Flights that Cross Midnight

Thanks for the replay.

I see you use a time of flight (we call that the elapsed time of the
flight). We calculate that by converting the depart and arrive local
times to GMT times. But, to get the correct GMT offset, you have to
know the correct date. To know the correct date, you need to know if
it is the depart date or the day after. If I can determine what date
to use to get the arrive station GMT offset, I'll have it made.


(Teacherjh) wrote in message ...

In order to get the correct GMT offset for the arrive station, I have
to know the correct date to use.


Just let your times go past 24:00 and less than 00:00. Then do a check, and
add or subtract a day based on the result. For example, starting with 23:00,
five hours of flight, and a +2 hour offset, you end up with 30:00 on (say)
Tuesday. Then you check to see if the time is 00:00 or =24:00. Since it's
+24:00, add a day and take away 24:00. So now we have 06:00 Wednesday.

Same idea, if you start out at 03:00 Friday, a two hour flight, and a seven
hour offset (the other way) (in the Space Shuttle, presumably!), you end up
with -06:00 (six hours below zero). We check to see if this is 00:00, and if
so, ADD 24:00 and subtract a day. We h ave 18:00 Thursday.

Limit checks like this are common for all date and time conversions (in fact,
any modulo arithmetic with carry). You'll need to check to see if the date
goes past Sunday (day 7) so it can cycle "back" to Monday (day 1), see if you
passed 31 or 30 or 29 or 28 (depending on month and year) so it can cycle back
to the first of Next Month, see if we passed December, etc.

Jose

"ydm9" wrote in message

Programming it is the easy part. Knowing what
to program is the problem. Seeing that I have not received the
solution lets me know that I am in the majority of dumb folks.

If that's how your logic works, your difficulties are understandable. Why
are you asking pilots to answer programming questions? Would you ask
programmers how to fly? There are a number of programming newsgroups that
might be able to help.

"ydm9" wrote in message

If I can determine what date
to use to get the arrive station GMT offset, I'll have it made.

I would think it would make more sense to input the GMT correction, then
calculate any cross-midnight adjustment based on the flight arrival time.
The GMT offset will be a constant (+/- 1 if that locale uses DST) regardless
of your arrival time. Boston is always GMT-4 or -5, and there are only two
dates when the variable comes into play.

"John Gaquin" wrote in message
...

"ydm9" wrote in message

Programming it is the easy part. Knowing what
to program is the problem. Seeing that I have not received the
solution lets me know that I am in the majority of dumb folks.

If that's how your logic works, your difficulties are understandable. Why
are you asking pilots to answer programming questions? Would you ask
programmers how to fly?

Well, ummm, some programmers _are_ pilots :-)


Dima

We calculate that by converting the depart and arrive local
times to GMT times. But, to get the correct GMT offset, you have to
know the correct date. To know the correct date, you need to know if
it is the depart date or the day after. If I can determine what date
to use to get the arrive station GMT offset, I'll have it made.


You need to know which way you are counting, and how many hours you are
counting. I am thinking you start at Rome, and fly west to Calfornia. You
have a time difference of MINUS 8? hours. Sometimes this puts you on the same
day, and sometimes not. This has to do with what time it is in Rome. If
taking eight hours takes you "below zero" then it is the previous day.

Jose

--
(for Email, make the obvious changes in my address)

"Dima Volodin" wrote in message news:ecQmc.12197

Well, ummm, some programmers _are_ pilots :-)

Well, duh! Some surgeons are also woodworkers, but you wouldn't go on a
woodworking NG and ask questions about surgical procedure.

Boston is always GMT-4 or -5, and there are only two
dates when the variable comes into play.

Of course planes depart London on local time, not Zulu.

The U.S. & Britain don't change summer/winter times necessarily on the
same date. (I think the gap is most noticable in autumn.)

(Or perhaps that's what you were saying? But as I recall, the autumn
gap is a couple of weeks.)

all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! blog www.vivabush.org

John Gaquin wrote:

"Dima Volodin" wrote in message news:ecQmc.12197

Well, ummm, some programmers _are_ pilots :-)

Well, duh! Some surgeons are also woodworkers, but you wouldn't go on a
woodworking NG and ask questions about surgical procedure.

Some voters are pilots, and they don't seem to have any problems
discussing all things politics on r.a.p :-)


Dima

"Cub Driver" wrote in message
...

Boston is always GMT-4 or -5, and there are only two
dates when the variable comes into play.

Of course planes depart London on local time, not Zulu.

The U.S. & Britain don't change summer/winter times necessarily on the
same date. (I think the gap is most noticable in autumn.)

No, I meant that there are only two dates when the variable comes into play
for each station. You run the whole thing in GMT, from the computer's pov.

"Dima Volodin" wrote in message
...

Some voters are pilots, and they don't seem to have any problems
discussing all things politics on r.a.p :-)

True, but the OP was asking specific, technical questions on an unrelated
NG, then getting aggravated when good solutions were not forthcoming. Makes
no sense.