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.