Accuracy Tests of Vertical Component of RTK GNSS Measurements Corrected by a Laser System

The RTK GNSS method is commonly used in the 3D machine control systems. The RTK GNSS solution corrected by a laser level system (millimetre GNSS (mmGPS)) has been designed to improve the vertical accuracy of RTK GNSS positioning. The purpose of this study was to verify mmGPS technology in different situations. Test measurements in two test areas were carried out to evaluate the accuracy, working radius, and height zone of mmGPS.All results were compared with the heights from geometric levelling. It was found that the mmGPS system provides subcentimetre vertical accuracy within a 300 m working radius and ±5 m vertical zone from the laser level. Accuracy started to decrease from a distance of 300 m. Tests of mmGPS at height differences between 5–20 m produced large discrepancies of up to ±60 mm. In these conditions, the RTK GNSS solution without an assisting laser level performed much better.