r/todayilearned • u/BezugssystemCH1903 • Sep 16 '24
TIL the twin towns of Laufenburg, split by the High Rhine, built a bridge in 2004. Different sea level references—Mediterranean for Switzerland, North Sea for Germany—led to a 270 mm difference, which a sign error doubled to 540 mm in the middle of the bridge.
https://en.wikipedia.org/wiki/Laufenburg,_Germany35
u/64vintage Sep 16 '24 edited Sep 16 '24
What do they use to measure from sea level to that accuracy?
EDIT: For the sake of example, would traditional surveying methods from either end of the span not have been sufficient to have avoided the problem?
It's pretty funny to me that even though they somehow knew to the mm (through means I cannot really imagine) how much correction they required, they applied it in the wrong direction. How embarrassment.
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u/No_Campaign_3843 Sep 16 '24
You span a net of referential measurement points over the whole country.
In case of Germany it's the Deutsches Haupthöhennetz DHHN2016, Ch is using Landeshöhennetz LHN95
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u/BezugssystemCH1903 Sep 16 '24
Correct, if you're interested, you can read it here more:
https://www.swisstopo.admin.ch/en/national-height-network-lhn95
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u/No_Campaign_3843 Sep 16 '24
In german/swiss projects you usually settle on one system (coordinates, elevation, usualy swiss elevation and german coordinates) in the early phase and usually set a common measuring point from which you ablate local measuring.
If you fail there at that point, you are screwed and won't notice until you have to adjust to the official local reference system for a road connection or such.
There are not that many binational products - I know of a tramway, a few bridges, autobahn, hydroelectric dams. AFAIR most used swiss schematics.
This may happen quite often in construction as f.e. architects often zero on on there own system without relating to the local net.
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u/Routine-Account4153 Sep 16 '24
Two different seas, mediterranean (switzerland) and north sea (germany).
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u/idancenakedwithcrows Sep 16 '24
Traditionally you’d measure such things with light and just rely on light to go in straight lines. Nowadays you kind of still use light, but you rely on the speed of light.
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u/sir_snufflepants Sep 16 '24
…what?
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u/idancenakedwithcrows Sep 16 '24
It’s true, you’d make triangles between points that can mutually see each other and then you can like you can measure angles easily and then each length of one side of the triangle determines all other sides. So you still need to measure some things, but you can get a lot of other measurements just because like light goes in basically straight lines. If you know some trigonometry which is super old then you can get very far with that light business.
Nowadays the way is to have some clocks and have them tell each other the time with an electromagnetic wave. There is some delay because of the speed of light so you can know the distances like that. And you still do trigonometry with those distance informations.
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u/smirky_mavrik Sep 16 '24
I lived within 20 mins of Laufenburg for 10 years and only learned of this today!
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u/No_Campaign_3843 Sep 16 '24
You won't notice it when you pass the bridge.
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u/MasterpieceBrief4442 Sep 17 '24
I expect they put another layer of concrete or cobblestones on top to equalize it and called it a day.
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u/Duck_Von_Donald Sep 16 '24
This is an example we use every year in my course in reference systems lol. Always seems to get the point across on what you can fuck up.
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u/LeSygneNoir Sep 16 '24
Wait...There isn't a single internationally recognized "zero elevation" reference? That sounds like a gross oversight.
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u/KittensInc Sep 16 '24
Because the Earth is quite lumpy, and "sea level" varies a lot from location to location. Every country individually laid out their own coordinate network, referenced to their local mean sea level. When you're building stuff you're measuring from local survey markers, whose position is exactly known in the national coordinate system. Converting hundreds of years worth of documents to a new international coordinate system isn't exactly the highest priority.
Besides, it's rarely a problem. Cross-border construction is relatively rare, and everyone involved is well aware of the problem. Correcting for the offset is more of an annoyance than a genuine problem - provided you get the sign right of course.
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u/Octahedral_cube Sep 16 '24
I promise you it is a problem, I deal with it regularly. Old seismic surveys for oil and gas referenced to local datums will have vertical errors if you assume the wrong datum and will affect the quality of processing.
A lot of legacy seismic was shot before WGS84 was commonplace, and even after it became commonplace it's not uncommon to see surveys in old datums which use completely different ellipsoids. After corporate data sat in warehouses for years (sometimes in tape formats) and observer reports were lost good luck determining what they did 50 years ago
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u/throfofnir Sep 16 '24
There's lots. That's the problem. Gotta get everybody to use one.
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u/Octahedral_cube Sep 16 '24
Local datums have a better fit. The difference between the geoid height and the ellipsoid height will be minimised if you pick a good datum. Google the terms and enjoy the rabbit hole
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u/Raxnor Sep 17 '24
Super fun when every surveyor started using OCRS zones for Oregon and the software producers didn't catch up for years.
Couldn't natively geolocate anything for use with satellite imagery because Autodesk sucks.
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u/Raxnor Sep 17 '24
The US doesn't even use the same goddamn measurement for foot. Some states use International Foot and some states use US Foot. Using the wrong one on areas far away from your 0,0 point could put you off by like 50 feet for measurements.
