Height control point
A geodetic fixed point is referred to as a height reference point (HFP) , which is used specifically as a starting point for height measurement (technical or precision leveling ).
Height control points must have a particularly high level of stability in the marking , as the accuracy requirement is 1 millimeter or less, i.e. around 5 times higher than for position control points . The points of the basic network are therefore attached to geo - or structurally stable locations, such as B. on massive buildings that have existed for a long time and are no longer subject to settlement . At the particularly important points of the zeroth order ( reference points of the basic network), the markings are only set up on natural rock and after prior geological investigation.
Height control points were generally created by linear measurement, but are also networked with one another by means of compensation calculations. Their heights relate to the height system of the respective national survey (height above sea level , above the Adriatic Sea , above the Genoa gauge , etc.) or a regional date point . They are usually specified with an accuracy of 1 millimeter.
The main types of stabilization are
- Survey stone
- Tower bolts and other height bolts on buildings
- Cross mark or similar in the adjacent rock .
The height mark must have a clearly visible highest point on which the leveling staff is placed.
Height control points are periodically checked and monitored with regard to changes in height , which can also provide information about geodynamic changes in the earth's crust .
A selection of particularly stable HFPs (approximately every 50 km) also form the reference points of the gravity network .
literature
- Heribert Kahmen : Surveyors. Chapters 9–11 and 19. Gruyter textbook, Berlin 1997.
- Bernhard Heck: Calculation methods and evaluation models for national surveying. 3. Edition. Chapters 9 and 10; Wichmann-Verlag, Karlsruhe 2003.