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Reverse geocoding is hard

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Re: Reverse geocoding is hard

#101

Post by vintermann »

modeless wrote: post #27
vintermann wrote: post #14

Genealogy applications run into this a lot. The person of interest lived at Engeset. FamilySearch has geocoded a place called "Engeset, Møre og Romsdal, Norway". So that's it, right? Not so fast, [there are at least 3 Engesets in Møre og Romsdal]( https://www.google.com/maps/search/Engeset/@62.3358577,6.225... ). But that's at least better than when it's some local place name which it's never heard of, and thinks sou…

Converting from a name/address to coordinates is geocoding. Reverse geocoding is mapping from coordinates to a name/address.

Well you need both. For instance to know that "Hauan" is likely a small named place near to the other named places this person is associated with, and not the name similar to it in Afghanistan. Any time there's any ambiguity about a name, you need the reverse too, to resolve it.

Re: Reverse geocoding is hard

#102

Post by atoav »

boramalper wrote: post #48
atoav wrote: post #19

Earlier quoted context omitted.

In the past year or so I have thought a lot about how to design tables and columns within databases and there is nearly nothing that wouldn't get more robust by adding in a "valid_from" and "valid_till" and make it accept multiple values. Someone's name is Foo ? What if they change it to Bar at some point and you need to access something from before with the old name? If you have only a name field that has a single v…

See also "Eventual Business Consistency"[0] by Kent Beck. Really good read. > Double-dated data —we tag each bit of business data with 2 dates: > * The date on which the data changed out in the real world, the effective date. > * The date on which the system found out about the change, the posting date. > Using effective & posting dates together we can record all the strange twists & turns of feeding data into a syst…

Thanks for posting this, I read tbis a while ago, but it is worth revisiting.

Re: Reverse geocoding is hard

#103

Post by paganel »

meindnoch wrote: post #88
AlotOfReading wrote: post #85

Earlier quoted context omitted.

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.

That's about correcting the ground stations' coordinates. It doesn't help keeping your house's GPS coordinates fixed. If the tectonic plate your house is built on moves a meter over the course of a decade, then your house's GPS coords will change in the lower decimals, and eventually your government's land registry will need to update those values.

Hopefully there are still governments that don’t keep such in detail land registries, or any land registries at all, for that matter. Some of us don’t want the State to see everything, at almost every moment in time.

Re: Reverse geocoding is hard

#104

Post by timonofathens »

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.

[dead]

Re: Reverse geocoding is hard

#105

Post by hnaccount_rng »

jandrewrogers wrote: post #58
Robotbeat wrote: post #56

Earlier quoted context omitted.

The whole accuracy vs precision thing.

Related but slightly different. The accuracy is real but it is only valid at a point in time. Consequently, you can have both high precision and high accuracy that nonetheless give different measurements depending on when the measurements were made. In most scientific and engineering domains, a high-precision, high-accuracy measurement is assumed to be reproducible.

I think this is a charitable interpretation of the remark which deprives GP from learning something (sorry if this comes across as condescending, I'm genuinely trying to point out a imo relevant difference)

No it's not at all accuracy vs precision. That statement is about a property of the measurement tool, where one can have systematic offsets [0] (think about a manual clock, where the manufacturer clued the finger on with a slight shift) vs they can simply be inaccurate (think about a clock that only has a minute finger, but not one for seconds).

The thing pointed out by the original comment is about a change in the _measured_ system. Which is something fundamentally different. No improvement in the measurement tool [1] can help here as its reality that changes. Even writing down the measurement time is only going to help so much since typically you aren't interested in precisely the time of measurement and will do an implicit assumption of staticness of the real world.

[0] The real reason for those is that it is _much_ simpler to build a precise relative measurement tool (i.e. it's easier to say "bigger than that other thing" than "this large"). One example is CO2 concentration measurements, they are often relative to outdoor CO2, which is - unfortunately - not stable

[1] Assuming that the tool is only allowed to work on one point in time. If you include e.g. a weather modelling supercomputer in your definition of tools, that would again work.

Re: Reverse geocoding is hard

#106

Post by Scarblac »

paganel wrote: post #103
meindnoch wrote: post #88

Earlier quoted context omitted.

That's about correcting the ground stations' coordinates. It doesn't help keeping your house's GPS coordinates fixed. If the tectonic plate your house is built on moves a meter over the course of a decade, then your house's GPS coords will change in the lower decimals, and eventually your government's land registry will need to update those values.

Hopefully there are still governments that don’t keep such in detail land registries, or any land registries at all, for that matter. Some of us don’t want the State to see everything, at almost every moment in time.

And have endless disputes over who owns what exactly? Allow companies to kick people off their land because they can't do anything about it?

IMO having a good land ownership registry is one of the most important things to count as a developed country.

Re: Reverse geocoding is hard

#107

Post by jcattle »

cameldrv wrote: post #98
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

Almost all continents have their own datum. For Japan there's a special case where they now have 18 geodetic zones. Each zone is defined as parts of the crust that tend to move somewhat homogeneously.

Basically after the 2011 Earthquake they had a geodetic mess at their hands, with all coordinates just being all over the place since the ground moved so much. That's why they later on changed their approach.

Re: Reverse geocoding is hard

#108

Post by coldtea »

paganel wrote: post #103
meindnoch wrote: post #88

Earlier quoted context omitted.

That's about correcting the ground stations' coordinates. It doesn't help keeping your house's GPS coordinates fixed. If the tectonic plate your house is built on moves a meter over the course of a decade, then your house's GPS coords will change in the lower decimals, and eventually your government's land registry will need to update those values.

Hopefully there are still governments that don’t keep such in detail land registries, or any land registries at all, for that matter. Some of us don’t want the State to see everything, at almost every moment in time.

If you want to keep your land then you need to keep it in such detail in some registry.

Else it's trivial for someone to claim it or parts of it. Before such registries tons of people lost their land, lost part of their land, went bankrupt trying to save it, or murdered each other over their plots of land border dispute.

There are lots of records a state shouldn't have. Something fixed and stationary that needs protection from encroaching, like land limits, doesn't seem it should be one of them.

Re: Reverse geocoding is hard

#109

Post by [deleted] »

meindnoch wrote: post #87
867-5309 wrote: post #71

Earlier quoted context omitted.

accounts for (something) , phrasal verb meaning "considers; incorporates; takes on board" as opposed to the more obvious "gives rise to; is responsible for". I had to read twice too

Yeah, I know what "accounts for" means. I just can't comprehend how GPS coordinates could account for the tectonic plates' motion. Never heard of such a thing, and can't see how it would work on a conceptual, mathematical level.

[deleted]

Re: Reverse geocoding is hard

#110

Post by raducu »

jandrewrogers wrote: post #47
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.

Even accounting for tectonic drift, there is a concept of positioning reproducibility that is separate from precision. In general the precision of the measurements is much higher than the reproducibility of the same measurements. That is, you may be able to measure a fixed point on the Earth using an instrument with 1cm precision at a specific point in time but if you measure that same point every hour for a year wit…

> if the “fixed point” you are measuring doesn’t sit still relative to any spatial reference system you care to use.

But do those points actually move or the air medium changes the measurements?

I ask because I saw a very interesting documentary once about how they started accurate mapping in England with fixed points and measuring the angles between those points to a high degrees of precision.

My mental model has always been that those points are all fixed, but now that you mention it, why should they be fixed?

After all, my 7 grade teacher clearly demonstrated the thermal deformation or copper rods and all bridges have gaps that allow for thermal deformation, so indeed, this would apply to soil on the scale of tens of kms?

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