A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2015 Aug 19, 13:31 -0700
David Pike, you wrote:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2015 Aug 19, 13:31 -0700
David Pike, you wrote:
"One thing this discussion shows is how remarkably accurate the lat and long readout on Google maps, which is presumably tied to WGS84, can be."
Yes, it's amazing, isn't it? And as another example, you can take the latitudes and longitudes in that "Table 1" in the article and visit all those former transit instrument locations all around the globe. In the bar graph I posted, you'll note that there is one location where the change in longitude is 14.5 seconds of arc. That's a lot, amounting to nearly one second in time. The estimate of the east-west tilt there is a nearly perfect match. So where would we get such a "tilted" platform? This site is listed as "San Juan". That's column SJ on the barchart. Its latitude and longitude are 31°30'34.0"S, 68°37'25.6"W (the link takes you there in Google Maps). If you zoom out, you find you're in the foothills of the Andes nearly due west from Buenos Aires. That's exactly the sort of place where you would expect a significant gravitational anomaly.
In addition to the issues Robert Wyatt mentioned, it's also worth remembering that the "satellite images" (often aerial photography rather than actual 