1,721,026 research outputs found
Spherical Photogrammetry as Rescue Documentation for The Reconstruction of some UNESCO Sites in Syria
No full textRicostruzione per fotogrammetria sferica del minareto abbattuto di Aleppo e delle mura della cittadell
THE USE OF STRUCTURE FROM MOTION TECHNOLOGIES FOR HIGH-RESOLUTION TERRAIN MODELLING ON HIGH ALTITUDE CATCHMENTS
Full text linkThe research project developed in this Thesis involves the application of close-range photogrammetry based on the Structure from Motion (SfM) approach that allows reconstructing the 3D point cloud of the photographed object from a sequence of overlapping images taken with a common digital camera. Thanks to the characteristics of high portability of the equipment, flexibility of the method to reconstruct surface at different scale with high resolution, low-cost, and ease of use also for not expertise during both acquisition and processing phase, the SfM-photogrammetry is becoming a valid alternative to the range-based technology for remote sensing and monitoring of dynamic natural environments. The aim of this research was to test and validate the capability of a ground photogrammetric survey to reconstruct a surface by dealing the main practical issues of a ground acquisition and by highlighting the main error sources which may be present within the field data. Furthermore, the feasibility of the SfM-photogrammetry approach for monitoring glacial and periglacial processes was tested in order to highlight the limitation and the potential of the method for these applications.
A total of four study sites were surveyed in order to validate the photogrammetric method. A depth investigation on the photo-based approach was carried out in a test field area where different image acquisition, georeferencing methods and processing were compared and evaluated. A terrestrial panorama images acquisition was proposed and tested in this work. This acquisition strategy provided advantages in comparison to a normal single frame acquisition by increasing the spatial coverage of the reconstructed surface and the number of overlapping images that ensure higher accuracy.
The potential and limits of the ground-based SfM-photogrammetry approach for monitoring glacial and periglacial processes were investigated in three different environments. For each of these study areas several tests concerning the quality of the obtained photogrammetric digital elevation models (DEMs) were performed. Different resolution and accuracy of the photogrammetric DEMs were obtained for the three case studies according to the different ground survey characteristics and survey object (i.e. extension and accessibility of the areas, camera-object distance, surface coverage, and camera resolution and geometry network). For the investigated areas, the main practical problems of the ground photogrammetric surveys that affected the SfM-photogrammetry results were: i) image quality determined by poor texture (i.e. snow and dark rock area with low contrast) and strong illumination variations during long time photos acquisition, ii) camera network geometry (i.e. high camera-object distance, poor overlapping images) and iii) distribution and accuracy of control measurements. However, the photogrammetric 3D model allowed us to estimate with good accuracy the glacial and periglacial processes respect to the reference data.
The investigation on the SfM-photogrammetry quality reconstruction allowed to have a complete view of the critical points and the potential of this method for multitemporal analysis in remote alpine area and thus to assess the applicability range for future realistic case scenarios
Comparative analysis of terrestrial laser scanner and photogrammetry for the mass balance calculation of Montasio Occidentale Glacier
No full textUse of terrestrial photogrammetry based on structure-from-motion for mass balance estimation of a small glacier in the Italian alps
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Monitoring Glacial and Periglacial Environments in the Ortles-Cevedale (Eastern Italian Alps) Using the Sfm-Mvs Approach
No full textSuitability of ground-based SfM-MVS for monitoring glacial and periglacial processes
Full text linkPhoto-based surface reconstruction is rapidly emerging as an alternative survey technique to lidar (light detection and ranging) in many fields of geoscience fostered by the recent development of computer vision algorithms such as structure from motion (SfM) and dense image matching such as multi-view stereo (MVS). The objectives of this work are to test the suitability of the ground-based SfM-MVS approach for calculating the geodetic mass balance of a 2.1km2 glacier and for detecting the surface displacement of a neighbouring active rock glacier located in the eastern Italian Alps. The photos were acquired in 2013 and 2014 using a digital consumer-grade camera during single-day field surveys. Airborne laser scanning (ALS, otherwise known as airborne lidar) data were used as benchmarks to estimate the accuracy of the photogrammetric digital elevation models (DEMs) and the reliability of the method. The SfM-MVS approach enabled the reconstruction of high-quality DEMs, which provided estimates of glacial and periglacial processes similar to those achievable using ALS. In stable bedrock areas outside the glacier, the mean and the standard deviation of the elevation difference between the SfM-MVS DEM and the ALS DEM was-0.42 ± 1.72 and 0.03 ± 0.74 m in 2013 and 2014, respectively. The overall pattern of elevation loss and gain on the glacier were similar with both methods, ranging between-5.53 and + 3.48 m. In the rock glacier area, the elevation difference between the SfM-MVS DEM and the ALS DEM was 0.02 ± 0.17 m. The SfM-MVS was able to reproduce the patterns and the magnitudes of displacement of the rock glacier observed by the ALS, ranging between 0.00 and 0.48 m per year. The use of natural targets as ground control points, the occurrence of shadowed and low-contrast areas, and in particular the suboptimal camera network geometry imposed by the morphology of the study area were the main factors affecting the accuracy of photogrammetric DEMs negatively. Technical improvements such as using an aerial platform and/or placing artificial targets could significantly improve the results but run the risk of being more demanding in terms of costs and logistics
Application of terrestrial photogrammetry for the mass balance calculation on Montasio Occidentale Glacier (Julian Alps, Italy)
No full textApplication of terrestrial photogrammetry for the mass balance calculation on Montasio Occidentale Glacier
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