Levelling

When leveling the measurement of height differences between points is called. When geometric leveling the difference in height is read to a horizontally laid down leveling to leveling rods which are placed vertically on the measurement points. In trigonometric leveling the height differences of angle and distance measurements are calculated. When hydrostatic leveling a hose scale is used.

Levelling is the engineering application, such as to produce flat surfaces to set up machines or horizontally to determine the slope so that water can flow.

Thus, over large areas, a common reference level is given as a starting point for the local leveling, height points by leveling are linked together to form a network level of the national survey nationwide. This Nivellementsnetz consists of an open mesh very accurate levellings which are compressed by smaller networks of lower accuracy. This height can be determined in structures that range over large distances, such as railway lines, for sure.

The mean error of a leveling S0 for the German main level network 1992 ( DHHN92 ) is intended to per km double leveling not exceed the following values:

  • Nivellementsnetz 1st order S0 <1.0 mm
  • Nivellementsnetz 2nd order S0 <1.5 mm
  • Nivellementsnetz 3rd order S0 <3.0 mm

The geometric leveling

The level instrument is set at an arbitrary observation point between the measurement points and leveled. To rule out systematic effects as those of the rest of inclination of the target axis, the curvature and refraction, this same target distances are observed. At each measurement point a leveling rod is placed vertically. On the leveling a scale is attached so that the reading of the leveler bar division in gives the perpendicular distance of the point from the instrument horizon ( devices horizon) of the level. Is measured with an unchanged line-up of the level to another point, as are the difference between the two readings the height difference of the two points.

So that a difference in height over a larger distance, over larger differences in altitude or obstacles can be measured in the measurement section is divided. A section consists of the measurement from the known point to the new point each. The level instrument is set leveled between the two. That is, the vertical axis is horizontal and perpendicular with error-free device, the target axis.

The reading of the leveling staff on the known point is called retrospect, the reading on the new point is called foresight. The readings are subtracted Review minus the foresight to get the height difference. A positive difference in height means that the terrain rises in Nivellementrichtung, a negative is that the terrain drops. The height differences of all sections arrived at the destination point is added to obtain the height difference between the starting point and destination point.

When geometric leveling the metric distance of the point is measured from the devices horizon at the bar for the height determination. This is a geometric quantity. Thus, between two points no water flows, the potential of gravity on both points must be equal. However, the earth's gravity is a physical quantity. With increasing length of the Nivellementszuges therefore arise differences between the geometrically defined height and physical height. Therefore, it is possible that between dots of the same geometrical height but water flows.

With the same target distances only the curvature of the earth and the direction of gravity are determined by the leveling of leveling instrument considered, but not the magnitude of the acceleration due to gravity. In the national survey is therefore corrected the damage caused by geometric leveling heights based on gravity measurements.

The hydrostatic leveling

The hydrostatic leveling works on the principle of communicating vessels: Are containers filled with water at the lowest point connected by tubes, so it turns in all containers of the same water level a. For practical application, a transparent tube is free of bubbles almost completely filled with water. If the two ends of the hose kept approximately at the same height, so raises the water level to a two hose ends. When hydrostatic leveling with this tube level no line of sight between the measurement points must be made. Therefore it is well suited for measurements in buildings. For accurate reading, the Feinmesstechnik offers special attachment pieces (eg glass cylinder) with a corresponding reading device or electronic data collection. This is the hydrostatic leveling especially handy for the ongoing, computer-assisted remote monitoring of structural movements.

The hydrostatic leveling can bridge distances up to 20 km between the stations. Thus, for example, wide rivers can be bridged at Nivellementszügen. The accuracy is better than 0.02 mm. The overall accuracy is better than 1 mm for distances of several kilometers. In order to achieve such a high accuracy over long distances, but have effects such as temperature differences in the liquid are taken into account for the measurement.

The hydrostatic leveling was already known in antiquity. For the construction of the pyramids a grave system was established around the construction site. The water level in the ditch was the height reference surface for the building.

Trigonometric leveling

In trigonometric leveling is with surveying instruments ( theodolites, total station, and others) the zenith angle z, and slope distance s' measured at the measuring point. The difference in height is then easily approximated according to the geometric formula or calculated.

For target distances over 200 m is the curvature of the earth and the terrestrial refraction are taken into account.

Other methods for determining the amount

When the barometric determination of the difference in air pressure is measured and used to calculate the height difference.

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