the library). An exclude file (ydni_excl.bgl) wasn't properly compiled - it just contained some scasm(? I'm not an expert!) header information in text format. With this one particular file active, my heading indicator would show true heading instead of magnetic ALL OVER THE WORLD! With the file removed, everything was back to normal. There was nothing wrong with magdec.bgl, but something about the rogue file rendered it inoperable.Don't know if this will help you much, but perhaps it might give you an indication of what to look for. Even an exclude file could be the culprit.Regards,AdrianLGTSP.S. If I'm allowed to link to the other site's forum, see also:http://forums.flightsim.com/dc/dcboard.php...ing_type=search

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Boy, do I have a ton of exclude files in my scenery. I'll start renaming them one by one to see if it cures the problems. Big thanks.Art

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I think the particular file referenced was not a valid bgl file. Not sure how or why it would cause magdec to go haywire. I would have thought FS would either just ignore it or crash!I was interested in a different thread on magdec, so this got my interest. I d/led the problem sceenry and took a look at the bad file. This is what is in the "exclude" bgl:; YDNI_EXCL.BGL 30/06/2004 - 19:50:36 Version 1.0 Build 8 GENERAL-FILEFORMAT = 260125-ECHELLE = 1-AUTEUR = -RANGE = 30 KM-COMMENT1 = -BGLDIRECTORY = d:Program FilesMicrosoft GamesFS2004Addon Sceneryscenery FINWhich looks just like the format of an airport for windows .apt project file (with no actual scenery defined)!So, unless you think you have a bogus file in your distribution, I wouldn't spend too much time chasing this.But the bigger question: I have from time to time read reports of simmers having problems with their compass not reading correctly. I have never seen an exact cause of the problem -- just an attribution to "bad scenery" or "bad file".I am curious just what goes into the mag compass heading -- besides magdec.bgl obviously. In particular, what do all the various MAGVAR attributes that seem to be throughout the default AP files actually do?scott s..

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Good question Scott but you'd think that whatever affect they'd have would be completely local to that individual airport. Perhaps they mean that, if you sit on one of the runways of that particular airport, your magnetic variation is adjusted to that amount. Once you're out of range of that runway, it returns to the default. Seems a strange way of doing things but I guess it's in the interest of accuracy. Think I'll post this question to the MS designers on the FSX forum and see if they are going to address this bizarre problem in the next version. Could use some other collaboration on that post to get attention to it probably.Art

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The magdec.bgl file defines the compass bearings displayed on your airplane's instruments. This includes the magnetic compass, HSI, Shift-Z information display and GPS.Each airport has a defined magnetic variation in the ap*.bgl file. As far as I can see, this element does nothing but allow the ATC to calculate the correct bearings to the airport. There are also magvar elements for each ILS, which serve the same purpose.It's worth noting that the information in magdec.bgl seems to represent a 1985 magvar model, while the ap*.bgls appear to contain 1995 information. This means that when you are shooting an ILS there will be a slight difference between the heading on your compass and the heading shown in the map view dialog.Hope this helps,Todd

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I had this same issue with my KCLE scenery. It appeared to be caused by an earlier version of scenegenX. When I recompiled with the newer versions it was OK. I think the problem was to do with the ILS of the runway.Shez

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A recent Lisbon scenery, PLPv3.2, happens to have a replacement magdec.bgl file in it. It appears to be the same file I have been using for a while. The author credits Luis Sa for it. Maybe Luis is following this forum?scott s..

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