4 ms·

Australia updated its latitude and longitude somewhat recently because of continental drift: > The Geocentric Datum of Australia, the country’s local coordinat

Australia updated its latitude and longitude somewhat recently because of continental drift: > The Geocentric Datum of Australia, the country’s local coordinate system, was last updated in 1994, and Australia is now about 1.5m further north-north-east (or, to give the metric used in a BBC infographic: about the height of a kangaroo). * https://www.theguardian.com/science/2016/aug/03/mind-the-gap-australias-latitude-and-longitude-to-shift-2m-next-year https://www.theguardian.com/science/2016/aug/03/mind-the-gap... * https://www.ga.gov.au/scientific-topics/positioning-navigation/geodesy/datums-projections/gda2020 https://www.ga.gov.au/scientific-topics/positioning-navigati... * https://www.australiangeographic.com.au/topics/science-environment/2017/02/how-gps-keeps-up-with-australias-continental-drift/ https://www.australiangeographic.com.au/topics/science-envir... To anyone working in the GIS industry: how would one go about doing a 'mass update' of locations of an entire country in maps and firmware and such?

dboreham 3y ago
Locations inside a country (e.g. plat map boundaries) don't use latitude/longitude.
- taeric 3y ago
  They didn't used to. And, of course you are correct that survey markers are to landmarks. But, more and more people are using data from online mapping services, that largely think they can store locations in lat/lng. People seem to trust that as "the UTC of location data." That said, those can be just as fraught, no? Since movement will not be fully uniform for the entire continent? And landmarks aren't static things, either? I'm curious how landmarks are done to preserve this, long term?
  - tmm 3y ago
    > And landmarks aren't static things, either? I'm curious how landmarks are done to preserve this, long term? At least in the US, the people in charge of this (the National Geodetic Survey) take movement into account. This[1] is the datasheet for the reference monument nearest my house. It has data for 3D velocity of the reference point. VX = -0.0150 m/yr northward = 0.0040 m/yr VY = -0.0008 m/yr eastward = -0.0148 m/yr VZ = 0.0030 m/yr upward = -0.0002 m/yr I'm not sure what the difference is between VX/VY/VZ and northward/eastward/upward, but those numbers are bigger than I thought they'd be. 15 mm/yr seems like a lot! The official coordinates get updated from time to time, and in-between, perhaps you're supposed to adjust your measurements using that movement data (IANAS)? If there is a significant measured change in location due to an earthquake, I'm sure that data would be included in the monument datasheet or a new set of coordinates would be published. FWIW, I went looking to see when the last earthquake was here in Maryland and it turns out there was one today[2]. [1] https://www.ngs.noaa.gov/cgi-cors/CorsSidebarSelect.prl?site=baco&option=Coordinates14 https://www.ngs.noaa.gov/cgi-cors/CorsSidebarSelect.prl?site... [2] https://www.abc27.com/news/top-stories/2-3-magnitude-earthquake-shakes-portion-of-maryland/ https://www.abc27.com/news/top-stories/2-3-magnitude-earthqu...
- eesmith 3y ago
  Some places use an encoded lat/long. Open Location Code - "Google has shown practical usage of plus codes for addressing purposes in Cape Verde,[10] parts of Kolkata[11] and Kolhapur[12] in India, and the Navajo Nation in the United States.[13]" - https://en.wikipedia.org/wiki/Geocode https://en.wikipedia.org/wiki/Geocode . https://freethoughtblogs.com/singham/2023/12/24/using-olc-coordinates-as-addresses/ https://freethoughtblogs.com/singham/2023/12/24/using-olc-co... says a friend of his sent an OLC coordinate to get to a place in Carmel-by-the-Sea, California, which (infamously?) has no street numbers. What3words - "This population had "no consistent addressing system" until May 2016 when Mongol Post started using a geocoding system provided by what3words." - https://en.wikipedia.org/wiki/Mongol_Post https://en.wikipedia.org/wiki/Mongol_Post Over time (centuries?) the named coordinate will no longer be valid as the location is no longer near enough to that lat/long.
  - midasuni 3y ago
    I believe W3W are 1m squares, so in Japan it sounds like they may be already broken
    - eesmith 3y ago
      https://en.wikipedia.org/wiki/What3words https://en.wikipedia.org/wiki/What3words says "What3words divides the world into a grid of 57 trillion 3-by-3-metre (10 ft × 10 ft) squares". Australia moves about 7cm/year so after about 43 years a W3W coordinate no longer matches local coordinates. It feels weird that a continent could move so much in someone's lifetime. Looks like the 1906 San Francisco quake had displacements up to 8.5 meters, so more than two squares. https://en.wikipedia.org/wiki/1906_San_Francisco_earthquake https://en.wikipedia.org/wiki/1906_San_Francisco_earthquake
