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Reverse geocoding is hard

shkspr.mobi

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Re: Reverse geocoding is hard

#91

Post by jandrewrogers »

AlotOfReading wrote: post #85
jandrewrogers wrote: post #65

Earlier quoted context omitted.

GPS coordinates do not account for tectonic motion. It is a synthetic spheroidal model that is not fixed to any point on Earth. The meridians are derived from the average motion of many objects, some of which are not on the planetary surface. The motion of tectonic plates can be calculated relative to this spatial reference system but they are not part of the spatial reference system and would kind of defeat the purp…

The corrections are incorporated into the datum. WGS84 is updated every 6 months to follow ITRF by changing the tracking station locations as the plates move around.

If WGS84 was correcting for tectonic drift it would imply that the coordinates of the terrestrial fixed points used to compute the reference meridian never change under WGS84. Rebasing the coordinates of terrestrial fixed points prior to calculation disregards tectonic drift in the reference meridian calculation, it doesn’t correct it. It is a noise reduction exercise to minimize the influence of plate tectonics on meridian drift. The meridian uses non-terrestrial fixed points too that don’t have a concept of tectonic drift (but may introduce their own idiosyncratic sources of noise).

Basically, these are corrections to their “fixed points” to make them behave more like actual fixed points in the reference meridian model. It doesn’t eliminate tectonic drift effects when using coordinates in that spatial reference system.

Re: Reverse geocoding is hard

#92

Post by [deleted] »

jandrewrogers wrote: post #9

Most people don’t have an intuitive sense of just how technically difficult mapping from real geospatial coordinates to feature spaces is. This is a great example of a relatively simple case. You are essentially doing inference on a sparse data model with complex local non-linearities throughout. If you add in dynamic relationships, like things that move in space, it becomes another order of magnitude worse. We frequ…

[deleted]

Re: Reverse geocoding is hard

#93

Post by sleepy_keita »

jillesvangurp wrote: post #66

This is a while ago but about 12 years ago I experimented with putting the whole of openstreetmap into Elasticsearch. Reverse geocoding then becomes a problem of figuring out which polygons contain the point with a simple query and which POIs/streets/etc. are closest based on perpendicular distance. For that, I simply did a radius search and some post processing on any street segments. Probably not perfect for everyt…

What were some other problems you ran in to when putting OSM in to ES? (I've had this thought before too, I'm curious why/how you did it)

Re: Reverse geocoding is hard

#94

Post by sleepy_keita »

Dachande663 wrote: post #13

Fun fact that was dredged up because the author mentions Australia: GPS points change. Their example coordinates give 6 decimal places, accurate to about 10-15cm. Australia a few years back shifted all locations 1.8m because of continental drift they’re moving north at ~7cm/year). So even storing coordinates as a source of truth can be hazardous. We had to move several thousand points for a client when this happened.

Japan publishes new CRSes after large earthquakes to account for drift. The M9 earthquake in 2011 recorded a maximum shift of 5 meters!

Re: Reverse geocoding is hard

#95

Post by niccl »

pavel_lishin wrote: post #35
Dachande663 wrote: post #13

Fun fact that was dredged up because the author mentions Australia: GPS points change. Their example coordinates give 6 decimal places, accurate to about 10-15cm. Australia a few years back shifted all locations 1.8m because of continental drift they’re moving north at ~7cm/year). So even storing coordinates as a source of truth can be hazardous. We had to move several thousand points for a client when this happened.

Damn! 7cm per year feels blazing fast when you consider the fact that it's a whole continent.

A way to think about it I've seen a few times: continental drift is roughly the same order of magnitude as the rate your fingernails grow!

Re: Reverse geocoding is hard

#96

Post by omcnoe »

xucheng wrote: post #29
Dachande663 wrote: post #13

Fun fact that was dredged up because the author mentions Australia: GPS points change. Their example coordinates give 6 decimal places, accurate to about 10-15cm. Australia a few years back shifted all locations 1.8m because of continental drift they’re moving north at ~7cm/year). So even storing coordinates as a source of truth can be hazardous. We had to move several thousand points for a client when this happened.

Can this be solved by storing a timestamp of the record along with precise GPS coordinates? Could we then utilize some database to compute the drift from then and now?

You don’t need to store a timestamp, but the local coordinate reference system that the coordinates are in. When revisions like this are made, it’s by updating the specification of a specific local coordinate reference.

WGS84 is global, but for most precise local work more specific national coords are used instead.

Re: Reverse geocoding is hard

#97

Post by marc_abonce »

andrew_eu wrote: post #53

I have a memorable reverse geocoding story. I was working with a team that was wrapping up a period of many different projects (including a reverse geocoding service) and adopting one major system to design and maintain. The handover was set to be after the new year holidays and the receiving teams had their own exciting rewrites planned. I was on call the last week of the year and got an alert that sales were halted…

I faced the same issue with locations inside Crimea and Kashmir. The Google Places API wouldn't return a country code for those regions. At the time I couldn't find any documentation from Google specifying which inhabited locations return a null country code, I assume they want to avoid any potential controversy. Unfortunately this lack of documentation makes it harder to work around this issue.

Re: Reverse geocoding is hard

#98

Post by cameldrv »

Dachande663 wrote: post #13

Fun fact that was dredged up because the author mentions Australia: GPS points change. Their example coordinates give 6 decimal places, accurate to about 10-15cm. Australia a few years back shifted all locations 1.8m because of continental drift they’re moving north at ~7cm/year). So even storing coordinates as a source of truth can be hazardous. We had to move several thousand points for a client when this happened.

I think Australia has its own datum for this reason that can float against WGS84

Re: Reverse geocoding is hard

#100

Post by pgreenwood »

xucheng wrote: post #29
Dachande663 wrote: post #13

Fun fact that was dredged up because the author mentions Australia: GPS points change. Their example coordinates give 6 decimal places, accurate to about 10-15cm. Australia a few years back shifted all locations 1.8m because of continental drift they’re moving north at ~7cm/year). So even storing coordinates as a source of truth can be hazardous. We had to move several thousand points for a client when this happened.

Can this be solved by storing a timestamp of the record along with precise GPS coordinates? Could we then utilize some database to compute the drift from then and now?

See https://spatialreference.org/
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