EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Integration of point clouds from UAV photogrammetry and laserscan survey for the assessment of the risk of collapse of the vault of an underground cavity

Davide Martinucci1, Simone Pillon1, Annelore Bezzi1, Giulia Casagrande1, Giorgio Fontolan1, Michele Potleca2, Fiorella Bieker2, Antonio Bratus2, Paolo Manca2, Rita Blanos3, and Paolo Paganini3
Davide Martinucci et al.
  • 1Università degli Studi di Trieste, Trieste, Italy (
  • 2Regione Autonoma Friuli Venezia Giulia, Trieste, Italy
  • 3Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Trieste, Italy

Photogrammetric surveys from UAV and LiDAR surveys are two techniques that allow for the production of very high resolution point clouds. The use of these techniques result in a detailed reconstruction of difficult-to-access environments such as underground cavities. A rigorous georeferencing of the acquired data allows for a comparison of the hypogean development of the cave to the overlying territory. This study presents a case of integration between these two techniques, applied to the risk assessment of the collapse of the vaults in a natural cavity in the Trieste Karst (north east Italy). This site is particularly delicate given that on the slope above the cave there is an abandoned stone quarry. In order to survey the quarry above the cave, a flight was performed with UAV, while the cave was surveyed with Laser Scan from the ground. The flight was made using a UAV DJI Phantom RTK, which carried a 20 Mpixel 1“ sensor camera. 8 ha of terrain was surveyed, capturing about 733 high resolution images and surveying 22 GCPs (Ground Control Point) with a GNSS RTK receiver. It was possible to reduce the number of GCPs, since the drone recorded the shooting positions very accurately with the on-board GPS RTK. Data were analyzed using Agisoft Metashape Professional to produce an orthophoto and a DSM (Digital Surface Model) with a ground resolution of 0.02 m and 0.04 m respectively. The point cloud has a density of 586 points/m2. The LiDaR survey was carried out using an ILRIS 3D ER laser scanner from Optec. The point cloud has a density of approximately 2500 points/m2 and 5 stations were needed to cover the underground development of the cavity. The georeferencing of the data was carried out by roto-translation on geo-referenced benchmarks, surveyed with GPS RTK and total station. The point cloud was processed using Terrascan software (Terrasolid). The two point clouds were aligned, geo-referenced and combined using Polyworks software (Innovmetric), in order to check the thicknesses of the material present above the vault of the cave. The integration of epigean and hypogean data made it possible to identify some critical points related to a vault thickness of approximately 1.5 meters, located at the quarry square. This work made it possible to highlight critical issues difficult to detect without the integrated approach of these different survey methodologies.

How to cite: Martinucci, D., Pillon, S., Bezzi, A., Casagrande, G., Fontolan, G., Potleca, M., Bieker, F., Bratus, A., Manca, P., Blanos, R., and Paganini, P.: Integration of point clouds from UAV photogrammetry and laserscan survey for the assessment of the risk of collapse of the vault of an underground cavity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7669,, 2020

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Presentation version 2 – uploaded on 27 Apr 2020
Fixed some minor translation errors
  • CC1: Comment on EGU2020-7669, Rafaela Niemann, 08 May 2020

    Dear Davide Martinucci, Your work is very interesting, and the union of point clouds resulted in a very nice job. I would like to know how vegetation was removed from the UAV-SFM point cloud, whether it was done by filtering on specific software or on the metashape itself. I have my reservations about the point clouds filtered by the metashape, as I always seek better solutions for sparse vegetation. Could we talk more about that? Thank you!

    • AC1: Reply to CC1, Davide Martinucci, 08 May 2020

      Dear Rafaela Niemann,
      thanks for your interest and for your question. 
      On the first time we tried to filter vegetation with Metashape tools but the results were not satisfactory and a major manual intervention was required.
      So we used TERRASCAN that is a great software for this things.

      • AC2: Reply to AC1, Davide Martinucci, 08 May 2020

        However, in this case, the critical area above the quarry was without vegetation (or with very low vegetation) and there is not much difference between the DSM and the DTM

Presentation version 1 – uploaded on 22 Apr 2020 , no comments