taeric 3y ago
I'm also curious if anyone has a good article to read on how this is managed. My guess would be that you have reference points and sets of nearby things that are recorded relative to the closest reference point. As noted in the sibling, your plat map is likely set against a local landmark. (Though, even there, they often also include the lat/lng of where it is expected to be found.)
- gwright 3y ago
  This is a good example of why capturing coordinates in a local spatial reference system may be better than capturing coordinates in a global spatial reference system. Global coordinates of a place of interest will drift relative to a global coordinate system but remain stable relative to a local coordinate system. This article illustrates that "stable" is not the same thing as unchanging in the presence of 7.5 earthquakes.
  - midasuni 3y ago
    It’s similar to capturing future dates in local time including timezone. There’s no guarantee that 1300 london time on 20-Dec-2029 will be 1300UatC, as the U.K. may shift its daylight rules before then.
    - sangnoir 3y ago
      That depends entirely ok whether the event being reflected is local or global. If its the time of an solar eclipse, for example, then its unaffected by daylight rules - unlike business hours and such. Working with dates/timestamps is a nightmare, but appears simple at first blush.
chrismorgan 3y ago
Australia’s geocentric datum is pretty boring, because Australia’s tectonics are pretty boring. We just don’t get large earthquakes. So the GDA94 → GDA2020 update is actually pretty minor. If my understanding is correct, the 1.8m difference sometimes talked of between ITRF92 and GDA94 by 2020 is actually irrelevant so long as you do proper projection of your coordinates, which you should, but some things don’t—and so tweaking your reference point from time to time to compensate is pragmatic (in part because it lets people skip deformation models where a metre or so of accuracy is adequate, so temper my “should”). The GDA94 → GDA2020 update is more about certain changes in ITRF1992 → ITRF2014 (~9cm changes in ellipsoidal heights), and local crust deformations. Mass updating from GDA94 to GDA2020 is an easy reprojection. In saying GDA94 is actually fine as far as continental drift is concerned: the thing most people don’t realise is that all of these coordinate systems are actually time-dependent transformations: they’ve got forecast continental drift baked in. So later datum updates just need to record what actually happened, if it was different enough (which it will be in places). Now real earthquakes—they make things much more interesting. I like what https://www.linz.govt.nz/guidance/geodetic-system/coordinate-systems-used-new-zealand/geodetic-datums/new-zealand-geodetic-datum-2000-nzgd2000 https://www.linz.govt.nz/guidance/geodetic-system/coordinate... says: > Some earthquakes, such as those of the Canterbury earthquake sequence starting in 2010, have caused metres of movement. Where this has happened we have updated the coordinates rather than simply include the movement in the deformation model. This is necessary as otherwise the coordinates will not be accurate enough for many applications. The deformation model still includes the earthquake deformation, but it is applied in reverse to transform coordinates for dates before the earthquake. The deformation model page <https://www.linz.govt.nz/guidance/geodetic-system/coordinate-systems-used-new-zealand/geodetic-datums/new-zealand-geodetic-datum-2000-nzgd2000/nzgd2000-deformation-model https://www.linz.govt.nz/guidance/geodetic-system/coordinate...> is also rather interesting, giving details of when they’ve released new deformation models, including both forward and reverse patches due to earthquakes, and it’s messy. I haven’t thought too deeply about the reverse patching technique (this isn’t a domain I work in) but I don’t think I like it (though it may be pragmatic) because it messes with epoch-era NZGD2000 points, seems to undermine the purpose of a datum unless you have recorded the coordinate times as well (rather than merely transforming to the epoch, which has now been spoiled). Did have a fun chat with a telecommunications field worker that I happened to meet when I was in New Zealand in 2021, who had a lot of interesting experience after the 2016 Kaikoura earthquake. Lots of stuff I’m not used to thinking about, coming from boring old Australia.
fragmede 3y ago
Falsehoods programmers believe about landmasses.

