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Comment by segfaultbuserr | Hacker News Reader

Marginally related: In 2020, the United States finally decided to adopt the International Foot (1959, 304.8 mm, based on the 914.4 mm yard / 25.4 mm inch) for land surveying, which is already the standard that's followed in all engineering disciplines apart from surveying. Now the historical US Survey Foot (1893) will soon been abolished for good.

It's an interesting piece of news, but due to its horrible title, it'll probably never be voted to the homepage (a better title to me would be "The United States finally adopts International Foot, abolishes survey foot").

* America Has Two Feet. It’s About to Lose One of Them

https://news.ycombinator.com/item?id=24196228

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>it'll probably never be voted to the homepage

Incorrect, it was in fact voted to the homepage 7 months ago: https://news.ycombinator.com/item?id=22203919

Or 13 days ago. I know I read it recently--though perhaps on page 2..

https://news.ycombinator.com/item?id=24196228

the fact that the US decided to adopt an "International Foot" which is used primarily only in the US is quite funny :) .

It's similar to how some teams that win the national championship in NFL are called "World Champions"... a sport that is played professionally in only one country.

Back in 1959, when it was adopted, it was still used in a few more countries... and, with Brexit, who knows?

You seriously think the UK will revert to the imperial system? I know they still make some use of imperial measures, but you're implying more than just some legacy imperial, but rather a reversion.

To be fair, when it was invented, it was still in widespread use through the dying British empire.

The US Survey foot is defined as 1200/3937 and the international survey foot is exactly 0.3048 meters. When taking data into applications such as Autodesk Civil 3D, you need to transpose Lat/Long GIS data into a flat Cartesian coordinate system. For example, X,Y values in California start in X=6,000,000 Y=2,000,000 which starts eating up floating point precision. Because 1200/3937 doesn't divide cleanly, you'll end up with varying values depending on where you cut off your precision. That's why Highly Composite Numbers are critical.

Use fixed point?

You'll need rational numbers, not just fixed point, since it's a recurring decimal. (Unless it's a non-recurring decimal in base 2, I guess, but even then, the moment you do something with it you'll probably need a rational representation.)

You lost me there with the 6 million X coordinates in California. 6 million whats starting from where? It can't be feet from the prime meridian, that's not far enough.

I've been scraping my county assessor's GIS database for property outlines and I noticed that the coordinates are huge, as you mentioned. I assumed it was just some fanciful origin but I'd love to know the story.

Probably a https://en.wikipedia.org/wiki/State_Plane_Coordinate_System zone.

Typically designed to have similar error across the whole area and things like that.

Yeah, it's feet measured east and north of an arbitrary point southwest of everything in the state. There is an actual point inside the state used as a base but they set up a false easting and false northing by subtracting a large round number such that the origin of the coordinate system is southwest of everything in the state. A lot of things in surveying are designed such that the math is easier for people working in the field to reliably get correct.

> For example, X,Y values in California start in X=6,000,000 Y=2,000,000 which starts eating up floating point precision.

Why isn't the origin at (0, 0)? It's like saying your ground is at 1,532 volts: You're defining the coordinate system, why make work for yourself?

One reason for the large numbers is that so when data is imported into a drawing it is immediately obvious whether it shares the same coordinate system. If multiple sets of points from different disciplines are imported into the program then the draftsman knows whether the coordinate systems are the same by visual inspection (to a rough degree).

Also because nobody wants to use negative numbers or have the possibility of a negative number showing up.

> “... nobody wants to use negative numbers”

It’s hard to understand these priorities. An unholy mix of base-12 and base-16 is fine, but negative numbers are too difficult to work with?

When you’re working with a couple guys who probably went on a bender last night out in the middle of nowhere with no cell service and a piece of shit walkie talkie that has spotty transmission you sometimes end up having to throw up hand signs to signal northing and easting values. There’s no hand signal for negative. So yeah, negative numbers are hard to work with in that case.

No number has all factors in. Better to work in a way that handles uneven fraction properly than sweep the problem under the rug.

Well, you could just use the first few primes multiplied together as a base. 2 * 3 gives you base6, 2 * 3 * 5 gives you base30. Neither commonly used system does that, base12 uses 2 twice, base10 skips 3. So from a divisibility PoV both are lacking. But arithmetics is base10 anyways, since thats close to the average number of fingers for humans, so...

Does that mean measurements need to specify which kind of foot they are using, in case they might predate the switchover?

It's not so much a switchover as the end of a switchover. The international foot was adopted in 1959, and everything since (at least in surveying) should specify (but often does not, which is one of the reasons the survey foot needs to be abolished)

Uh, you mean 25.4mm as the standard inch? Or that times 12 as the standard foot?

It was a typo, now corrected.

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