Comment on How are roundabouts made?
Ziggurat@jlai.lu 1 day ago
Have you seen these people with a weird tripod on construction sites ? They’re surveyor and have tools allowing them to do very precise measure (A guy told me that one of the coolest things he has done was to make sure railway track were aligned below 1mm on both side of 2 km bridge to build) I would expect that drawing a circle isn’t that complicated.
Then the rest is usual road construction, add temporary marking, close the road, do the measurement and build the roundabout
Valmond@lemmy.world 1 day ago
The tripods only measure height though? Or are there newer fancier ones around nowadays?
Ziggurat@jlai.lu 1 day ago
Distance too. I used a surveyor for some precision measument, and their theodolite has 20 micrometer of systematic error.
spankmonkey@lemmy.world 1 day ago
The tripods they look through have always allowed them to measure things in a way that results in elevation, distance, and some other stuff too.
eltrain123@lemmy.world 1 day ago
I used to be a surveyor! The tripods have different tools you can put on top.
A ‘level’ is used to look at rod (some distance away) with measurement gradations on it, like a ruler, to add or subtract height from its current position to determine elevation. You can transfer measurements long distances by leap-frogging positions of the level and the rod. If you start or end at a known USGS monument, you can tie into historicity known elevations. This is how elevations were mapped before GPS (but the survey markers are still used today). They have some really fancy auto-levels that read a qr-style barcode and can measure down to very precise heights.
A ‘thedolite’ is a robot-style machine that uses triangulation to determine elevation, distance, and angle. You benchmark it in place so it knows its location, then uses a rod with a prism it can follow. It calculates degrees it turns horizontally and pivots vertically to calculate where you are with the prism. It will automatically guide you to pre-programmed points to lay out very precise locations. Or you can use it to capture really precise points that are in the field. I haven’t been a surveyor in 20years, but they could easily layout points to millimeter accuracy when I was in the game.
We also used lidar scanners to capture ‘as-built’ maps or calculate volumes of material. A lidar scanner shoots out a laser a few 100,000 times a second as the s amber turns on the tripod. When it bounces off an object, it returns a x,y,z coordinate and a color of the object it bounces off of. When you get a few million returned, you get a point cloud that represents the physical area you are mapping. When you move the scanner and repeat the process, you can map out large areas to a pretty high degree of accuracy. We once used a scan of a statue that was built in the 1800s to compare against the weight of construction materials so we could calculate the crane load expected to move it. Pretty cool stuff!
Valmond@lemmy.world 10 hours ago
Thank you!