Heighting and Distance Accuracy with Electronic Digital Levels

Abstract

A Leica NA3000 electronic digital level, one of the newly-introduced heighting equipment, was evaluated for vertical and horizontal distance measurement. A well protected 170 m long 17-section test line was first established for this purpose using geodetic surveying techniques. The test instrument was then used to remeasure the line. Two approaches were followed. In the first, closed loops were run from one end of the line to each of the pegs on the line and back to the starting point in an out-and-back manner. Misclosure errors of loops were then computed and compared to known levelling standards. In the second approach, heights of some pegs on the line were re-established several times with the instrument erected on the one end of the line. Standard deviations of height measurement of each peg were then computed and compared with known standards. The results showed that in the first approach, the test instrument was able to achieve accuracy values commensurate with first order class I levelling standards as set out by the U.S.A.-based Federal Geodetic Control Committee (FGCC), i.e. better than ±3.0k mm. In the second approach, for distances up to 64 m, standard deviations better than ± 60 microns could easily be obtained. Again, this is within the requirements of first order class I levelling standards. Overall, therefore, it can be said that digital electronic levels, as exemplified by the Leica NA3000 model, could be used to support high accuracy levelling operations being them of the geodetic or ordinary type.The distance measuring stage of the test showed that, for up to 64 m from instrument station, the test instrument is capable of measuring distances to accuracy values better than 1/2000. This is sufficient accuracy for some localized survey works, e. g. site preparation in construction industry, pavement maintenance surveys, sewer pipe placement and monitoring etc. where distance errors of a few centimeters in several tens of meters are tolerable.