Tacheometry

L-Tachymetrie

Mayer and Wiesmann Tachometer

Subtense Bar

Tacheometry (from Greek ταχύς, tachys, "swift" and μέτρον, metron, "measure") is a branch of surveying that involves the rapid measurement of distance, elevation, and direction. It is a method used in topographic surveying to determine the horizontal and vertical positions of points on the Earth's surface.

Principles of Tacheometry

Tacheometry relies on the use of a tacheometer, a type of theodolite that is equipped with a stadia diaphragm or a tacheometric lens. The primary principle involves the use of stadia lines to measure the distance between the instrument and a staff held at the point to be surveyed.

Stadia Method

The stadia method is the most common technique in tacheometry. It involves reading the intercepts on a graduated staff through the telescope of the tacheometer. The distance is calculated using the formula: \[ D = k \cdot s + C \] where:

• \( D \) is the distance from the instrument to the staff,
• \( k \) is the multiplying constant (stadia interval factor),
• \( s \) is the staff intercept (difference between the upper and lower stadia readings),
• \( C \) is the additive constant (instrument constant).

Tangential Method

In the tangential method, the distance is determined by measuring the angles subtended by a known length on the staff. This method is less common but useful in certain situations where the stadia method is not applicable.

Applications of Tacheometry

Tacheometry is widely used in topographic mapping, construction, and engineering surveys. It is particularly useful in rough or inaccessible terrain where traditional methods of distance measurement are impractical.

Advantages of Tacheometry

• Rapid data collection: Tacheometry allows for quick measurement of distances and elevations.
• Versatility: It can be used in various types of terrain and conditions.
• Cost-effective: Reduces the need for extensive ground control and additional equipment.

Related Pages

• Surveying
• Theodolite
• Topographic surveying
• Stadia diaphragm
• Engineering surveys

See Also

• Geodesy
• Cartography
• Remote sensing

References

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