# Leveling total station

The tachymeter level is a device for determining the position of points. This takes place either in a local ( local ) coordinate system or in the supra-regional, the secular system (in surveying in Germany and Austria it is the Gauß-Krüger coordinate system ). If a leveling device is provided with so-called Reichenbach 's distance lines and a horizontal circle , it is called a leveling total station. It is one of the classic surveying devices without electronic components.

Small vertical lines, the distance lines, are etched into the optics of the device above and below the target axis at the same distance. Due to the laws of optics , these distance lines form an angle of refraction outside the lens , the so-called parallactic angle . The leveling station is aligned with the measuring rod located in the target; the distance between two marks , projected onto the measuring stick (and now reversed) is read off. Using the mathematical laws of similarity , the horizontal distance to the measuring stick can be determined. ${\ displaystyle a \,}$

In order to increase the accuracy of the measurement, the distance from the center of the device above the point to be recorded to the starting point of the parallactic angle is determined . The focal length of the lens must also be known. In order to be able to calculate with the laws of similarity, the distance between the two distance lines on the lens is fundamental as a basic parameter. Since these devices do not yet have any program-controlled elements, the distances must be calculated by hand. To determine the distance after ${\ displaystyle c \,}$ ${\ displaystyle f \,}$${\ displaystyle p}$

(Distance) = (focal length) / (distance between the distance lines) (distance between the distance lines on the measuring rod) - (distance to the center of the device)

so

${\ displaystyle e = {\ frac {f} {p}} \ cdot ac}$

To simplify matters, the device manufacturers have ensured that the distance due to the reset of the lens is zero and the quotient results in a simple round value, usually 100. This simplifies the formula for the distance to ${\ displaystyle c}$${\ displaystyle f / p}$

${\ displaystyle e = 100 \ cdot a.}$

Since the reading of the millimeter information on the measuring stick can be quite imprecise, this results in only a decimeter accuracy for the distance and a centimeter accuracy for the height information. The device is therefore only suitable for simple positional mapping, for example for topographical mapping.