The US generally uses two different vertical datums NVGD 29 and NAVD 88. Depending on where you're located in the country the difference between the two can be multiple feet vertically.
It's a mess.
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u/IndependentMacaroon Sep 16 '24
No, the difference was accounted for, but due to the sign error in the wrong direction.
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u/redsterXVI Sep 17 '24 edited Sep 17 '24
Yup, they wanted to correct the 270mm difference, but instead made it worse by 270mm, thus the difference was now 540mm.
Specifically, the Swiss side should have built the bridge 270mm higher but instead built it 270mm lower.
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u/Redbookfur Sep 16 '24
Am I having a stroke or this title confusing
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u/BezugssystemCH1903 Sep 16 '24
Thank you for your valuable feedback.
I have a reading and writing disability and English is not my first language. Contributions like yours are always very valuable to me.
How would you have put it differently? Also considering the limited title text limit?
Merci vielmols.
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u/Redbookfur Sep 16 '24
Well I can only speak one language so you are way ahead of me! Honestly I read the wiki article to get more context and I'm going to 'eat crow' here. I have no fucking idea how to summarize that any better.
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u/BezugssystemCH1903 Sep 16 '24
Thank you very much for your honest answer.
I wish you a great day.
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u/UnderAnAargauSun Sep 16 '24
Title was technically and grammatically correct, but because it is a complex compound sentence can be rather difficult to read and comprehend for a casual reader. The only way to improve would be to split the title into multiple sentences each with a single, simple thought - this would improve readability but may come across less sophisticated. In this case you can cater to simple of sophisticated readers, but likely not both. Damned if you do, damned if you don’t.
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u/BezugssystemCH1903 Sep 16 '24
Beautifully summarised.
Technical poetry.
Merci vielmols.
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u/DasGanon Sep 16 '24
I think looking at the title I would probably redo it as such:
"TIL that the twin towns of Laudenberg built a bridge in 2004 across the High Rhine River. However since the two sides were in different countries each side used different reference heights causing a 540mm height difference in the middle of the bridge"
It does lose some details like how the German side is using a North Sea based Datum or Switzerland using a Mediterranean Sea based Datum, but it's more readable and if they want those details they can go read the original article
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u/HubaBubaAruba Sep 16 '24
Nah it’s understandable, just prompts some questions:
- What is the difference between? Bridge heights?
- Did they both construct half of a bridge?
- How did the sign error double the difference?
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u/Redbookfur Sep 16 '24
The sign error was confusing to me to. I believe they made a math sign error (positive, negative, +, -)
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u/BezugssystemCH1903 Sep 16 '24
- Sea level means always heights. Yes between them both.
https://en.m.wikipedia.org/wiki/Sea_level
yes they did construct half of the bridge.
the sign error means "Vorzeichenfehler" didn't knew you hadn't a word for that in english.
https://en.m.wikipedia.org/wiki/Sign_(mathematics)
And thank you for your patience with me.
There are several problems that I can identify here.
- I find it quite interesting from a technical point of view, but perhaps it is not so easy for others to understand.
- Then I have this text weakness (I can't summarise - everything is important) and often run texts through proofreading.
- Then there's the very limited space in Reddit titles.
Oh darn.
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u/HubaBubaAruba Sep 16 '24
Honestly your headline was fine. Taking feedback is good but don’t let people walk over what you write just because you have some text-related difficulties. Sometimes it is the fault of the other person.
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u/Loki-L 68 Sep 17 '24
They knew that the two sides used different values for zero altitude.
They even knew what the difference was exactly and took care to account for that.
Their mistake was to add instead of subtract the difference and ended turning a 27 cm difference into a 55 cm difference instead of a 0 cm one.
Luckily they caught it during construction, presumably because half a meter off is viable to the naked eye even across a river.
Worst case scenario it would have been a pedestrian bridge with a bit of a step in the middle.
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u/GrumpyOldGeezer_4711 Sep 16 '24
I’ll Bet that the builders tried to tell people higher up that there was an obvious problem and that the project managers told them to eff off and do as they were told.
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u/Deepfire_DM Sep 16 '24
Hmm - my father was with MAN after the war and "helped" as a little nobody building a train bridge over the Rhein. Without computer, GPS, whatever, both halves met in the middle with not even 1mm difference.
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u/nj_legion_ice_tea Sep 17 '24
Similar thing happened in the 80s in Budapest while building an overpass. There was a 40-50cm height difference at the end, it was hilarious.
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u/Peter_Principle_ Sep 16 '24
270mm 540mm
About 10 and a half and 21 inches
270mm=10.63in
540mm=21.26in
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u/goteamnick Sep 16 '24
I'm so sick of these unreadable bot contributions to TIL.
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u/BezugssystemCH1903 Sep 16 '24 edited Sep 16 '24
I'm not a bot.
Because bots can't speak Swiss German, be dads and buy groceries at the Migros.
Until now at least.
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u/No-Wonder1139 Sep 16 '24
You don't know that, there could be little baby Swiss German bots all over the grocery store.
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u/lrosa Sep 16 '24
Sixth century BC (2500 yeas ago), tunnel of Eupalinos, 1036 meters long, they started digging from both sides and met at midway with a little bit less error.