Unmanned aerial vehicle (UAV) photogrammetry is one of the most effective methods for capturing a terrain in smaller areas. Capturing a steep terrain is more complex than capturing a flat terrain. To ...fly a mission in steep rugged terrain, a ground control station with a terrain following mode is required, and a quality digital elevation model (DEM) of the terrain is needed. The methods and results of capturing such terrain were analyzed as part of the Belca rockfall surveys. In addition to the national digital terrain model (NDTM), two customized DEMs were developed to optimize the photogrammetric survey of the steep terrain with oblique images. Flight heights and slant distances between camera projection centers and terrain are analyzed in the article. Some issues were identified and discussed, namely the vertical images in steep slopes and the steady decrease of UAV heights above ground level (AGL) with the increase of height above take-off (ATO) at 6%-8% rate. To compensate for the latter issue, the custom DEMs and NDTM were tilted. Based on our experience, the proposed optimal method for capturing the steep terrain is a combination of vertical and oblique UAV images.
One of the main concerns of land administration in developed countries is to keep the cadastral system up to date. The goal of this research was to develop an approach to detect visible land ...boundaries and revise existing cadastral data using deep learning. The convolutional neural network (CNN), based on a modified architecture, was trained using the Berkeley segmentation data set 500 (BSDS500) available online. This dataset is known for edge and boundary detection. The model was tested in two rural areas in Slovenia. The results were evaluated using recall, precision, and the F1 score—as a more appropriate method for unbalanced classes. In terms of detection quality, balanced recall and precision resulted in F1 scores of 0.60 and 0.54 for Ponova vas and Odranci, respectively. With lower recall (completeness), the model was able to predict the boundaries with a precision (correctness) of 0.71 and 0.61. When the cadastral data were revised, the low values were interpreted to mean that the lower the recall, the greater the need to update the existing cadastral data. In the case of Ponova vas, the recall value was less than 0.1, which means that the boundaries did not overlap. In Odranci, 21% of the predicted and cadastral boundaries overlapped. Since the direction of the lines was not a problem, the low recall value (0.21) was mainly due to overly fragmented plots. Overall, the automatic methods are faster (once the model is trained) but less accurate than the manual methods. For a rapid revision of existing cadastral boundaries, an automatic approach is certainly desirable for many national mapping and cadastral agencies, especially in developed countries.
The main goal of our research was to design and implement an innovative target that would be suitable for accurately registering point clouds produced from unmanned aerial vehicle (UAV) images and ...terrestrial laser scans. Our new target is composed of three perpendicular planes that combine the properties of plane and volume targets. The new target enables the precise determination of reference target points in aerial and terrestrial point clouds. Different types of commonly used plane and volume targets as well as the new target were placed in an established test area in order to evaluate their performance. The targets were scanned from multiple scanner stations and surveyed with an unmanned aerial vehicle DJI Phantom 4 PRO at three different altitudes (20, 40, and 75 m). The reference data were measured with a Leica Nova MS50 MultiStation. Several registrations were performed, each time with a different target. The quality of these registrations was assessed on the check points. The results showed that the new target yielded the best results in all cases, which confirmed our initial expectations. The proposed new target is innovative and not difficult to create and use.
This paper presents classification methods that enable the division of space into homogeneous areas that combine the spatial characteristics with influence on land use and changes thereof. It was ...determined that the existing methods do not always include the criteria needed for the aggregation of spatial units into homogeneous groups. The results of the analysis showed that the identified homogenous groups do not fully capture the spatial complexity and diversity important for land use change analyses. For this reason, a new approach to the classification of spatial units based on the unsupervised classification of digital images was proposed. The methodology includes the selection of appropriate indicators, that consider land use more comprehensively and thus enable better classification results. The use of the unsupervised classification method for prevailing land use typology has been tested in Slovenia. At the municipal level, seven types of prevailing land use were identified.
In Ribčev Laz near Lake Bohinj there is a model of Triglav, the highest mountain in Slovenia. Made of stones, it is the work of the painter Valentin Hodnik from Bohinj. Although it is a work of art, ...we wanted to evaluate the correctness of its shape compared to the actual mountain. We photographed it and created a point cloud model using the Structure from Motion process (SfM). By transforming the point cloud to actual size, we were able to compare it with the actual shape of the Triglav mountain range obtained from Laser Scanning of Slovenia (LSS). As expected, the shape of the model varied considerably from the actual shape of the mountain, and the scale of the individual slopes and ridges was not the same. For a qualitative evaluation of the model, we calculated the distances between the transformed model and actual surface. The average absolute distance between the nearest points in both point clouds was 41.8 m (6 cm at a built-model scale) with a standard deviation of 38.0 m (5.4 cm). The results are represented by a picture of absolute distances. We also produced a smaller 3D print of the Triglav model and the actual shape of the mountain.
