Back in the mid 2000's I tried to point out to the people writing the UK BIM standards why it was a bad idea to have all buildings drawn relative to the OS grid datum which is somewhere southwest of the Scilly Isles for exactly this reason. I even tried to explain that computers can't do accurate floating point calculations and they didn't believe me! And then CAD consultants are surprised when automatic 2D drawing generation from 3D models randomly fails to work properly (usually at 10pm the night before a big deadline) and then everyone wonders why architects are backwards and don't want to adopt 3D processes...
I used CAD software back in the late 90's called Spirit. The floating point calcs were infuriating. You could draw a bunch of lines with exact length and offset them by exact distances and trim them and they'd all end up x.01mm etc. when you measured or dimmed them.
Hah, people used to say. We've always used drawing boards, that kind of accuarcy isn't important.
But I'd argue that it was. For my own sanity. Sadly, a standard UK brick is 215 x 102.5 x 65mm. Are bricks manufactured to a tolerance of 0.5mm? Can a builder measure to 0.5mm? No.
But when you're digital, and you have a large building, small errors start to accumulate. Next thing is you have the builder on the phone saying the overall length of your building on opposite sides don't match, which one is correct?
Interesting. For infrastructure projects like roads and railways the standard I'm familiar with is still to just draw them directly based on the national coordinate system, but then again we're also still mostly outputting 2D drawings.
Thankfully it seems that at least with 2D drawings and AutoCAD the worst side effect these days is that under certain circumstances hardware acceleration causes curves/curve segments to be displayed slightly offset. Strangely (but also luckily) enough it never happens when using just AutoCAD, but only when our road/railway design add-in is active (which displays all its output inside the AutoCAD drawing itself) [1], and it doesn't affect points picked via object snapping, i.e. it's really only the display that's affected.
Our friends in structural engineering or architecture on the other hand do indeed use local coordinate systems for their 3D models, though I can't say whether that practice is absolutely universal
[1] Edit: And also in the layout view, but thankfully definitively not in regular model space, where you'd be actually editing things.
This is why I can’t fathom why fractional inches didn’t become the dominant system once engineers switched to CAD. Or not necessarily inches, but at least a fractional representation.
