NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Longitude shift on NOAA charts vs. Google Earth
From: Lu Abel
Date: 2012 Aug 14, 11:32 -0700
From: Lu Abel
Date: 2012 Aug 14, 11:32 -0700
With respect, Gary, I don't think the NAD27 to WGS84 shift can explain the 1/4 nm (1500 ft) shift George reports. It's on the order of a few hundred feet in most places in the continental US.
I just double-checked -- the chart for Narragansett Bay in Rhode Island says that the NAD-24 to WGS-84 shift is 0.3 SECONDS in latitude, 1.8 SECONDS in longitude. The San Francisco Bay chart lists 0.3" for latitude, 3.9" in longitude. Even using the SF Bay value, that's 1/15 of a nautical mile (or about 400 ft), not the 1/4 mile George is seeing.
George, where location does your chart cover?
From: Gary LaPook <garylapook@pacbell.net>
To: NavList@fer3.com
Sent: Tuesday, August 14, 2012 10:33 AM
Subject: [NavList] Re: Longitude shift on NOAA charts vs. Google Earth
The datum of your chart is most likely NAD 27 (North American Datum of 1927) and Google Earth uses a different datum, WGS 84.
gl
--- On Tue, 8/14/12, G Becker <george@gwbeckerpls.com> wrote:
From: G Becker <george@gwbeckerpls.com>
Subject: [NavList] Longitude shift on NOAA charts vs. Google Earth
To: NavList@fer3.com
Date: Tuesday, August 14, 2012, 8:37 AMSorry if this has been covered before.. On my office wall I have an older NOAA chart (1979). I mark the Lat/Long of various sites on the chart using data from Google Earth. The marks are made in alignment with the NOAA chart scales found around the border. Comparing the two versions of Lat/Long, Google's data is always shifted approximately 1/4 Nautical mile toward Greenwich. Latitude is always accurate. If my data is not incorrect, what would be the difference in the two Lat/Long systems?
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