3 ms·

This very phenomenon is why doing GIS work is infuriatingly difficult. A GPS gives coordinates relative to a constellation of satellites, but given how a large

This very phenomenon is why doing GIS work is infuriatingly difficult. A GPS gives coordinates relative to a constellation of satellites, but given how a large chunk of California is drifting a measurable distance, using absolute coordinates would mean all your data on the location of buildings, property lines, and underground infrastructure is increasingly inaccurate. The real world is a complicated, ugly place.

cossatot 10y ago
This is unfortunate for infrastructure but is why we're able to use GPS to measure plate tectonic motions. The geologic consequences of (relative) plate motions are also unfortunate for infrastructure, as well... Out of curiosity, I just checked to see where the fastest velocity on earth relative to a no-net-rotation reference frame is. Using data from the Global Strain Rate Map[0] (I think this is the study, I was emailed the dataset by the first author a couple of years ago), the maximum velocity is on the Philippine Sea Plate immediately east of Taiwan, clocking in at 471 mm/yr. So any undersea points measured in lat/lon (i.e. WGS84) will be inaccurate at almost half a meter per year (or 0.000005 degrees). [0]: http://onlinelibrary.wiley.com/doi/10.1002/2014GC005407/full http://onlinelibrary.wiley.com/doi/10.1002/2014GC005407/full
andyjdavis 10y ago
Curious how you could solve that. I guess you would need to time stamp the coordinates. Then if you had data on how each region has moved you could calculate new coordinates over time. Sounds painful.
- astrodust 10y ago
  There's many, many frames of reference you can use to map your GPS data into actual on-ground coordinates. There's a number of systems that do this, but usually it's done with a projection from abstract GPS points into real-world positions via something like this: https://en.wikipedia.org/wiki/World_Geodetic_System https://en.wikipedia.org/wiki/World_Geodetic_System

cossatot 10y ago

This is unfortunate for infrastructure but is why we're able to use GPS to measure plate tectonic motions. The geologic consequences of (relative) plate motions are also unfortunate for infrastructure, as well... Out of curiosity, I just checked to see where the fastest velocity on earth relative to a no-net-rotation reference frame is. Using data from the Global Strain Rate Map[0] (I think this is the study, I was emailed the dataset by the first author a couple of years ago), the maximum velocity is on the Philippine Sea Plate immediately east of Taiwan, clocking in at 471 mm/yr. So any undersea points measured in lat/lon (i.e. WGS84) will be inaccurate at almost half a meter per year (or 0.000005 degrees). [0]: http://onlinelibrary.wiley.com/doi/10.1002/2014GC005407/full http://onlinelibrary.wiley.com/doi/10.1002/2014GC005407/full

andyjdavis 10y ago

Curious how you could solve that. I guess you would need to time stamp the coordinates. Then if you had data on how each region has moved you could calculate new coordinates over time. Sounds painful.

astrodust 10y ago
There's many, many frames of reference you can use to map your GPS data into actual on-ground coordinates. There's a number of systems that do this, but usually it's done with a projection from abstract GPS points into real-world positions via something like this: https://en.wikipedia.org/wiki/World_Geodetic_System https://en.wikipedia.org/wiki/World_Geodetic_System