In this paper, we evaluated the results in terms of accuracy and coverage of the LiDAR-UAV system DJI Zenmuse L1 and Digital Aerial Photogrammetric system (DAP – UAV) DJI Zenmuse P1 in a forested area under leaf-off conditions on three sites with varying terrain ruggedness/tree type combinations. Detailed reference clouds were obtained using terrestrial scanning by Leica P40. Our results show that branches pose no problem to the accuracy of LiDAR-UAV and DAP-UAV derived terrain clouds. Elevation accuracies for photogrammetric data were even better than for LiDAR data – as low as 0.015 m on all sites. However, the LiDAR system provided better coverage, with almost full coverage at all sites, while the DAP-UAV coverage declined with the increasing density of branches (being worst in the young forest). In the very dense young forest (Site 1), the coverage by photogrammetrically extracted terrain cloud using high calculation quality and no filtering achieved 80.7% coverage, while LiDAR-UAV reached almost 100% coverage. The importance of the use of multiple (or last) returns when using LiDAR-UAV systems was demonstrated by the fact that on the site with the densest vegetation, only 11% of the ground points were represented by first returns.

Point clouds derived using structure from motion (SfM) algorithms from unmanned aerial vehicles (UAVs) are increasingly used in civil engineering practice. This includes areas such as (vegetated) rock outcrops or faces above linear constructions (e.g., railways) where accurate terrain identification, i.e., ground filtering, is highly difficult but, at the same time, important for safety management. In this paper, we evaluated the performance of standard geometrical ground filtering algorithms (a progressive morphological filter (PMF), a simple morphological filter (SMRF) or a cloth simulation filter (CSF)) and a structural filter, CANUPO (CAractérisation de NUages de POints), for ground identification in a point cloud derived by SfM from UAV imagery in such an area (a railway ledge and the adjacent rock face). The performance was evaluated both in the original position and after levelling the point cloud (its transformation into the horizontal plane). The poor results of geometrical filters (total errors of approximately 6–60% with PMF performing the worst) and a mediocre result of CANUPO (approximately 4%) led us to combine these complementary approaches, yielding total errors of 1.2% (CANUPO+SMRF) and 0.9% (CANUPO+CSF). This new technique could represent an excellent solution for ground filtering of high-density point clouds of such steep vegetated areas that can be well-used, for example, in civil engineering practice.

Keywords: Laser Scanning, Structure from Motion, Texture, Orthophoto, Orthoimage, Photogrammetry Terrestrial laser scanning technology is used for creation of building documentation and 3D building model from its emerging at the turn of the millennium. Photogrammetry has even longer tradition in this field. Both technologies have some technical limitations if they are used for creation of a façade or even an interior orthophoto, but combination of both technologies seems profitable. Laser scanning can be used for creation of an accurate 3D model and photogrammetry for consequent application of high quality colour information. Both technologies were used in synergy to create the building plans, 2D drawing documentation of facades and interior views and the orthophotos of St. Nicholas Baroque church in Prague. The case study is described in details in the paper.

In this article, the autonomous mapping airship (AMA) equipped with lidar along with its basic properties is introduced. Other methods and technologies using unmanned aerial vehicles (UAVs) or conventional aircraft are then compared to the AMA. Specifically automatic reconstruction from photographs acquired with fixed wing UAVs and lidar taken from conventional aircraft. Comparison of technologies was realized in the locality of a brown coal mine spoil heap. The size of the spoil heap interest part is about three square kilometres and it is covered with wind-blown vegetation (trees, grass, bush). We also measured about 100 height check points (HCPs) using real-time kinematic Global Navigation Satellite System technology for the purpose of accuracy analysis in the locality. One group of the HCPs were measured on the vegetation-free ground and the second group on ground with low vegetation (grass). Other properties of the methods used and the data acquired were also compared. The most important of these were data density, vegetation penetrability, speed of data collection, and economical aspects.

Currently, the creation of digital copies (digital twins) of various objects by remote sensing methods producing point clouds is becoming commonplace. This might be particularly important for the digital preservation of historical objects. Such clouds are typically primarily acquired as unordered sets of points with regular dense spacing, making the clouds huge in size, which causes such clouds to be difficult to process, store and share. The clouds are, therefore, usually diluted before use, typically through uniform dilution with a set spacing; such dilution can, however, lead to the loss of detail in the resulting cloud (washed-out edges and fine features). In this paper, we present an easy-to-use and computationally inexpensive progressive dilution method preserving detail in highly rugged/curved areas while significantly reducing the number of points in flat areas. This is done on the basis of a newly proposed characteristic T, which is based on the local scattering of the cloud (i.e., on the ruggedness of the local relief). The performance of this algorithm is demonstrated on datasets depicting parts of historic buildings of different characters. The results are evaluated on the basis of (a) root mean square deviation (RMSD) between the original and diluted clouds, (b) of visual evaluation of the differences and (c) of reduction in the point cloud size, demonstrating an excellent performance of the algorithm with a minimum loss of detail while significantly reducing the point clouds (approx. by 47–66% compared to the corresponding uniform dilution for individual datasets)