David Megginson wrote: > The idea is that users should be able to set any reasonable sea-level > pressure and see reasonable behaviour -- that's why I set the tables > up with deltas rather than absolute values. I can see, now, how that > would be a problem at higher altitudes, but what should we see? If > the altimeter setting at ground level is 28inHG or 31inHG, what would > you expect at, say, 20,000 ft? Would a factor rather than an offset > most appropriate?
Obviously, getting this truly correct is a meteorology problem that requires bunches of scientists and a supercomputer or two to solve. But I'd argue that using a factor would be saner from a flight simulation perspective -- if the sea level pressure at a location is 95% of nominal, then the pilot would naively expect that the air density at all altitudes would be 95% of nominal. Certainly the use of an offset mechanism is going to be surprising, and for the extremes of sea level pressure will lead to super-hurricanes up at altitude. Actually, I'm fairly certain that high altitude phenomena tend to "smooth out" pressure differences down below, so in fact the relative difference between pressures at the flight levels should actually be less than that at sea level. Maybe you could try a factor that asymptotically approaches 1.0 as altitude increases? I don't have much background in meteorology, though. Andy -- Andrew J. Ross NextBus Information Systems Senior Software Engineer Emeryville, CA [EMAIL PROTECTED] http://www.nextbus.com "Men go crazy in conflagrations. They only get better one by one." - Sting (misquoted) _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
