Comparative study of accuracy in distance measurement using: Optical and digital levels

In this research, three levels: the optical levels NA2 and N3 from Leica and the digital level SDL30 from Sokkia were subjected to distance measurement accuracy test. A base line of length 100.000 m was first established and divided into 10 equal parts using geodetic means. This was then re-measured with each of the three test levels. The mean of the distance measured by each level was compared to the geodetically established length. The r.m.s.e. values for each distance measurement were computed as standard deviations from the mean. The results showed that the Leica N3 and NA2 optical levels were able to measure distances to an accuracy approaching 1/5000 and 1/4000, respectively, while the SDL30 digital level achieved a distance accuracy figure of 1/10,000. The SDL30, therefore, gave accuracy values in distance measurement exceeding most known tacheometric methods. The results also indicate that in the absence of distance measuring instruments, levels can be used to measure distances of 100 m range to an accuracy within 1:4000