| Summary: | A Sokkia LP,3A automatic laser level was tested for the purpose of judging its capability for differential heighting as practiced in engineering surveying works. A test line was first established on flat ground using precise levelling. This was re-measured using the laser level. Two approaches were followed.In the first, several closed loops were levelled and the corresponding misclosures calculated and compared with known levelling standards. In the second, the elevations of the pegs on the test line were reestablished several times from instrument station at the start of the test line. The r.m.s.e. values of height measurement were then calculated for each peg. These were also compared with known levelling standards. The results showed that in the first approach, the test instrument was able to give misclosure values better than ±7 mm for level circuits up to 340 m in length. This is commensurate with the requirements for third order optical levelling. In the second approach, the r.m.s.e. of height measurement of pegs up to 150 m from instrument station is better than ±2 mm. This is within the order of requirements for third order optical levelling. Taking into account the fact that with the laser level observations can be carried out by one person only, it is concluded that the laser level could be effectively used in place of conventional optical levels in localized surveys concerned with preparation of construction sites, drainage works, inner-city road surveys etc. where only lower order accuracy is required.
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