Originally published at: https://boingboing.net/2018/03/03/ever-wonder-how-land-surveying.html
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Darn you, BoingBoing! You do know my weaknesses…
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I had often wondered but never took the time to find out what theodolites did. Thank you BoingBoing. 
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Y’all Americans can help improve the National Spatial Reference System by participating in the GPS on Bench Marks (GPS on BM) campaign, which aims to improve the next hybrid geoid model and make the new 2022 vertical datum more accurate.
https://www.ngs.noaa.gov/GPSonBM/GPSonBM_FAQ.shtml
There’s more videos for the math hungry from the National Geodetic Survey here:
https://www.ngs.noaa.gov/corbin/class_description/NGS_Video_Library.shtml
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Was wondering about this just the other day, thanks!
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I heard a friend of mine geek out a bit over these things once.
He’s a particular kind of engineer that basically looks at your land and tells you how much weight a foundation can support, which spots are suitable for a well or septic system, etc.
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The reference to the Great Trigonometrical Survey of India reminds me of a poignant historical fact.
During the Survey Mt. Everest was simply known as Peak B. It wasn’t until they were in the office doing the math that they determined it was the highest mountain on the world. Being unable to get to the Mountain to learn its actual name they decided to honor fellow surveyor George Everest.
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I had a boss who was too cheap to rent us a TotalStation for some archaeological mapping work in about 2004. He dug out an old brass theodolite in a velvet-lined wood box that due to a quirky math teacher I knew how to use. Some tourist stopped by to let us know how great it was to see us re-enactors using the same tech the plantation had been built with 200 years previously. I explained that actually we were just so underpaid they could afford to waste 5 days of crew time. I’m still not sure where she got the idea re-enactors would wear Carhart pants and t-shirts, but maybe the layer of dirt confused her.
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“Poignant” is one word for it…
Huh, interesting to see how modern ones work.
I was a chainman for a large UK civil engineering outfit back in the early nineties.
That basically meant I was a civil engineer’s assistant, and it was my responsibility to set up levels and the old style analogue theodolytes. Then I’d usually have to climb around partially finished architecture with a staff (referred to as a rod in the video), while the engineer took measurements. If the engineer was particularly hungover, me and another chainman would be tasked with taking the measurements.
I also had to “slump” the concrete delieveries; pour concrete into a fixed-volume cone, measure how much it slumps when removing said cone, then take a cube sample to storage.
I see a lot of the digital theodolytes around London, and have been curious about how they’re set-up for a while now.
Needless to say though, the work’s a LOT messier on an active site.
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I restored an old theodolite I bought at a yard sale ($80). Surprisingly, it’s almost as accurate as a modern digital one (20 arc-seconds). Came with a nice mahogany case, and is my favorite bit of old stuff. https://i.imgur.com/BLOTI.jpg
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I was only bottom-level survey crew in 1977, holding the chain, mostly - but I was the one the boss called into the truck to remember how to work out the angles for “shots” around a curve - because I was on summer from 1st year engineering and knew my geometry.
Now, I feel weirdly privileged to have seen the very last years of pre-digital, pre-laser, pre-GPS surveying. I suppose after the zombie apocalypse, my skills will again be useful with the restored theodolites of hobbyists like some here. For that matter, I think my brother has a highways-dept 1970s theodolite in the basement - basically saved it from the trash after the upgrades came in.
I wonder if distance down a linear construction job like a highway is still referred to as “chainage”. It was a steel tape by 1977, but the one survey truck still had a literal chain in the trunk, sixty-six feet long, with a little screw to adjust its length for the air temperature.
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I just finished reading: Map of a Nation: A Biography of the Ordnance Survey by Rachel Hewitt
Absolutely fascinating, not least in the details described re instrumentation, design and invention thereof, and adjustments needed for air temp and other factors. Highly recommended for anyone interested in mapping / its history / old instruments / measurement methods.
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