Use of UAS and TLS technology in 3D modeling of constructions with complex architecture

3D building models are widely used in many applications. The use of terrestrial laser scanning and UAS photogrammetry for 3D modelling is a popular practice especially for constructions with complex architecture. The present article presents an example of using these technologies successfully for 3D modelling of the Episcopal Cathedral of the Holy Trinity from Baia Mare, Romania.  A number of 51 control and verification points were determined by the closed circuit travel method and the intersection method. All measurements were processed in Terramodel software. The control points used in the georeferencing of the scans were materialized by metal stakes and the verification points were materialized by reflective targets. Depending on the construction configuration, the field of view and the minimum/maximum scanning distances were subsequently set. A total of 45 scans were performed to model the entire cathedral. The photogrammetric flight was performed in RTK mode, with corrections being transmitted from the DJI D-RTK-2 Mobile Station base to the RTK drone. All retrieved frames had geolocation and frame orientation elements recorded by the IMU module. A total number of 222 photograms were taken, as a result of a double grid photogrammetric flight, with the camera oriented at 60 degrees, but also as a result of manual acquisition by performing orbital flights at different heights: an orbital flight on the ground floor, an orbital flight at the level of about 40 meters and an orbital flight around the tower.