!!!!!!!???????!!!!!!!!
- From: "Ahmed Ouahi, Architect" <ahmed.ouahi@xxxxxxxxx>
- Date: Tue, 5 Sep 2006 00:32:50 +0300
However, you do have to keep in mind, that a 1-month difference in a date is
an equal to a 2-hour difference in a time of a night., for instance,
anything observed at 9 : 00 p. m., on July 15 would be at that same location
at 7 : 00 p. m., on august 15, a definitely as a matter a fact.
--
Ahmed Ouahi, Architect
Best Regards!
"Paul B. Andersen" <paul.b.andersen@xxxxxxxxxxxxxxxx> wrote in message
news:edi3fa$1bn$1@xxxxxxxxxxxxxxxxxxx
Sorcerer wrote:message
"Paul B. Andersen" <paul.b.andersen@xxxxxxxxxxxxxxxx> wrote in message
news:ed6of0$qjj$1@xxxxxxxxxxxxxxxxxxx
| Sorcerer wrote:
| > "Paul B. Andersen" <paul.b.andersen@xxxxxxxxxxxxxxxx> wrote in
automatic.| > news:ed47qc$mts$1@xxxxxxxxxxxxxxxxxxx
| >
| > You ignored what I wrote. Allow me to do the same.
| >
| > As long as ALL the satellites are wrong by the same amount,
| > it doesn't prevent GPS from working to within its stated
| > accuracy. Again, tB is computed in the receiver and will be
| > 38 usec a day wrong, but the receiver's owner will not
| > notice it, he is looking at HOURS. It is tB-tA that matters,
| > not tA alone. Hence (tB+38) - (tA+38) = tB-tA and the
| > distance is found.
|
| Yes, this is true.
| If all the satellite clocks are wrong by the same amount within 100ns,
| and the error is so small that the error in the satellite position
| can be ignored (38 us is this small),
Position is not time. I have no idea where you come up
with such a crazy idea. Are you drunk?
I suspect you are.
The receiver knows the position of the satellite at any time,
and will thus know where the satellite was when the signal
was transmitted. If the satellite clock is wrong, the receiver will
get the position of the satellite wrong. But 38 us will be negligible
in this context.
Don't you know anything?
How did you think the receiver knows the position of the satellite?
then the receiver will get
| the position right. (It will get the time 38 us wrong, though.
| But that will hardly matter.)
It would matter if it got an hour wrong, though, yet it would still
finds position correctly, (tB+1hour)= (tA+1hour).
The Earth is divided into 24 time zones of 1 hour.
That is 24 * 60 = 1440 time zones of 1 minute,
1440* 60 = 86400 time zones of 1 second.
The circumference at the equator is 24,901.55 miles,
so at the equator a one hour time zone corresponds to
1037.56 miles,
and in North America, home of the GPS, about 700 miles
to the hour.
An Englishman visiting Washington DC (capital)
and an American visiting Trafalgar Square, London (capital)
( they don't often come to Kristiansand -- not capital -- the
back of beyond)
can check the time of his GPS receiver
against the shadow of the Washington Monument or Nelson's
Column, to within 38 usec or 1/2 a bloody inch!
Have you got it NOW, or are you still drunk?
You obviously are.
Because you are not this stupid sober, or are you?
|
| Please read the following, and think while you do so.
| You can if you will (and are sober?), so don't go into your
| "won't listen, snip everything, don't even try to make sense"-mode.
|
| Satellite clocks won't stay equally wrong by themselves.
Thinking... yes, that is why uploads are regular and automatic.
| It would be exactly as hard to keep them equally wrong,
| as it is to keep them equally right.
Thinking... yes, it would. That is why uploads are regular and
| This is why:
| There are three ground stations
Thinking... No, there are five. Wrong again, tusselad.
Why the hell don't you read the whole sentence before
you answer?
There are three ground stations _which can upload data
to the satellites_, NOT five.
| which can upload data
| to the satellites. Each ground station sees each satellite
| once a day.
Thinking... Wrong again, tusselad. The period of the
GPS constellation is 12 hours, not 24. That is twice a day.
You ARE drunk.
A sober electrical engineer with a degree in mathematics
doesn't make blunders like this.
I will give you a hint:
The Earth is rotating, the orbits are not.
If a satellite passes over your head, where are you
12 hours later, when the satellite have made a full orbit?
Think of it when you get sober - and blush.
That means that it is impossible to upload data
| to each satellite more than three times a day.
Thinking... Wrong again, tusselad. Data can be continually
uploaded from each station whenever the satellite is
in line of sight. With five stations, every satellite is within
sight of a ground station 24 hours a day, it can choose
which TV channel to watch (continually) whenever it gets
bored talking to receivers on the telephone, which these
days is via satellite. Impossible my arse. You are spaced
out on crack cocaine, all I have is a little alcohol.
Do you have ANYTHING that requires me to think?
Babbling drunk.
You can't read, much less think.
When you get sober, you could try to read it again,
while thinking. I am not so naive that I think you
will, though. It seems that your babbling condition
is pretty permanent nowadays.
But here it is again, read it if you are up to it.
There are three ground stations which can upload data
to the satellites. Each ground station sees each satellite
once a day. That means that it is impossible to upload data
to each satellite more than three times a day.
But it is no point in uploading data if there are no data
to upload. Five stations are monitoring the satellites,
finding out the clock error (among other data) of each satellite.
Each satellite must be monitored several times before data
are collected which can be uploaded to the satellite.
In practice are data uploaded to each satellite typically
once a day.
Got it?
-------------------------------------------------------------
The clock in each satellite is synced to GPS-time once a day.
--------------------------------------------------------------
But all the satellites are not corrected at the same time, obviously.
So if the receiver uses four satellites to determine its
position, one clock may be recently corrected, while
others may be corrected several hours ago.
For example:
#1 is newly corrected
#2 is corrected 8 hours ago
#3 is corrected 15 hours ago
#4 is corrected 23 hours ago
If the clock rates were fast by 38 us/day,
the error of each clock would be:
#1 : 0 ns
#2 : 12700 ns ahead of GPS time
#3 : 23800 ns ahead of GPS time
#4 : 36400 ns ahead of GPS time
So the clocks are not "equally wrong" within 100ns.
The position calculated from this would be
wrong by several kilometres!
The only way to keep the clocks correct within 100ns
(or equally wrong within 100 ns, for that matter)
is if the rate of each clock is so correct that it
drifts off sync by less than 100 ns during a day,
equivalent to 10-12.
-------------------------------------------------
The rates of the clocks have to be correct to
a precision better than 10-12 for the GPS to work.
-------------------------------------------------
It is a fact that the satellite clocks are adjusted
to run slow by 4.4647*10-10 prior to launch.
It is a fact that thus adjusted clocks stay in sync
to GPS time to within 100 ns between each correction.
It is a fact that the the GPS wouldn't work without
the pre launch adjustment.
Paul
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