The Bulgarian main astronomical point of triangulation was built in 1920 by the Geography institute at the Ministry of War. The geography longitude was determined in 1930 by the prominent Bulgarian scientist academic Vladimir Hristov by simultaneous observations with the geodesic institute in Potsdam. In 1957-58 the point was connected with the main astronomical points of triangulation of Poland, Romania and Hungary.
But what this main astronomical point of triangulation means? I’t a very early version of today’s well known GPS systems.
In trigonometry and geometry, triangulation is the process of determining the location of a point by measuring angles to it from known points at either end of a fixed baseline, rather than measuring distances to the point directly (trilateration). The point can then be fixed as the third point of a triangle with one known side and two known angles.
Triangulation can also refer to the accurate surveying of systems of very large triangles, called triangulation networks. This followed from the work of Willebrord Snell in 1615–17, who showed how a point could be located from the angles subtended from three known points, but measured at the new unknown point rather than the previously fixed points, a problem called resectioning. Surveying error is minimized if a mesh of triangles at the largest appropriate scale is established first. Points inside the triangles can all then be accurately located with reference to it. Such triangulation methods were used for accurate large-scale land surveying until the rise of global navigation satellite systems in the 1980s.