I am a Civil Engineer with limited survey knowledge and have been reviewing geodetic concepts and the ellipsoid datums. I came across confusion regarding the origin of GRS80 thinking it was earth centered, earth fixed. But several articles later, I found it was actually tied to the tectonic plates by permanent monuments. But it still remains unclear if the NAD83 datum is actually assumed to be centered on earth or anchored to the ground by monuments / base stations more like the Clarke 1866 datum anchored at meads ranch.
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