Fixed point field
A location control point field is one of the bases for land surveys and cartography . The location fixed point fields are based on the measurement of spacious triangles, from which a step-by-step condensed surveying network is created through trigonometric calculations .
In today's industrialized countries , such networks were usually measured as early as the 18th and 19th centuries. As the central point of these land surveys, a conveniently located fundamental point was chosen , on which astronomers measured the exact geographical latitude (often also the longitude ) and one or two azimuths (directions) to distant network points. For Prussia this was z. B. the central point Rauenberg in Berlin, for Austria-Hungary the Hermannskogel near Vienna.
Classic principle of point determination
The fixed points result from a triangular network , the configuration of which was determined exclusively by angle measurement . Measuring devices were universal instruments and triangulation theodolites . The network scale was derived from a baseline (baseline or “base”) several kilometers long and measured with millimeter precision .
The trigonometric points (TP), which are about 5 km apart, were locally condensed by further measurement points to point spacings of about 1 km or in urban areas by means of photogrammetry even to 300 to 500 meters ( switch-on points ). The boundary and detailed measurements were connected to these measuring points, the directions related to clearly visible distant points (churches, radio masts, etc.).
Newer methods
From the 1960s, electronic distance measurement (EDM) was also used, which soon achieved centimeter accuracy over many kilometers. From around 1970, methods of satellite geodesy were added to the first-order network (point spacings of around 30 km) .
Today's benchmark fields must not be so closely, as with GPS -Theodoliten and modern total stations have to be bridged rapidly km distances 1 to 2
See also
literature
- Heribert Kahmen : Surveying , Chapters 6, 8 and 19. Gruyter textbook, Berlin 1997
- Karl Ledersteger : Astronomical and Physical Geodesy ( Earth Measurement ) , Chapters III and XIII. Jordan-Eggert-Kneissl Volume V, Handbook of Surveying, Verlag JB Metzler, Stuttgart 1969
- Bernhard Heck: Calculation methods and evaluation models for land surveying , 3rd edition, Wichmann-Verlag, Karlsruhe 2003