Distance Between Two
    Points
 Pacing
 Chaining
 Temperature
 Standardisation
 Catenary
 Slope
 Tension
 Tachaeometry
 Stadia System
 Measurement of
    Tacheometric Constants
 Refraction and Curvature
 Theodolite
    Tachaeometry
 Field Tachaeometry
 Electronic Tachaeometry

Tacheometry

Introduction

This method of survey consists of using either a level, theodolite or specially constructed tacheometer to make cross hair intercept readings on a levelling staff. As the angle subtended by the crosshairs is known, the distance can be calculated.

Definition

Tacheometry is an optical solution to the measurement of distance. The word is derived from the Greek Tacns, meaning 'swift', and metrot, meaning 'a measure'. Present day methods of tacheometry can be classified in one of the following three groups. The last two groups will not be covered in these notes.

1. Stadia System: The theodolite is directed at the level staff and the distance is measured by reading the top and bottom stadia hairs on the telescope view. For further information about this process is provided in Theodolite Tacheometry

2. Electronic Tacheometry: Uses a total station which contains an EDM, able to read distance by reflecting off a prism.

3. Subtense Bar system: An accurate theodolite, reading to 1" of arc, is directed at a staff, two pointings being made and the small subtended angle measured.

4. Optical Wedge system: A special theodolite with a measuring device in front of the telescope s directed at a staff. One pointing of the instrument is required for each set of readings.