From: mcdonald@skorpio.usask.ca (Shane McDonald)
Newsgroups: rec.aviation.simulators
Subject: Re: FS4 Scenery Rotated - Help
Date: 8 Jan 1993 01:20:45 GMT
Organization: University of Saskatchewan, Saskatoon, Canada
Distribution: world
NNTP-Posting-Host: skorpio.usask.ca

In article <1993Jan7.151104.16783@nntp.hut.fi>, k34386t@kaira.hut.fi (Petri Suominen) writes:
|> In article <1992Dec31.022022.4448@advtech.uswest.com> sbray@advtech.uswest.com (Steven Bray) writes:
|> >Does anyone know why FS4 sometimes has the compass off by any number of
|> >degrees?  Specifically it seems to happen when switching modes.  I created
|> >some scenery which now appears to be rotated at least 10 degrees from what
|> >it should be.  I had been switching modes back and forth to get it correct.

  What I understand this is caused from is built-in "cant" values for
the default scenery areas.  The flight simulator North and East coordinates
don't always line up with the compass.  For example, if you're in LA,
and you go in a direction of 0 degrees (magnetic north), both the North
and East coordinates change (since there is a "cant" value for the LA area),
even though you'd expect only the North coordinate to change.
You can find the compass direction which lines up with N/E coordinate north
by going into slew mode and pressing the ALT key -- your direction will
change, and you'll find that if you move forward, only the North coordinate
will change, even though your heading is something like 335 degrees for LA.

  The reason SubLogic gives for this cant value is something along the lines
of problems with trying to model a round world with a flat plane.

  I think there is a cant value printed on each of the sectional charts, or maybe
it's on the airport charts in the manual.  And, pure speculation here, but
I think that if you add the cant value printed on the charts and the magnetic
variation for an area, you get the heading which points to N/E coordinate north.

  Hmmm, does that make any sense?  So anyways, now that you've got
that straight, Petri says:

|>	That's what happens when you build something outside the basic 
|>	five regions of the US. Get the appropriate scenery disk from
|>	SubLogic and the problem is solved.
|>
|> 	Actually the scenery isn't rotated, it's just your compass,
|> 	VORs, ILSs etc that go bezerck if you try to build something
|> 	"in the nowhere". According to my experience, this deviation of
|> 	magnetic headings depends upon the area where you last were before
|> 	you came to your own scenery.
|> 
|> 	For example if you slew from LA area to FL, You will notice
|> 	that your compass behaves differently if compared to slewing there
|> 	from NY region.
|> 
|> 	The same problem exists in Western European Tour scenery disk
|> 	outside the 3 basic regions.
|> 
|> >Steve Bray

  And the reason for that is, SubLogic only built in cant values for the five
basic regions of the US, and when you go outside one of those regions, you
retain the cant value from the last region you were in.

So, if you are in LA and switch to a Florida mode, you retain the cant value
from LA.  Then, if at some other time you are in New York and switch to a
Florida mode, you will have a different cant value for Florida (New York's),
then all your Florida scenery will appear to have rotated. The scenery all
stays in the same place according to the North and East coordinates,
but the compass thinks the scenery has moved.

  It appears there are two solutions:

1.  Buy the scenery disk for that area.

2.  Everytime you plan to fly your own scenery, follow these steps.  First,
    switch to one of the five basic scenery areas (and make sure it's the
    same one every time you do this).  Then, switch to your own scenery.
    For example, everytime I want to fly some Saskatchewan scenery,
    I always place myself in the Seattle scenery first, then switch to
    my scenery.  This ensures that I've got the same cant value everytime.

  There is a MAGROT.DRV driver with the Aircraft and Adventure Factory
which is supposed to supply cant values for all areas of the continental
U.S.  Has anyone tried it, and do you know if it will solve this problem?
--
Shane McDonald                                       mcdonald@cs.usask.ca
Newsgroups: rec.aviation.simulators