Orientation (geodesy)

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As orientation in which it is Geodesy the orientation of a measurement network , a measuring instrument or a set of directional measurements according to the geographic or geodetic north direction , respectively. In photogrammetry, this is understood to mean those parameters that describe the orientation of the measuring camera in space ( external orientation ).

The term "orientation" or "orientate oneself" comes from the historical representation in which maps were often aligned with Jerusalem = up. Jerusalem was equated with the Orient. Orienting a map meant turning the map so that the Orient is on top.

Orientation of a survey network

The orientation of a surveying network is the subject of classic national surveying . It takes place i. General on the central point ( fundamental point ) of the network through an exact astronomical azimuth determination carried out over several nights to a neighboring point of the first order (distance approx. 30–60 km). If the network is larger, further azimuth measurements are carried out on some of these triangulation points (TP). If an astronomical length determination is also carried out at these points , the outwardly slowly increasing distortion, which in principle occurs in every network, can be kept within narrow limits (see Laplace point ).

Larger networks or network parts for national surveying are rarely created today, but their accuracy is improved by methods of satellite geodesy - especially with GPS . The positional accuracy increases for a typical federal state from about 2–5 cm to 1–2 cm, while the orientation hardly improves any more. On the other hand, such an effect occurs when the surveying networks of neighboring countries are merged.

Orientation of a measuring instrument

In contrast to networks, the orientation of a theodolite or a set of measurements carried out with it is not based on the meridian (astronomical north), but on the grid north . This is i. General determined by the Gauß-Krüger coordinate system, the terrestrial reference system most commonly used in surveying.

The reference direction of such measurements can be obtained either

  • through the so-called "connection" of the instrument location to the official control point field , which provides a surveying point that is permanently marketed in the ground or on buildings approximately every 300–1000 meters ,
  • or by a so-called long - term goal (church tower, observation tower, chimney, etc.) that is visible from afar and is also measured in the Gauß-Krüger system,
  • or in individual cases by a quick “astronomical orientation” using the solar azimuth or a surveying top . In order to get the reference to the grid north, the meridian convergence has to be attached to the result.

Orientation of a map

In order to transfer directions from a map to the terrain, the map must be oriented to the north . There are several methods for this, which are listed below according to their speed and accuracy:

  1. 1 minute, ± 30 °: towards the mossy side of the trees (approximately northwest )
  2. 2 minutes, ± 15 °: according to the closest environment - e.g. B. Direction of the distance traveled
  3. 2 minutes, ± 10 °: according to the position of the sun - e.g. B. with the clock (hour hand to the sun, south ≈ middle between 12 o'clock and hand)
  4. 5 minutes, ± 1 °: by aiming at 1–2 long-range targets - e.g. B. Localities , road or rail lines, mountain peaks
  5. 15 minutes, ± 0.1 °: with a measuring method - for example on a measuring table or with the azimuth of the sun .

literature

  • Wolfgang Torge : Geodesy (3rd edition), de Gruyter-Verlag, Berlin 2001
  • Walter Großmann : Geodetic calculations and images in the land survey , Konrad Wittwer Verlag, Stuttgart 1976
  • Friedrich Hopfner : Basics of Higher Geodesy , Springer-Verlag, Vienna 1949.

Individual evidence

  1. Günter Petrahn: Fundamentals of Surveying , Cornelsen, 5th edition, 2003, ISBN 978-3464433355
  2. ^ Erwin Reidinger : Medieval church planning in town and country from the point of view of structural archeology; Position, orientation and axis bend. In: Contributions to Medieval Archeology in Austria , Volume 21/2005, Vienna 2005, pp. 49–66, ISSN  1011-0062
  3. Erwin Reidinger: Passau, St. Stephan Cathedral 982: Achsknick = time mark . In: The Passau Cathedral of the Middle Ages , publications by the Institute for Cultural Area Research in East Bavaria and the neighboring regions of the University of Passau, Volume 60, Passau 2009, pp. 7–32, ISBN 978-3-932949-91-3 , ISSN  0479-6748