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The most important topics are:
- Establishment of geodetic datum systems (e.g. ED50) or at expeditions
- apparent places of stars, and their proper motions
- precise astronomical navigation
- astro-geodetic geoid determination
- modelling the rock densities of the topography and of geological layers in the subsurface
- Satellite geodesy using the background of stars
- Monitoring of the Earth rotation and polar wandering
- Contribution to the time system of physics and geosciences
Important measuring techniques are:
- Latitude and longitude determination by theodolites, tacheometers, astrolabes or zenith cameras
- time and star positions by observation of star transits, e.g. by meridian circles (visual, photographic or CCD)
- Azimuth measurements
- Vertical deflection measurements and their use
- Modern spatial methods
The accuracy of these methods depends on the instrument and its spectral wavelength, the measuring or scanning method, the time amount (versus economy), the atmospheric situation, the stability of the surface resp. the satellite, on mechanical and temperature effects to the instrument, on the experience and skill of the observer, and on the accuracy of the physical-mathematical models.
Therefore, the accuracy reaches from 60" (navigation, ~1 mile) to 0,001" and better (a few cm; satellites, VLBI), e.g.:
- angles (vertical deflections and azimuths) ±1" up to 0,1"
- geoid determination & height systems ca. 5 cm up to 0,2 cm
- astronomical lat/long and star positions ±1" up to 0,01"
- HIPPARCOS star positions ±0,001"
- VLBI quasar positions and Earth's rotation poles 0,001 to 0,0001" (cm...mm)
- Astronomy, stellar triangulation, spherical trigonometry
- Satellite, space techniques, electro-optics, CCD
- Triangulation, tacheometer, passage instrument
- Astro navigation, Karl Ramsayer
- Astrometry and cosmic triangulation
- Zenith camera