Preliminary Results of Georeferencing Accuracy Using Sphere Targets in Point Cloud Registration

This research examines the viability of georeferencing point clouds obtained from terrestrial laser scanning (TLS) with spherical targets. Ground-based laser scanning is a modern technology for collecting spatial data about a territory. It is particularly useful for documenting immovable cultural heritage sites, restoring construction documentation for old buildings and sites with complex geometry, 3D cadastral surveys, and creating digital twins and surrogates. To achieve these goals, precise equipment is required (ground-based laser scanners) is required to achieve these goals. The resulting point cloud is usually in the local coordinate system of the instrument. However, positioning the point cloud or the model obtained from it in space requires the application of methods for transformation into a global coordinate system, known as georeferencing. This is usually achieved by using special measurement marks, which are first measured with the scanner and then coordinated by measurements with a total station. This study provides a preliminary analysis of the use of spherical marks centered on points that are coordinated by measurements with a global navigation satellite system (GNSS) in net Real Time Kinematic (RTK) mode. Currently, this mode is the most widely used for measuring points from a working geodetic base when performing cadastral activities, due to the low cost of the service and the quick final result with an accuracy of 2 cm in plan and 5 cm in elevation. This error, combined with the high accuracy (< 1 mm) of spherical mark recognition by the laser scanning data processing software, creates challenges for the successful registration and georeferencing of data. Deviations from the vertical caused by the error of GNSS measurements in height positions are analysed, and recommendations are given to overcome this problem. Results from several real cultural heritage sites surveyed using this method are presented. Conclusions and recommendations about the precision of georeferencing point clouds are presented.