Appraising Reflectorless Total Station Instruments

Abstract

A number of retroreflectors of various types were used to appraise the performance of reflectorless total stations as exemplified by a Leica TCR-1102 total station. For this purpose, a carefully-established geodetic test line was measured using these retroretlectors. Grand-pooled root-mean-square errors were then computed and converted to accuracy values. The results show that smooth white ceramic and porcelain tiles gave accuracy values of the order of 7mm in 100m with linear fractional errors better than 1/13000. These were followed by smooth and rough wooden white surfaces where grand-pooled r.m.s.e. values of around 9.5mm were obtained (corresponding to fractional errors better than 1/8000). Next come the smooth black surfaces (ceramic and porcelain tiles and the wooden reflector) and the white-painted steel reflector with corresponding accuracy figures of around 10 mm and fractional error of around 1/7500. Intermediate accuracy figures (1 /3000 – 115000) were obtained with the concrete block, the white zinc sheet and the unpainted steel bracket. Markedly lower accuracy was obtained with the rest of the reflectors, namely, the rough black wooden surface and the brown mud sheet. It is clear then that the first two groups gave results better than or similar to those quoted by the manufacturer i.e. around ± 10 mm in 80 m. This range of accuracy is commensurate with a number of civil engineering and architectural surveys. Other retroretlectors gave markedly lower accuracy figures. However, even those low figures could serve the purpose of some applications where stringent measuring precision levels are not sought or are not of paramount importance.