zakb on Nostr: npub1npyca…n3sf4 trigonometric stations. You've likely seen stone cairns which ...

npub1npyca9pu08cctq2sxtvkt0uzv9j8ah607a5u7ndwge40f0g2a7ds2n3sf4 (npub1npy…3sf4) trigonometric stations. You've likely seen stone cairns which preceded these. You used to have to unpile the rocks to get to the pin, or some now are stone or concrete pillars with the pins on top. Surveyors used to sight to them using theodolites and triangulate with another to find their position. Nowadays they use GNSS receivers on tripods over the pins that are under the trigs, or secondary pins a few meters away with measured offsets to the trig. They'll set up receivers on a number of control points at the same time and then post process all the satellite data to get a best fit coordinate on the point their wanting, usually a least squares adjustment, which disperses the error across the floating points. Trigs aren't used as much these days as there is so much good control in town and more accessible places, but they are maintained for other projects.

https://en.m.wikipedia.org/wiki/Triangulation_station