I feel like many people in this comment section don’t understand the difference between CAD data and GIS data. It’s true that 3d models can be built and put into game engines and has been for some time, but GIS data is specifically geospatial data. It’s not a model of a building and never was. The models of buildings in this article are NOT gis data. The ground is the GIS data.
When we build models of buildings for engineering planning purposes we get a surveying crew to physically measure the relative positions and elevations of many points on a map so that the ground in the ‘model’ is representative of the ground in reality, from which you can plan cut and fill, figure out challenges, etc.
The shitty models of buildings so that execs can ‘see’ the space are not GIS data, and were never meant to be. They’re just visualization. The execs won’t know if something is shifted over by a bit, but the engineer needs to know, and it has to be more or less perfect.
I looked at building information model (BIM) standards a while ago. There are apparently some EU rules that new buildings should have a BIM. This sounds great until you realize what that means is that some cad file needs to get converted into that format and that that file is typically created and never updated before anyone moves into the building. A fun little exercise is trying to get your hands on such a file for any given company building. It exists, somewhere (because it has to). But finding out where is going to be interesting. Typically nobody in companies knows anything about any of this. And when you finally find a BIM file, chances are it isn't very useful. I've seen some samples. It's just a lot of vector data without context, semantics, etc. They are basically technical drawings and not intended to look pretty or nice.
Extracting usable, attractive 3D (or 2D) models from that is a non trivial exercise and I know of a few companies that do this. It's a lot of work, typically and only half automated.
GIS data can be 3D by the way. E.g. geojson uses an array for coordinates and the third position is reserved for altitude. It's just that a lot of GIS data sets don't include altitude information.
One interesting aspect of GIS data is that coordinates are not exact. They can be off by meters and misaligned with other data sets. I've had lots of fun trying to align floor plans with maps and image satellite imagery from different sources. They don't agree with each other where things like building coordinates are. Switching between Apple, Google, and Openstreetmap you may get a slightly different map. It's very common for roads to not be exactly aligned with the satellite imagery. If you think about it, there are all sorts of things that can introduce errors. GPS is not perfect, you get perspective problems with aerial photography. And tectonic plates actually move around. Not very fast, usually. But it adds up over the years. In many places it's centimeters per year. Everything combined, your average map is accurate to about a few meters at best.
>GIS data can be 3D by the way. E.g. geojson uses an array for coordinates and the third position is reserved for altitude. It's just that a lot of GIS data sets don't include altitude information.
yes, its why I said relative positions and elevations.
>One interesting aspect of GIS data is that coordinates are not exact. They can be off by meters and misaligned with other data sets.
It often depends on relative projection etc. The coordinates are exact, but if you're getting them from a source with a relatively high inaccuracy they may just be wrong, or disagree with another data source. As I said, when it really matters a survey crew goes out and does things to a much higher degree of accuracy than 'a few meters', or a lidar scan takes very accurate measurements that are accurate to mm not meters.
The case in the article where they're looking at a construction site and making decisions based on the information would get a digital file from the survey crew based on a nearby survey benchmark, not from GPS. When using actual surveying tech based on GPS the accuracy is much higher than 'GPS', and errors in properly done surveys are something like 3 cm in 30km.
The issue is that people are using data not intended to make detailed plans, to make detailed plans, because they don't want to pay for surveying. When surveying is paid for, the map is accurate to millimeters not centimeters or meters as you say.
Tectonic plates shifting are unlikely to be a measurable issue in the overwhelming majority of projects unless you have very very long term projects that are very large, in which case the thermal expansion of materials is likely to make a much larger variability than any plate movement.
When the article is about something you're familiar with, you do start to wonder if all HN comment threads are similarly topped by blowhards missing the point.
When we build models of buildings for engineering planning purposes we get a surveying crew to physically measure the relative positions and elevations of many points on a map so that the ground in the ‘model’ is representative of the ground in reality, from which you can plan cut and fill, figure out challenges, etc.
The shitty models of buildings so that execs can ‘see’ the space are not GIS data, and were never meant to be. They’re just visualization. The execs won’t know if something is shifted over by a bit, but the engineer needs to know, and it has to be more or less perfect.