dboreham 3y ago

Locations inside a country (e.g. plat map boundaries) don't use latitude/longitude.

taeric 3y ago
They didn't used to. And, of course you are correct that survey markers are to landmarks. But, more and more people are using data from online mapping services, that largely think they can store locations in lat/lng. People seem to trust that as "the UTC of location data." That said, those can be just as fraught, no? Since movement will not be fully uniform for the entire continent? And landmarks aren't static things, either? I'm curious how landmarks are done to preserve this, long term?
- tmm 3y ago
  > And landmarks aren't static things, either? I'm curious how landmarks are done to preserve this, long term? At least in the US, the people in charge of this (the National Geodetic Survey) take movement into account. This[1] is the datasheet for the reference monument nearest my house. It has data for 3D velocity of the reference point. VX = -0.0150 m/yr northward = 0.0040 m/yr VY = -0.0008 m/yr eastward = -0.0148 m/yr VZ = 0.0030 m/yr upward = -0.0002 m/yr I'm not sure what the difference is between VX/VY/VZ and northward/eastward/upward, but those numbers are bigger than I thought they'd be. 15 mm/yr seems like a lot! The official coordinates get updated from time to time, and in-between, perhaps you're supposed to adjust your measurements using that movement data (IANAS)? If there is a significant measured change in location due to an earthquake, I'm sure that data would be included in the monument datasheet or a new set of coordinates would be published. FWIW, I went looking to see when the last earthquake was here in Maryland and it turns out there was one today[2]. [1] https://www.ngs.noaa.gov/cgi-cors/CorsSidebarSelect.prl?site=baco&option=Coordinates14 https://www.ngs.noaa.gov/cgi-cors/CorsSidebarSelect.prl?site... [2] https://www.abc27.com/news/top-stories/2-3-magnitude-earthquake-shakes-portion-of-maryland/ https://www.abc27.com/news/top-stories/2-3-magnitude-earthqu...
eesmith 3y ago
Some places use an encoded lat/long. Open Location Code - "Google has shown practical usage of plus codes for addressing purposes in Cape Verde,[10] parts of Kolkata[11] and Kolhapur[12] in India, and the Navajo Nation in the United States.[13]" - https://en.wikipedia.org/wiki/Geocode https://en.wikipedia.org/wiki/Geocode . https://freethoughtblogs.com/singham/2023/12/24/using-olc-coordinates-as-addresses/ https://freethoughtblogs.com/singham/2023/12/24/using-olc-co... says a friend of his sent an OLC coordinate to get to a place in Carmel-by-the-Sea, California, which (infamously?) has no street numbers. What3words - "This population had "no consistent addressing system" until May 2016 when Mongol Post started using a geocoding system provided by what3words." - https://en.wikipedia.org/wiki/Mongol_Post https://en.wikipedia.org/wiki/Mongol_Post Over time (centuries?) the named coordinate will no longer be valid as the location is no longer near enough to that lat/long.
- midasuni 3y ago
  I believe W3W are 1m squares, so in Japan it sounds like they may be already broken
  - eesmith 3y ago
    https://en.wikipedia.org/wiki/What3words https://en.wikipedia.org/wiki/What3words says "What3words divides the world into a grid of 57 trillion 3-by-3-metre (10 ft × 10 ft) squares". Australia moves about 7cm/year so after about 43 years a W3W coordinate no longer matches local coordinates. It feels weird that a continent could move so much in someone's lifetime. Looks like the 1906 San Francisco quake had displacements up to 8.5 meters, so more than two squares. https://en.wikipedia.org/wiki/1906_San_Francisco_earthquake https://en.wikipedia.org/wiki/1906_San_Francisco_earthquake

taeric 3y ago

I'm also curious if anyone has a good article to read on how this is managed. My guess would be that you have reference points and sets of nearby things that are recorded relative to the closest reference point. As noted in the sibling, your plat map is likely set against a local landmark. (Though, even there, they often also include the lat/lng of where it is expected to be found.)

