NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Sextant Positions versus Map Datums?
From: Jared Sherman
Date: 2002 Jan 15, 11:05 AM
From: Jared Sherman
Date: 2002 Jan 15, 11:05 AM
Okay, a sextant position is based on the almanac which is based on...ergh...How exactly does that match up to a map datum? Should a sextant position line up with a WGS84 chart position? An NAD27? A what-ever-is-most recent datum? Or can it be expected to be off by...What distance actually? If NAD27 and WGS84 disagree by a mile, then wouldn't the "most accurate" sextant position still either be off by a mile, or have been off by a mile? Or maybe still be off wherever the map datum doesn't match a "spherical earth" model? How exactly does one accomodate the "no datum here" from a sextant position? Aside from the fact that the difference may be meaningless out at sea, where the maps all agree that "you are here" in the big empty spaces and a mile or two doesn't always matter.
