Bush to consider shutting down GPS in extreme emergency

Discussion in 'General GPS Discussion' started by Fred, Dec 16, 2004.

  1. Fred

    Mxsmanic Guest

    Tunnels are not always straight.
    It works on the surface, and that's where it was used.
    What good is checking the alignment _after_ digging the tunnel?
    That's a bit late in the game to make any corrections, isn't it?
    There are several ways.
    The Chunnel engineers must have felt differently, since they still used
    GPS.
     
    Mxsmanic, Dec 19, 2004
  2. Fred

    Mxsmanic Guest

    After you've finished digging them, yes.
    I don't think he used lasers.
     
    Mxsmanic, Dec 19, 2004
  3. Fred

    Mxsmanic Guest

    The important datum is WGS-84, the GPS datum. The line can be moved to
    coincide with GPS, if need be.
     
    Mxsmanic, Dec 19, 2004
  4. The 0° Meridian and the Equator are the basis of the whole mapping done
    of the planet ever since. All other systems are based on that.


    Juergen Nieveler
     
    Juergen Nieveler, Dec 19, 2004
  5. You don't dig a tunnel in a single day. Plenty of time to do checking
    and make corrections.
    But you can bet he had surveyors with "ancient" tools like theodolites.


    Juergen Nieveler
     
    Juergen Nieveler, Dec 19, 2004
  6. So why are you claiming they used GPS? The drilling machines were lined
    up using lasers.


    Juergen Nieveler
     
    Juergen Nieveler, Dec 19, 2004
  7. So? You know how far away from straight it's supposed to be, so you can
    measure it.
    The only points of the tunnel where it comes to the surface are the
    exits.
    You check at regular intervals. Alignment can't be THAT bad without
    being spotted by normal eyesight, and checking with the lasers means
    that you notice it soon enough so that corrections still are possible.
    No. A deviation of 5cm over 100m of tunnel can easily be spotted, and
    that's something you can correct.

    Of course, back then the joke went "What do you do if the two crews
    miss each other? Then we'll have two tunnels!" :)
    Not for this kind of tunnel. You can only drill through the rock -
    there was no alternative.
    What for? Please provide some proof on that claim.

    GPS could have been used to map the start points on both ends, and it
    could have been used on the ships that did geological surveys before
    work started - but that's it. GPS cannot be used underground, even you
    have acknowledged that.


    Juergen Nieveler
     
    Juergen Nieveler, Dec 19, 2004
  8. Fred

    Mxsmanic Guest

    Because that's what the references claimed.
     
    Mxsmanic, Dec 19, 2004
  9. Fred

    Mxsmanic Guest

    The tunnel doesn't have to come to the surface.
    To see what mistakes you've already made?
    You said tunnelS.
    To make sure the tunnels were meeting each other.
    Lasers can't be used through solid rock, even you have acknowledged
    that.
     
    Mxsmanic, Dec 19, 2004
  10. Fred

    Mxsmanic Guest

    There are multiple systems, and they aren't necessarily aligned.
     
    Mxsmanic, Dec 19, 2004
  11. Fred

    Alan Browne Guest

    They used GPS indeed to set up ground reference points and controls. The
    drilling under the channel was laser referenced.

    You and I agree on this one.
     
    Alan Browne, Dec 20, 2004
  12. Fred

    Alan Browne Guest

    Juergen Nieveler wrote:

    In a nutshell:

    You need control reference points outside the tunnels: GPS
    You need control of the path while drilling: Lasers/Theodelites

    The GPS networks at one end of the tunnel v. the networks at the other end will
    place the laser references (at each end) with an end to end error of less than
    5mm per km between the two networks. ... about 25 cm all up.

    (Possibly less, some survey systems in use at the time may have been better than
    5mm per 1 km baseline).

    Cheers,
    Alan
     
    Alan Browne, Dec 20, 2004
  13. Simple geometry. Ask your maths teacher. Hint: Right-angle-triangles
    are involved.
    It would be kind of useless if it wouldn't come to the surface at
    some point...
    Yes. And then you correct the mistakes. We're not talking about
    meters here, but centimeter-size mistakes at the worst.
    We were talking about the Eurotunnel.
    Yes. But the parts of the tunnel that already have been finished
    aren't solid rock. All you need to do is make sure that the drilling
    machine goes on straight - and that's easy.

    Juergen Nieveler
     
    Juergen Nieveler, Dec 20, 2004
  14. Fred

    prep Guest

    The cocky maay not use it himself, but almost every Ag plane does, and
    many fire bombers. It is rapidly becoming standard on many broard acre
    ag operations.

    The critical thing will be how many handle the sudden unexpected loss
    of nav data. History already says it will not be pretty...

    If you KNOW that GPS is out, you can cope. A Supertanker losing nav
    signals while all half dozen or so crew are at lunch is another story.

    --
    Paul Repacholi 1 Crescent Rd.,
    +61 (08) 9257-1001 Kalamunda.
    West Australia 6076
    comp.os.vms,- The Older, Grumpier Slashdot
    Raw, Cooked or Well-done, it's all half baked.
    EPIC, The Architecture of the future, always has been, always will be.
     
    prep, Dec 20, 2004
  15. Fred

    prep Guest

    That gets you a good rate, distributing the time is more dificult. NTP
    and GPS have made it unimaginably easy to do that. And low cost!

    --
    Paul Repacholi 1 Crescent Rd.,
    +61 (08) 9257-1001 Kalamunda.
    West Australia 6076
    comp.os.vms,- The Older, Grumpier Slashdot
    Raw, Cooked or Well-done, it's all half baked.
    EPIC, The Architecture of the future, always has been, always will be.
     
    prep, Dec 20, 2004
  16. Fred

    prep Guest

    Want to buy a slightly used C90 or Apache? Very economical, only
    uses 60% of the fuel of others ;)


    --
    Paul Repacholi 1 Crescent Rd.,
    +61 (08) 9257-1001 Kalamunda.
    West Australia 6076
    comp.os.vms,- The Older, Grumpier Slashdot
    Raw, Cooked or Well-done, it's all half baked.
    EPIC, The Architecture of the future, always has been, always will be.
     
    prep, Dec 20, 2004
  17. Not really. They are in intermediate orbits, way below the
    geostationary orbit.

    The other factor is that you cannot use a GPS satellite if it is
    just straddling the horizon. It needs to be up perhaps 5 to 10
    degrees to be useful.

    I guess somebody will have to do the calculation and tell us
    exactly how many percent of the earth's surface are in useful
    view of one GPS satellite. I guess it's something less than 40%.

    Hans-Georg
     
    Hans-Georg Michna, Dec 20, 2004
  18. On 17 Dec 2004 20:09:52 -0000,
    Switching off the GPS system will likely also cost some lives,
    more or less directly. I could imagine a whole variety of
    scenarios in which lack of GPS service threatens lives or
    impedes life-saving operations.

    Also, a certain amount of money can always save lives. The
    question is which ones to save. Saving just any life, no matter
    what, is not possible. People are dying unnecessarily every day.

    Hans-Georg
     
    Hans-Georg Michna, Dec 20, 2004
  19. Stan, Alan,

    thanks for the precise information. I was aware of some of it
    and have to stick to what I wrote above, "Flying a twin while
    knowing that it wouldn't be able to continue after an engine
    failure seems undesirable to me."

    I would think that the only sensible solution when you're higher
    or hotter is to load the plane only so much that you can still
    climb on any one engine.

    Hans-Georg
     
    Hans-Georg Michna, Dec 20, 2004
  20. Fred

    B.Rumary Guest

    B.Rumary, Dec 20, 2004
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