Kilometre zero

A fundamental point, also the central point, in classical geodesy was the central point measurement of a country.

Of his astronomical precisely determined coordinates ( astronomical latitude and longitude ), starting by triangulation ( large-scale triangle measurement) was laid out a survey network all over the country.

Classical definition

The fundamental point is - together with a reference ellipsoid and the precise direction of a long side of the triangle - the terrestrial reference system of land surveying Represents the reference system and its orientation are called geodetic datum, the fundamental point and the monitoring network make its realization.

In recent decades, the importance has decreased from fundamental points, because the measurement systems of the States will be converted to intercontinental ellipsoids such as the WGS 84.

Modern definitions

With the emergence of satellite geodesy, there was the possibility to derive the first time geocentric earth models, their characteristics due to the different masses of earth distributions. Since the geodesic computing area now derived in the form of the ellipsoid from a variety of measurements and not from a single point without reference to the geocenter, classic fundamental points have largely lost their meaning. As far as the geodetic datum, so we no longer speak of the date, but the system - because of the manifolds of determining opportunities.

International systems WGS 72 and WGS 84 especially great importance in view of the GPS have become. Many states have changed their country surveys on this geocentric systems.

In Germany, the Potsdam Datum with fundamental point Rauenberg, the Bessel ellipsoid and the conformal Gauss - Krüger projection is currently being replaced by the system ETRS89 with the ellipsoid GRS80 and the UTM projection.

The classical method of land surveying

The storage (definition ) of a reference ellipsoid is relative to the Earth's body by the latitude and longitude of the fundamental point determined astronomically, and with its ellipsoidal latitude / longitude is equated. Together with the exact direction to a remote triangulation becomes the rotational axis of the ellipsoid parallel to that of the real world. The center of the ellipsoid, however, does not coincide with the center of the earth, because the gravitational field of each region has certain irregularities (see geoid ). The center points can differ by some 100 meters - depending on the position of the fundamental point in the region and its geology.

This fact is advantage and disadvantage at the same time:

• An advantage is the better adaptation of a regional ellipsoid to the earth's curvature prevailing there, and thus a more accurate basis of land surveying,
• Adversely affect the difficult transition between neighboring states ( the coordinates of the boundary points differ by up to 500 m), and today the discrepancies to GPS fixes.

Fundamental points in Europe

Some fundamental points in Europe are:

• The Hermannskogel in Vienna (542 m above sea level. A. ) for the territories of Austria, Hungary, the former Czechoslovakia and Yugoslavia allowing individual country surveys, earlier also related to regional fundamental points such as Innsbruck, the Gusterberg at Kremsmuenster or the Graz Mountain Schoeckl.

The direction of decisive triangle side usually has a length of about 30 km; those of Austria - Hungary ( Hermannskogel - Hundsheimer Berg) was unusually long at 60 km chosen in order to increase the accuracy of the direction of very extensive network. The long to sight, the observation of which required a particularly good weather conditions runs, across the plane of the Vienna Basin.

In the 1920s, Germany, Austria and other states were transferred to the 3 ° - strip system of Gauss -Krüger projection, but play the previous fundamental points still play a role, for example in the analysis of survey networks and the digitalisation of older data of the cadastre. In the near future, the transition to a uniform EU 6 ° - reference system is carried out.

On the Puerta del Sol in Spain's capital, Madrid is the zero kilometer marker of the six main national roads of Spain, extending radially from there, via the Iberian Peninsula.

Gallery

Japan's fundamental point

Philippines fundamental point (right)

The Resurrection contains Russia's 0km

Spain's fundamental point