[webreac]

I work as contractor for EUROCONTROL. 90% of the time, the usual order (Lat/long) is used in software. When this is not the case, it is a good indicator that I need to be careful about the conventions used to represent all data. I have already encountered the reversed wind direction and more frequently the use of m/s instead of knots (for wind speed).

[supergarfield]

Aren't m/s the correct unit for wind speed? https://en.m.wikipedia.org/wiki/Wind_speed

> Meters per second (m/s) is the SI unit for velocity and the unit recommended by the World Meteorological Organization for reporting wind speeds

> Since 2010 the International Civil Aviation Organization (ICAO) also recommends meters per second for reporting wind speed when approaching runways

[taeric]

This is one of those amusing areas where folks learn that SI units have only been adopted for elementary topics. Storage in a hard drive? Not SI.

Kind of interesting, as well, to consider this when talking about lat/lon. Do those attempt to be SI?

[beerandt]

>Do those attempt to be SI?

Time for SI is still seconds.

Which isn't base-10, yet is SI. So depends on if you accept adopted SI, or want to jump on the base-10 SI clock/time bandwagon.

And lat/lon is based on angles, not distance, with lon coming from time (delta time between solar noon in two locations).

But the SI unit(less) for angles is radians.

So... no, but it depends on how you interpret multiple SI inconsistencies.

[taeric]

Right, I knew that not all SI units were base ten. But I also knew that lat/lon is in degrees, not radians. I also saw the Wikipedia section that knots are still used in industry rather heavily due to their relation to nautical miles. Also not SI.

I recall that astronomical units are also not SI.

Mentioning computers is just a cheap shot, I admit. Still, is valid.

Cooking is an odd one. The old units that were largely defined in thirds are quite useful. Weight is, of course, more reliable for baking, but you can go very far at home quantities with cups and spoons.

To be fair, I'm a large believer that the units are arbitrary and whatever you learned will be good. Such that if you learned SI, it had advantages off the bat. But I am in less agreement that they have an intrinsic advantage.

[beerandt]

Knots and nautical miles are interesting because the nautical mile was originally based on latitude: one minute (1/60 degree) of latitude was 1 nautical mile.

So an airplane traveling due north at 120 knots would cover 2 degrees of latitude per hour.

Most of the US Customary and British Imperial units actually have similar logical definitions or derivations, but they aren't regularly taught anymore.

[taeric]

Right. My point was more that in industries where there is some advantage to keeping a non SI unit, they are want to do so without major external pressure.

So, knots persist because lat lon persists. Home cooks persist with imperial in some places because nobody cares to reprint all recipes and measuring devices. Astrological units because at that scale... Nothing scales. And computers, because binary won. (Curious to consider if ternary had been the winner...)

I confess I am actually personally moved by some of the intuitive arguments for older measurements. Usually very physical based and very in tune with numbers actually used in an industry. It is odd to think of a sixteenth inch wrench, but it is just the natural result of dividing by two, four times, after all. (That is, you have a measuring rod, put a midpoint on there. Four times. Now, do the same for millimeters?). (granted, in the age of computers, any measurement is much easier to do at the machining level.)

[ocyj]

A typical case of the governing body decides one thing but in practice the "since-always" used convention is still preferred I guess? At least this is my experience with dealing with reqs from customers within aviation.

[Leherenn]

Well, if the aircraft speed is in knots (which is generally the case), you'd rather have wind speeds in the same unit.

[icholy]

It's easier to store and process everything in SI units and then convert to the user's preferred unit in the presentation layer.

[nemetroid]

As a rule, yes, but not necessarily and not everywhere. The important part is to have a coherent set of units, which usually is going to be SI units, but not always. If the user's preferred unit never is going to be SI, does it make sense to base your program on SI units?

For example, aviation deals heavily in flight levels (multiples of 100 ft). If flight levels are a first-class concept in your program, then you're already using non-SI units below the presentation layer. At this point you've established that some altitudes in your program are expressed in feet, and it might be a better idea to use feet for altitudes everywhere rather than introducing a lot of unit conversions. Or it might not be.

[Leherenn]

I took it as in the presentation layer, but I can see where you're coming from. In that case I would agree with you, and I'm not sure why GP would complain about that.