gwright 3y ago
This is a good example of why capturing coordinates in a local spatial reference system may be better than capturing coordinates in a global spatial reference system. Global coordinates of a place of interest will drift relative to a global coordinate system but remain stable relative to a local coordinate system. This article illustrates that "stable" is not the same thing as unchanging in the presence of 7.5 earthquakes.
- midasuni 3y ago
  It’s similar to capturing future dates in local time including timezone. There’s no guarantee that 1300 london time on 20-Dec-2029 will be 1300UatC, as the U.K. may shift its daylight rules before then.
  - sangnoir 3y ago
    That depends entirely ok whether the event being reflected is local or global. If its the time of an solar eclipse, for example, then its unaffected by daylight rules - unlike business hours and such. Working with dates/timestamps is a nightmare, but appears simple at first blush.

chrismorgan 3y ago

Australia’s geocentric datum is pretty boring, because Australia’s tectonics are pretty boring. We just don’t get large earthquakes. So the GDA94 → GDA2020 update is actually pretty minor. If my understanding is correct, the 1.8m difference sometimes talked of between ITRF92 and GDA94 by 2020 is actually irrelevant so long as you do proper projection of your coordinates, which you should, but some things don’t—and so tweaking your reference point from time to time to compensate is pragmatic (in part because it lets people skip deformation models where a metre or so of accuracy is adequate, so temper my “should”). The GDA94 → GDA2020 update is more about certain changes in ITRF1992 → ITRF2014 (~9cm changes in ellipsoidal heights), and local crust deformations. Mass updating from GDA94 to GDA2020 is an easy reprojection. In saying GDA94 is actually fine as far as continental drift is concerned: the thing most people don’t realise is that all of these coordinate systems are actually time-dependent transformations: they’ve got forecast continental drift baked in. So later datum updates just need to record what actually happened, if it was different enough (which it will be in places). Now real earthquakes—they make things much more interesting. I like what https://www.linz.govt.nz/guidance/geodetic-system/coordinate-systems-used-new-zealand/geodetic-datums/new-zealand-geodetic-datum-2000-nzgd2000 https://www.linz.govt.nz/guidance/geodetic-system/coordinate... says: > Some earthquakes, such as those of the Canterbury earthquake sequence starting in 2010, have caused metres of movement. Where this has happened we have updated the coordinates rather than simply include the movement in the deformation model. This is necessary as otherwise the coordinates will not be accurate enough for many applications. The deformation model still includes the earthquake deformation, but it is applied in reverse to transform coordinates for dates before the earthquake. The deformation model page <https://www.linz.govt.nz/guidance/geodetic-system/coordinate-systems-used-new-zealand/geodetic-datums/new-zealand-geodetic-datum-2000-nzgd2000/nzgd2000-deformation-model https://www.linz.govt.nz/guidance/geodetic-system/coordinate...> is also rather interesting, giving details of when they’ve released new deformation models, including both forward and reverse patches due to earthquakes, and it’s messy. I haven’t thought too deeply about the reverse patching technique (this isn’t a domain I work in) but I don’t think I like it (though it may be pragmatic) because it messes with epoch-era NZGD2000 points, seems to undermine the purpose of a datum unless you have recorded the coordinate times as well (rather than merely transforming to the epoch, which has now been spoiled). Did have a fun chat with a telecommunications field worker that I happened to meet when I was in New Zealand in 2021, who had a lot of interesting experience after the 2016 Kaikoura earthquake. Lots of stuff I’m not used to thinking about, coming from boring old Australia.

fragmede 3y ago

Falsehoods programmers believe about landmasses.