For this reason, many people use the reproducibility rather than instrument precision as the noise floor. It doesn’t matter how precise an instrument you use if the “fixed point” you are measuring doesn’t sit still relative to any spatial reference system you care to use.
In most scientific and engineering domains, a high-precision, high-accuracy measurement is assumed to be reproducible.
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.
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?
This comes up concretely when doing long-baseline interferometry. Lasers are used to precisely measure the distance between receivers in adjacent structures for use in time-of-flight calculations. Over the course of a day, the distance between those structures as measured may vary by multiple centimeters, which is why they measure it.
After 20 years at 7cm per second that's 1.4m. That's the same order of magnitude of error as domestic.
There's a great visualizer of the coordinate velocity from the Earthscope team:
https://www.unavco.org/software/visualization/GPS-Velocity-V...
What?
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.
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 purpose if they were.
IMO having a good land ownership registry is one of the most important things to count as a developed country.
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.
I made neither assumption, and both arguments are irrelevant to my point.
Take the current rights of anyone to one or more plots of land they own. As those are today, and also as they change while some are sold and bought etc.
To protect those rights of those onwers (of citizens and businesses and municipalities and so on) a registry or plots and their boundaries is very useful.
>to decide who gets to use what land inside of said communities
That's a totally irrelevant point, one that I didn't bring up.
I never said the state will happily "award “common” ownership to communities big and small, and as such that it would allow said communities (in many cases much older than the State itself) to decide who gets to use what land inside of said communities". In fact, for the purposes of my argument, whether the state will do that doesn't concern me at all.
Just that the state keeping a registry of plots and their boundaries helps keep track of ownership. Not transfer it to communities, to give it to someone else to administer: to keep track.
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.
If you have only a name field that has a single value that is going to be a crazy workaround. If your names are referencing a person with a date that is much easier. But you need to make that ddcision pretty early.
Of course, you don't get that historical data, but you do get it going forward from there.
Basically you keep an history of all changes so you can always roll-back / get that data if needed?
But this seems like it's probably a better solution.
I think the real magic is it lleverages the WAL (write ahead logs) from pg engine itself, which you could certainly hook up into too, but im not a db expert here
https://mariadb.com/kb/en/temporal-tables/
and if your schema doesn't change much, it's practically free to implement, much easier and simpler than copypasting audit tables, or relying on codegen to do the same.
> 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 system.
[0] https://tidyfirst.substack.com/p/eventual-business-consisten...
A less obvious issue is that to make this work well, you need to do time interval intersection searches/joins at scale. There is a dearth of scalable data structures and algorithms for this in databases.
To correct for these cases you need to be able to separately attribute drift vectors due to the spatial reference system, plate tectonics, and other geophysical phenomena. Without a timestamp that allows you to precisely subtract out the spatial reference system drift vector, the magnitude of the uncertainty is quite large.
WGS84 is global, but for most precise local work more specific national coords are used instead.
I’d imagine older coordinates would work with the earlier CRS?
But I can understand not all coordinates specify their CRS. This have really been an issue for me personally, but I’ve mostly worked with NSW spatial and the Australian Bureau of statistics geodata.
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.