NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2018 Nov 7, 17:19 -0500
Peter wrote
Geodetic latitude is a function of monuments anchored to bedrock (and then pointed out it is different then astronomic latitude)
Paul wrote
the rotation of the Earth and wandering of the pole have been absorbed into the ephemeris [ with regards to gps latitude ].
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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?
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.
Maybe you fellows could clarify this for me
Brad
However, nowadays the polar motion is predicted and published a year in advance in IERS Bulletin A to .001″ precision. Bulletin B has more accurate values determined after the fact.The uncertainty of the pole a year in advance is quite a bit larger than 1 mas, though. Bulletin A says the uncertainty is already 13 mas for 40 days out, and gives a little power-law formula that gives 75 mas for a year out. But yes, the measured values are good to 90 uas (~3 mm).Cheers,Peter
