Does GPS correct for continental drift, and if so, how? (I'm mainly interested from the perspective of consumer devices such as smartphones.)
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1I'm voting to close this question as off-topic because the person hasn't given the concept of continental drift and GPS precision and accuracy– user681Commented Mar 1, 2015 at 15:37
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3Hi @CyberSkull - welcome to GIS.se - it'd be good if you could expand on your question, indicating the relative magnitude of continental drift, accuracy of GPS systems, and the time frame of interest!– SimbamanguCommented Mar 1, 2015 at 16:32
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If you own your phone for the average 2 years the continents will have moved on average less than a metre (much less than a metre), your smartphone has an accuracy of between 3 and 10 metres (depending on hardware and satellites etc.); the difference between in-hand, in-pocket and on dashboard mounting is far more significant than continental drift - even over the average lifespan of a person (~80 years). Occasionally there are jumps of more significance (earthquakes) but even then the jumps are smaller than the distance from dashboard to hand. Spinal decay would be more significant!– Michael StimsonCommented Mar 2, 2015 at 3:09
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I'm voting for re-opening - while it would be good to get an expanded and more researched question, the first answer here explains some important points about the WGS with respect to what a GPS actually measures which are really worthwhile.– SimbamanguCommented Mar 2, 2015 at 5:10
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My initial reaction was also to close as off topic, but the reason given was more appropriate to downvoting (ie, lack of research effort) than argument supporting 'off topic'. I thought about saying it belonged on another SE site like Earth Science, but the only choice my rep level gets presented with is Meta (short of going the 'other reason' route). But I also looked at Earth Science and a number of GPS questions got negative responses. After consideration, while it might not be 100% on topic here, neither are a lot of other questions. And it's still geographic information science imho.– Chris WCommented Mar 2, 2015 at 23:35
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2 Answers
No, GPS does not 'correct' for continental drift per se. GPS can be (and is) used to measure drift. Drift is accounted for in the model of the earth used, aka datum or reference ellipsoid. GPS uses the World Geodetic System, or WGS, and most units report coordinates in the initial version established in 1984 (aka WGS84 coordinates). That model, and others like it, can be and are revised from time to time. Revisions can account for drift as well as more accurate modeling and measurements.
Technically, it's not the GPS coordinates that change, it's what's located at those coordinates that does since the ground is what's moving. WGS uses the theoretical center of the earth's mass as its origin, so everything on the surface 'floats' relative to that. Some models/datums are tied to a specific plate, in which case everything else on that plate should keep the same relative position (give or take - there's always local fault lines), but things on other plates would 'move'. Here's one of many discussions you can find on the topic.
Now since you're talking about consumer devices and in particular smartphones, the scale of drift occurrence is far beyond the accuracy of such a device. Drift is like 2-4 centimeters per year (disclaimer - figures differ, plates are moving at different speeds, etc.). There are other questions here already on GPS unit accuracy that delve into applying corrections and such, but we'll go with a nice round number of at best 3 meters. In other words, with a consumer device the maximum error for drift within a hundred years is about the same as the potential margin of error between any two given readings from the device.
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Good point: it's the same 'point on the earth' but everything has moved on it; wasn't it Einstein that speculated that everything is relative? Satellite orbits decay as well - but I'm positive that they keep an eye on that! Commented Mar 2, 2015 at 3:12
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There probably is a bit of error, because the shape of the earth is changing (and WGS84 gets redefined every-so-often), but it is almost certainly irrelevant in the total error budget. Commented Mar 2, 2015 at 10:05
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@BradHards, while it may be vanishingly close to irrelevant w.r.t. a GPS, how much does the shape of the earth change? Is it totally encompassed by the WGS84 updates? Commented Mar 4, 2015 at 5:31
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1@Simba WGS84 is a reference system; it does not describe the shape of the earth. The "shape" could mean many things, depending on whether you want to measure the earth's surface or its gravitational potential (the "geoid") and to what extent you are accounting for recurring changes such as the tides, plate movement, and even motions within the atmosphere. To date, the geoid has not been measured with sufficient precision to be able to document changes in a "best fitting ellipsoid." Much of this is described in NIMA TR835.2 (the official WGS84 document).– whuberCommented Mar 7, 2015 at 20:10
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"with a consumer device the maximum error for drift within a hundred years is about the same as the potential margin of error between any two given readings from the device." I'm not sure this is totally correct, in 20 years Australian features move by 1.4m. This is more than the smartphone variance. Australia moved from GDA94 (static) to GDA2020 (dynamic) in order to minimize the increasing offset between GDA94 and WGS-84 (1.8m in average).– minsCommented Apr 8 at 13:33
Not unless you use special software; it only makes sense if your device is firmly attached to earth for year-long periods; see sec. 10.1.1 ("Site Displacement Modeling: Tectonic Plate Motion") in the BERNESE Manual:
Station coordinates are changing in time due to the steady movement of tectonic plates. Figure 10.8 shows the present day major tectonic plates. This movement must be taken into account in GNSS analyses. Station coordinates (especially of reference sites) should therefore always be propagated from the reference epoch to the observation epoch based on corresponding station velocities. This ensures consistency with the IGS satellite orbits and prevents network deformations induced by moving plates.
answered Aug 16, 2015 at 17:15
