Tacheometry in Survey Engineering

Tacheometry or quick measurement is a method that has intrigued the survey engineer throughout history. One scheme of method classification is as follows: (1) tangential; (2) fixed base; (3) optical reading reticule; (4) double image; and (5) short range electronic instruments. Of particular interest is the current tacheometers produced by firms such as Wild, Kern, and Zeiss. These instruments outperform stadia and can, within accuracies of about 1/500, lead to true quick measurement. In the higher accuracy range of 1/10,000 or better and to a distance of 2 km, the recent introduction of a gallium arsinide electronic measuring device by Tellurometer, Wild, Hewlitt-Packard, and several other companies has effectively limited the classical subtense bar and double image instruments to a few special purpose jobs. In all cases, the real consideration is the needed accuracy and the limitations on this accuracy by atmospheric and instrumental aberrations.