Triangulation (surveying)
Videos
In surveying, triangulation is the process of determining the location of a point by measuring only angles to it from known points at either end of a fixed baseline by using trigonometry, rather than
Triangulation of Kodiak Island in Alaska in 1929.
Liu Hui (c. 263), How to measure the height of a sea island. Illustration from an edition of 1726
Meridian arc
Videos
In geodesy and navigation, a meridian arc is the curve between two points near the Earth's surface having the same longitude. The term may refer either to a segment of the meridian, or to its length.
The north and south sections of the meridinal survey met at Rodez Cathedral, seen here dominating the Rodez skyline at left.
A copy of the "provisional" metre located in the wall of a building, 15 rue de Vaugirard, Paris. These metres were provisional (French: provisoire) because the expedition and the calculations to determine the definitive length of metre were not completed until 1799.
Montjuïc Castle in Barcelona, Spain – the southern end of the meridian arc