geodesy

from Wikipedia, the free encyclopedia

The Geodesy ( ancient Greek γῆ gé 'earth' and δαΐζειν daïzein , share ') is as defined by Friedrich Robert Helmert (1843-1917, founder of theoretical geodesy) and DIN 18709-1, the "science of measurement and representation of the earth's surface ". This includes the determination of the geometrical figure of the earth , its gravity field and the orientation of the earth in space.

In the scientific system, geodesy is primarily assigned to the engineering sciences . This is particularly clear at universities and technical colleges, where geodesy studies are often not assigned to the field of natural sciences but to civil engineering . Furthermore, geodesy represents the link between astronomy and geophysics . The expert in geodesy is the geodesist or geometer.

In mathematics , the term geodetic is used for the theoretically shortest connection between two points on curved surfaces - the geodetic line , which corresponds to an orthodrome on the globe .

Title page of a book on land surveying from 1616

structure

Geodesy was divided into two areas until around 1930:

The Ingenieurgeodäsie used both areas depending on the required accuracy of methods.

Around 1950, aerial photography was established as a separate subject under the name of photogrammetry  - since the 1990s, it has mostly been seen as a dual subject with remote sensing . Satellite geodesy began in 1958 .

The databases of the state or cadastral surveying developed into geographic information systems (GIS) or land information systems (LIS).

However, all of these sub-subjects are usually combined in a university course that also includes cartography or at least parts of it as well as a number of other major and minor subjects (e.g. land management ) and leads to the occupation of surveying engineer or geoinformatics specialist (see also geomatics or geomatics) . Geomatic engineer ). In North America (and the English specialist literature), however, a distinction is made between geodesy and surveying , which are hardly related in the curricula there. The designation Surveying corresponds to our word survey .

These specialists, who are academically trained in Europe, are often active in property valuation , construction, IT , cartography, navigation and spatial information systems in addition to the tasks listed above , while  other training courses predominate in the real estate industry  - with the exception of the land registry . The publicly appointed surveyors ( ÖbVIs ), called civil engineers in Austria , have the right to work in technical areas of geophysics in addition to real estate management.

Basics and sub-areas

With its survey results (e.g. from cadastral and national surveys , engineering geodesy, photogrammetry and remote sensing), geodesy provides the basis for numerous other specialist areas and activities:

The anomalies of the earth's gravity field at sea level (1 mgal ≈ 1 millionth of gravity). They are used to determine the exact shape of the earth ( geoid ) and the structure of the earth's crust.

The so-called higher geodesy ( mathematical geodesy , earth measurement and physical geodesy ) deals, among other things, with the mathematical earth figure , precise reference systems and the determination of geoid and earth's gravitational field. Various measurement methods are used to determine geoid: gravimetry , geometric and dynamic methods of satellite geodesy and astrogeodesy . Knowledge of the severity is necessary in order to establish an exact height system , for example with regard to the North Sea (so-called NN heights, see also Amsterdam level ) or the Adriatic Sea . The official height system in Germany is embodied in the German Main Height Network (DHHN).

The geoid (or its gradient, the deviation from the perpendicular ) also serves to define and reduce large-scale measurements and coordinates on the earth's surface. For triangulation and for longer connecting lines, the sea level is approximated using a reference ellipsoid and calculated using geodetic lines , which are also used in mathematics ( differential geometry ), navigation and when spanning light vaults ( geodetic dome ). Geoid and gravitational field are also important for applied geophysics and for calculating satellite orbits.

The higher geodesy area is also to be assigned to that area of ​​national surveying that deals with regional surveys and their reference systems . These tasks were previously solved terrestrially , but now increasingly with GPS and other satellite methods.

The so-called lower geodesy includes the recording of site plans for construction planning , documentation and creation of digital models for technical projects, the topographical recording of the site , the cadastral survey and areas of facility management .

If the ownership structure of the land has become more complicated over the course of time (through division when buying and selling or inheritance), then a so-called zoning becomes necessary. Their most important instrument is land consolidation , known in Austria as amelioration . It also serves to distribute loads evenly when areas have to be raised for large projects ( motorways , new construction routes ) (company land consolidation ).

With Ingenieurvermessung is referred to the technical (z. B. Gebäudeabsteckungen, Ingenieurnivellements, means of large machines, etc.), not Surveying

When performing geodetic tasks in underground - and also surface mining , one speaks of mine separation or mountain surveying.

The special fields of geodesy also include marine geodesy , sea ​​surveying and recording of hydrographic profiles of rivers , oceanographic altimetry with satellites and cooperation in the field of navigation .

A distinction is also made between the sub-areas of surveying technology as a technical part (instrument science) and the non-technical part of surveying as a collective term for the areas of higher and lower geodesy. The cadastre and real estate system is not part of surveying technology, although German courts such as the Düsseldorf Higher Regional Court (OLG) assume it in decision I-10 W 62/06 contrary to the doctrinal opinion prevailing at German colleges and universities.

history

Antiquity and the Middle Ages

The origin of geodesy in need, country divide, land and property boundaries to define and borders to be documented. Its history goes back to the " hydraulic society " of ancient Egypt , where the profession of geodesist became the most important in the country for a few weeks every year after the Nile flooded .

