origins of classic trigonometric networks

The paper is a historical overview of beginnings of establishing trigonometric networks to determine the Earth's size and produce accurate maps. First, the book ''Five Books About All Kinds of Triangles'' from 1464 by Johannes Regiomontanus about existing trigonometry knowledge is described. This is followed by mention of Petrus Apianus and his book ''Cosmographicus Liber'' in which Reigner Gemma Frisius published his work in a supplement to a subsequent edition. In it, he proposed using trigonometric networks (triangulation) as an accurate method for determination of points on the Earth. It is little-known that the famous astronomer Tycho Brahe established a trigonometric network in Öresund, intending for it to become the foundation for producing a map of the entire Danish Empire. Unfortunately, he surveyed all required values in the trigonometric network, but did not calculate the trigonometric points' coordinates. Snellius (Willebrord Snel van Royen) was the first to establish a trigonometric network and calculate point coordinates and determined the Earth's size with the greatest accuracy of the time.