Lecture notes - Belépés
2. Reference systems
Land survey is a kind of positioning science. For positioning you need a reference system, sometimes it is called geodetic datum as well. A reference system can be global, national or local. Traditionally horizontal and vertical reference systems are separated because of the different observation techniques. Three-dimensional reference systems are widely used nowadays, especially due to global positioning systems (GPS).
The horizontal reference system is a two-dimensional Cartesian coordinate system, which is defined by its origin, orientation and sequence of axes. Axes of the horizontal coordinate system in surveying is usually oriented to the North and to the East.
The vertical reference system is typically fixed to the mean level of a specific sea. The first vertical datum in Hungary was defined in the 1870s. That time Hungary was part of the Austrian-Hungarian Monarchy and the city and port of Trieste belonged to the Monarchy. That is why the elevations were measured to the Adriatic Mean Sea Level. After the second world war, Hungary was forced to join the Warsaw Pact and the Baltic Mean Sea level was introduced in the 1950s, which is used even nowadays. The constant difference between the two systems is 67.5 cm.