Greg Miller’s crackerjack story in the November 2019 issue of Smithsonian magazine is about the quest to capture German geodetic data—and German geographers—during the dying days of the Second World War. Said data was a strategically critical treasure trove, of immense interest to the U.S. War Department, and the team led by Floyd W. Hough was in a race to find it before it was destroyed, carried away by the enemy, or fell into Soviet hands.
Little is publicly known about the true scope of the information that Hough and his team captured, or the ingenuity they displayed in securing it, because their mission was conducted in secret, and the technical material they seized circulated only among military intelligence experts and academics. But it was a vast scientific treasure—likely the largest cache of geographic data the United States ever obtained from an enemy power in wartime.
The data seized by Hough’s team went on to form the basis of the ED50 geodetic datum, which in turn led to the Universal Tranverse Mercator system.
Geoff Zeiss posts about the forthcoming NATRF2022 datum, which will replace NAD 83 and NAVD 88 in 2022. It will address the shortcomings of the earlier datums and for the first time provide a common datum for Canada, the U.S. and Mexico. “Practically,” Geoff writes, “this means that elevations may change by up to a meter and horizontal location by up to 1.5 meters. The actual corrections to elevations and horizontal locations will depend on where you are in North America. The greatest changes are in the Pacific Northwest and the least in the southeastern U.S.” [Dave Smith]
In response to the news that Australia has to correct its GPS coordinates to account for continental drift, the Ordnance Survey blog examines whether Great Britain will have to do the same. “The situation for us (and most of Europe) is not so bad. Europe’s GPS compatible datum, ETRS89, is fixed to the European tectonic plate at the time 1 January 1989 and moves by around 2.5 cm each year. In theory, GPS-derived coordinates are now about 70 cm away from where they should be in the ETRS89 system.”
Decades of continental drift mean that GPS coordinates in Australia are off by approximately 1.5 metres (5 feet), which has implications for self-driving cars and other applications that require very precise positioning. See coverage from Atlas Obscura, BBC News, Popular Mechanics and the Washington Post.
Basically, the discrepancy comes from the fact that GPS is based on the Earth’s core rather than any point on the surface, whereas local coordinates are based on a geodetic datum—in Australia’s case, GDA94 (North America uses NAD83)—that is based on a fixed point on the surface. But with plate tectonics, points are not fixed: Australia moves northward at seven centimetres a year.
On 1 January 2017 Australia will shift its coordinates north by 1.8 metres, overshooting things a bit so that the continent and GPS will be in sync by 2020, with plans to keep the datum continually updated after that.