Telescope position
With a theodolite or tacheometer one can target point into two positions of the telescope be targeted by the entire instrument (the alidade ) by 180 ° around the vertical axis rotated and then the telescope so tilted - "punctured" - is that again the same target sighted is .
Because the vertical circle changes its position from left to right (or vice versa), one also speaks of the second circular position (depending on the instrument: circular position left and right or circular position I and II).
Penetration with averaging is performed for the following reasons:
- The constructive tilt axis error (some 0.001 °) is completely eliminated when aiming in 2 circular positions
- The not completely gone adjusted rest of the line of sight error is eliminated
- The measurement accuracy increases (but also the effort): on the one hand by averaging both readings, on the other hand by reducing the observer's aiming error (only about 1 ", but systematic effect - see also personal equation )
- A possible eccentricity of the standing axis (a few µm ) is harmless (that of the tripod setup , however, remains effective)
literature
- Heribert Kahmen : Applied Geodesy. Surveying . 20th edition. DeGruyter, Berlin 2006, ISBN 3-11-018464-8 .
- Berthold Witte, Hubert Schmidt: Surveying and the basics of statistics for the construction industry . 6th edition. Wichmann, Heidelberg 2006, ISBN 3-87907-435-6 .