U Ribčevom Lazu kraj Bohinjskog jezera nalazi se maketa Triglava, najviše planine Slovenije, izgrađena od kamena, rad slikara Valentina Hodnika iz Bohinja. Iako je umjetničko djelo, odlučili smo procijeniti točnost njezinog oblika. U tu smo svrhu snimili maketu fotografskim aparatom i korištenjem procesa struktura iz kretanja (SfM) stvorili oblak točaka. Pretvarajući taj oblak točaka u stvarnu veličinu planine, uspoređivali smo oblik makete sa stvarnim oblikom planinarskog područja Triglava dobivenim iz podataka laserskog skeniranja Slovenije (LSS). Kao što se očekivalo, oblik makete značajno odstupa od stvarnog oblika planine, a ni mjerilo pojedinih padina i grebena nije isto. Za kvalitativnu procjenu makete izračunali smo udaljenosti između najbližih točaka transformiranog modela makete i stvarne površine. Prosječna udaljenost između najbližih točaka oba modela je 41,8 m (6 cm u mjerilu makete) sa standardnom devijacijom od 38,0 m (5,4 cm). Rezultati su prikazani s pomoću slike apsolutnih udaljenosti. Osim toga, izradili smo i umanjen 3D otisak makete Triglava i stvarnog oblika planine.
Speleogeneza je proces nastajanja, razvoja in izginjanja jam. Zaključni stadij razvoja jame imenujemo brezstropa jama. Proučevanje le-teh nam lahko pomaga pri razumevanju krasa in kraških pojavov. ...Ker so brezstrope jame ali kotanje na površju ali le zaplate nekraških sedimentov z bujnejšim rastjem, v članku preučujemo možnosti kabinetnega prepoznavanja teh pojavov na podlagi njihovih morfometričnih lastnosti in spektralnih lastnosti vegetacije, ki jih prerašča. Raziskava je osredotočena na širše območje Podgorskega krasa v jugozahodni Sloveniji.
The topic of this paper is the challenges of using remote sensing technologies as one of the potential data sources for the establishment of a 3D real property cadastre in Slovenia. More than a ...decade ago, the legal basis for the registration of property rights on the buildings and parts of buildings was provided in Slovenia, and for this purpose, the Building Cadastre was established. The analyses of the current data within the Land Cadastre and the Building Cadastre revealed that the 3D graphical representation of buildings, where the second level of detail (LoD 2) was discussed, requires additional data in which significant roof points should be additionally acquired. For this purpose, i.e. the creation of a graphical 3D-model of a building at the level LoD 2, we use the cadastral and national topographic data that covers the entire state territory, which are stereopairs of aerial photographs of the cyclic aerial survey (CAS) and airborne laser scanning data. Using a case study, we have analysed and discussed the appropriateness of the state airborne laser scanning data as an additional data source, along with the current cadastral data, for the creation of 3D-building model at the second level of detail, which is important from the cadastral as well as topographic perspective.
Extreme events such as flash floods and debris flows are frequent phenomena that occur in steep torrential catchments; these kinds of events can cause notable geomorphic changes. Repeated terrestrial ...laser scanning (TLS) surveys were performed in a steep forested catchment of the Kuzlovec torrent (drainage area ~0.7km2) in central Slovenia, where a ~200-m long section of the torrent was scanned in 2013, 2014, and 2015. The main aim of this study was to perform the geomorphic response detection in the torrent due to hydro-meteorological events of different magnitudes. After applying several pre-processing steps, digital terrain models (DTMs) with a cell resolution of 5cm were produced. The geomorphic change detection was performed using the DTM of Difference approach (DoD). Several above-average flow events occurred in the period from 2013 to 2015 (some of them can be regarded as floods). The 2014 August extreme flash flood that was initiated by the rainfall event with a return period exceeding 100years, where maximum 1-minute rainfall intensities were up to 288mm/h, led to erosion rates of an order of magnitude higher than average annual erosion rates. Moreover, the analysis of the geomorphic changes shows that the August 2014 flash flood caused intense sediment transport processes that resulted in the changes at the location of the main stream channel thalweg and reduced channel roughness. The unit stream power for the scanned section of the torrent was assessed to be approximately 500W/m2 during this extreme event. This is above the thresholds that were suggested to differentiate between the situations where significant geomorphic changes can occur and the situations where geomorphic changes are not notable.
•Repeated TLS surveys were performed to detect geomorphic changes.•The flash flood changed the geomorphic characteristics of the torrent channel.•Erosion rates due to the flash flood event were much higher than average annual rates.•High spatial resolution data are a useful tool to detect changes in steep forested torrents.
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