New method of recording and processing precise digital levelling data

A new method of recording and processing digital levelling data has been developed to reduce the loss of data due to poor measurements and to be able to compute meaningful standard deviations from the original data. Rather than record a single height difference per instrument set-up, four backsight measurements and four foresight measurements are taken and stored on board the instrument. In post-processing, the four height differences per set-up are accumulated separately along a section to give four one-way section height differences. A practical example demonstrated that the use of multiple height differences per one-way section greatly improves the precision of the adjusted elevations in a network adjustment. Also, the weighting of the observations according to the section-by-section precision of the measurements produces a more realistic precision of the adjusted elevations as the precision is not longer solely distance dependent.