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    Re: Latitude by Talcott-Horrebow Method
    From: Paul Hirose
    Date: 2018 Nov 8, 23:30 -0800

    On 2018-11-07 16:15, Brad Morris wrote:
    > Okay, so now I am just a bit confused.  The geoditic monuments that
    > Peter mentioned must have their asigned latitude and longitude changed
    > as they move about due to plate tectonics, or so it is stated. But are
    > they also reassigned as a function of pole wander?
    No. In fact, the x and y polar motion values published by the IERS are
    measured with respect to the ITRS pole (which for practical purposes is
    identical to the WGS84 pole). For instance, the wandering pole in the
    diagram below is depicted on the fixed grid of the ITRS.
    > If not, then how are the two systems aligned.  Example of confusion.
    > I take my GPS receiver to a geoditic monument.  The GPS ephemeris
    > updated to include pole wander, as per Paul.  So the geoditic latitude
    > will NOT match the GPS latitude.
    To the contrary, the coordinates *will* match due to the peculiar way
    the quasi Keplerian orbital elements of the GPS satellites are
    constructed. Normally, Keplerian elements yield a satellite position in
    some inertial (non-rotating) coordinate system. But the GPS "Keplerian"
    elements yield a satellite position with respect to the WGS84, which
    rotates in space once per day. Furthermore, it's a wobbly rotation since
    the WGS84 pole is misaligned with the axis of rotation by tenths of an
    arc second.
    I had never heard of Keplerian elements used this way and wouldn't have
    thought it possible. The rotation of Earth and the pole offset are baked
    into the orbital elements so the solution comes out in the WGS84. What
    would Kepler have thought?

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