Re: About the F-22 software bug

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

Martin wrote on comp.lang.ada:
> On Feb 5, 6:42 am, Dennis Lee Bieber <wlfr...@ix.netcom.com> wrote:
> > On Thu, 04 Feb 2010 19:46:15 +0100, Pascal Obry <pas...@obry.net>
> > declaimed the following in comp.lang.ada:
> > > I know that the F-22 is 90% of Ada. Is there some public information
> > > about this bug? Is that a design bug?
>
> >         So far as I recall -- from some years ago -- it was an algorithm
> > problem handling position information wrap-around from crossing, as
> > mentioned, the International Dateline... -180.0 to +180.0 deg longitude.
>
> >         I didn't hear that they had to follow the tankers back -- was under
> > the impression once they managed to cross back heading east a reboot of
> > the navigation system started working again...
>
> > --
> >         Wulfraed         Dennis Lee Bieber               KD6MOG
> >         wlfr...@ix.netcom.com HTTP://wlfraed.home.netcom.com/
>
> For some reason (that I don't get at all) lots of systems define long
> as -180 <= x <= +180 degrees.
>
> Having the potential to alias a position seems like a bad idea for a
> start, so when I've been coding such systems up, I've always spent a
> bit of time making it convert positions into the range -180 <= x <
> +180 degrees and using a proper ADT.
>
> I wonder if it was anything to do with that?...

I would have thought a longitude was really a mod 360, shifted by -180
for display purposes? For fractional degrees (i.e. minutes and
seconds), make that mod (360 * 60 * 60), shift by -180 * 60 * 60 and
split in degrees, minutes and seconds when displaying.

--
Ludovic Brenta.