Man has always dealt with the stars and especially with the shape of the earth. At first it was assumed that the earth was a disk surrounded by the ocean. Pythagoras of Samos (around 500 BC) declared that the earth was a sphere, but he could not prove his thesis. This was not achieved until Aristotle (around 350 BC). He proved the thesis with the following three practical examples:

  1. Only a ball can cast a round shadow on the moon during a lunar eclipse.
  2. When traveling in a north-south direction, the appearance of new stars can only be explained by the spherical shape of the earth.
  3. All falling objects strive for a common center, namely the center of the earth.

The measurement of degrees by the Hellenistic scholar Eratosthenes between Alexandria and Syene (today's Aswan) around 240 BC was remarkable . Chr. It showed the earth's circumference at 252,000 stadia what (5000 stadiums estimate) came close to the true value despite the uncertain distance to about ten percent. The scientist and Alexandrian library director estimated the circumference of the earth from the 7.2 degrees different position of the sun .

As in Egypt, the surveying achievements of the Maya were astonishing, where geodesy was apparently strongly related to astronomy and calendar calculation .

Difficult tunnel measurements are also from the 1st millennium BC. Passed down, such as in the 6th century BC. The tunnel of Eupalinos on Samos .

Important milestones of ancient geodesy were the first world maps from Greece, the observatories in the Middle East and various measuring instruments at some centers in the eastern Mediterranean . In 1023, Abu Reyhan Biruni  - a polymath of the Islamic world at the time - determined the radius of the globe on the bank of the Kabul River, then called the Indus, with a new measuring method he had invented, almost exactly at 6339.6 kilometers (the radius at the earth's equator is actually 6378 , 1 kilometer). At that time, in the 11th century Arabia, the construction of sundials and astrolabes was pushed to its peak, something that European scientists like Peuerbach could build on from 1300 onwards.

Modern times

Lithography stones in the archive of the Bavarian State Office for Surveying and Geoinformation

With the dawn of the modern era , the needs of cartography and navigation provided a renewed boost in development , for example in clock and device production in Nuremberg or the measurement and calculation methods used by Portuguese seafarers . The discovery of the angular functions (India and Vienna) and triangulation (Snellius around 1615) also fell into this epoch . New measuring instruments such as the measuring table (Prätorius, Nuremberg 1590), the "pantometrum" of the Jesuit Athanasius Kircher and the telescope / microscope enabled geodesy to carry out the first really precise land surveys by Jean Picard and others. a.

From around 1700 onwards, the maps improved again through exact calculation methods ( mathematical geodesy ). With the measurement of the degree along the Paris meridian by Jean-Dominique Cassini , his son Jacques Cassini and others, the large-scale earth measurement began , which reached its first climax in 1740 with the determination of the ellipsoidal earth radii by the French Bouguer and Maupertuis . The Cassinis measured the whole of France geodetically and thus laid the basis for the creation of the Carte de Cassini by César François Cassini de Thury and Jean Dominique Comte de Cassini . This was followed by the English-French trigonometric survey and then the trigonometric survey of Great Britain and Ireland .

In order to be able to combine the results of various projects and national surveys better, Roger Joseph Boscovich , Carl Friedrich Gauß and others gradually developed the equalization calculation , which since around 1850 has also benefited the establishment of precise reference systems and the measurement of space ( cosmic geodesy ).

The most important stations for geodesy in the 19th and 20th centuries were:

Results of geodetic work

Measuring instruments, devices and equipment

Important measuring instruments and devices

(Note: Surveyors tend to speak of instruments, but photogrammetry of devices.)

  • Tape measure and plumb line (measurement of horizontal distances)
  • Angle prism and range pole (measurement of alignments and right angles)
  • Theodolite (measurement of horizontal directions and vertical angles)
  • Total station (measurement of horizontal directions and vertical angles as well as spatial distances)
  • Level (measurement of height differences)
  • Gravimeter (measurement of the acceleration due to gravity)
  • GNSS receiver ( GPS , GLONASS , BeiDou or Galileo receiver ) (measurement of spatial distances to several satellite positions)
  • Laser scanner (automatic measurement of polar elements, two deflection angles and a spatial distance, to surfaces in the vicinity)
  • Measuring chamber ( photogrammetry ) (measurement of reflected radiation - photos, images)

Special and auxiliary equipment

Historical devices of antiquity

Historic devices of the modern age

Measurement and calculation methods

Measurement method in detail (alphabetical)

Calculation methods and calculation tools

Reference systems

Organizations

National

International

Important geodesics

Events

literature

Web links

Commons : Geodesy  - collection of images, videos and audio files
Wikibooks: Several books on the subject of earth sciences  - learning and teaching materials
Wiktionary: Geodesy  - explanations of meanings, word origins, synonyms, translations
  • Geodesy . In: Meyers Konversations-Lexikon . 4th edition. Volume 7, Verlag des Bibliographisches Institut, Leipzig / Vienna 1885–1892, p. 124.
  • Workplace Earth A generally understandable introduction to geodesy and surveying, supervised by all the relevant professional geodetic associations in Germany