Stadia Tacheometry with Electronic Theodolites

Abstract

Six simple electronic digital theodolites, three Sokkia instruments, a DT6, a DT5 and a DT2, a Topon DT20, a Zeiss ETh4 and a Leica T1600, were used to test measurement accuracy of horizontal distance and difference in elevation using stadia hairs etched on the telescope reticule of these new types of theodolite. A geodetic test line was remeasured using these theodolites and standard deviations in horizontal distance and differences in elevation were then computed using first, the nominal values of scale factor K and additive constant C (namely 100 and 0 respectively) and secondly, the least squares-computed counterparts of these two parameters. In the first case, horizontal distance accuracy obtained ranged from ± 10mm in 100m with the Leica theodolite to ± 16mm in 100m with the Sokkia DT6 instrument. The vertical distance accuracy ranged from ± 9mm (in 100m) with the Leica T1600 to ± 15mm (in 100m) with the Topcon DT-20 theodolite. The corresponding values in the second case were ± 8mm to ± 13mm in the horizontal direction and ± 7mm to ± 14mm in height.This means that in both cases, “semi-electronic tacheometry” gives accuracy figures much better (two to three times) than conventional optical stadia techniques. These high accuracy figures are believed to be attributed partially to repeated measurements and partially to the improved design of modern electronic theodolites used in the test. This range of accuracy figures is commensurate with the requirements of a number of surveying, civil engineering, agricultural, environmental and other localized-type surveys where only modest to moderate positional accuracy figures are sought.