The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Arko Lucieer - One of the best experts on this subject based on the ideXlab platform.
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using an unmanned aerial vehicle uav to capture micro topography of antarctic moss beds
International Journal of Applied Earth Observation and Geoinformation, 2014Co-Authors: Arko Lucieer, Darren Turner, Diana H King, Sharon A RobinsonAbstract:Mosses, the dominant flora of East Antarctica, show evidence of drying in recent decades, likely due to the regional effects of climate change. Given the relatively small area that such moss beds occupy, new tools are needed to map and monitor these fragile ecosystems in sufficient detail. In this study, we collected low altitude aerial photography with a small multi-rotor Unmanned Aerial Vehicle (UAV). Structure from Motion (SfM) computer vision techniques were applied to derive ultra-high resolution 3D models from multi-view aerial photography. A 2 cm digital surface model (DSM) and 1 cm Orthophoto mosaic were derived from the 3D model and aerial photographs, respectively. The geometric accuracy of the Orthophoto and DSM was 4 cm. A weighted contributing upstream area was derived with the D-infinity algorithm, based on the DSM and a snow cover map derived from the Orthophoto. The contributing upstream area was used as a proxy for water availability from snowmelt, one of the key environmental drivers of moss health. A Monte Carlo simulation with 300 realisations was implemented to model the impact of error in the DSM on runoff direction. Significant correlations were found between these simulated water availability values and field measurements of moss health and water content. In the future ultra-high spatial resolution DSMs acquired with a UAV could thus be used to determine the impact of changing snow cover on the health and spatial distribution of polar vegetation non-destructively.
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Mapping landslide displacements using Structure from Motion (SfM) and image correlation of multi-temporal UAV photography
Progress in Physical Geography, 2014Co-Authors: Arko Lucieer, Steven M.de Jong, Darren TurnerAbstract:In this study, we present a flexible, cost-effective, and accurate method to monitor landslides using a small unmanned aerial vehicle (UAV) to collect aerial photography. In the first part, we apply a Structure from Motion (SfM) workflow to derive a 3D model of a landslide in southeast Tasmania from multi-view UAV\r\nphotography. The geometric accuracy of the 3D model and resulting DEMs and Orthophoto mosaics was tested with ground control points coordinated with geodetic GPS receivers. A horizontal accuracy of 7 cm and vertical accuracy of 6 cm was achieved. In the second part, two DEMs and Orthophoto mosaics acquired on 16 July 2011 and 10 November 2011 were compared to study landslide dynamics. The COSI-Corr image correlation technique was evaluated to quantify and map terrain displacements. The magnitude and direction of the displacement vectors derived from correlating two hillshaded DEM layers corresponded to a visual interpretation of landslide change. Results show that the algorithm can accurately map displacements of the toes, chunks of soil, and vegetation patches on top of the landslide, but is not capable of mapping the retreat of the main scarp. The conclusion is that UAV-based imagery in combination with 3D scene reconstruction and image correlation algorithms provide flexible and effective tools to map and monitor landslide dynamics.
Darren Turner - One of the best experts on this subject based on the ideXlab platform.
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using an unmanned aerial vehicle uav to capture micro topography of antarctic moss beds
International Journal of Applied Earth Observation and Geoinformation, 2014Co-Authors: Arko Lucieer, Darren Turner, Diana H King, Sharon A RobinsonAbstract:Mosses, the dominant flora of East Antarctica, show evidence of drying in recent decades, likely due to the regional effects of climate change. Given the relatively small area that such moss beds occupy, new tools are needed to map and monitor these fragile ecosystems in sufficient detail. In this study, we collected low altitude aerial photography with a small multi-rotor Unmanned Aerial Vehicle (UAV). Structure from Motion (SfM) computer vision techniques were applied to derive ultra-high resolution 3D models from multi-view aerial photography. A 2 cm digital surface model (DSM) and 1 cm Orthophoto mosaic were derived from the 3D model and aerial photographs, respectively. The geometric accuracy of the Orthophoto and DSM was 4 cm. A weighted contributing upstream area was derived with the D-infinity algorithm, based on the DSM and a snow cover map derived from the Orthophoto. The contributing upstream area was used as a proxy for water availability from snowmelt, one of the key environmental drivers of moss health. A Monte Carlo simulation with 300 realisations was implemented to model the impact of error in the DSM on runoff direction. Significant correlations were found between these simulated water availability values and field measurements of moss health and water content. In the future ultra-high spatial resolution DSMs acquired with a UAV could thus be used to determine the impact of changing snow cover on the health and spatial distribution of polar vegetation non-destructively.
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Mapping landslide displacements using Structure from Motion (SfM) and image correlation of multi-temporal UAV photography
Progress in Physical Geography, 2014Co-Authors: Arko Lucieer, Steven M.de Jong, Darren TurnerAbstract:In this study, we present a flexible, cost-effective, and accurate method to monitor landslides using a small unmanned aerial vehicle (UAV) to collect aerial photography. In the first part, we apply a Structure from Motion (SfM) workflow to derive a 3D model of a landslide in southeast Tasmania from multi-view UAV\r\nphotography. The geometric accuracy of the 3D model and resulting DEMs and Orthophoto mosaics was tested with ground control points coordinated with geodetic GPS receivers. A horizontal accuracy of 7 cm and vertical accuracy of 6 cm was achieved. In the second part, two DEMs and Orthophoto mosaics acquired on 16 July 2011 and 10 November 2011 were compared to study landslide dynamics. The COSI-Corr image correlation technique was evaluated to quantify and map terrain displacements. The magnitude and direction of the displacement vectors derived from correlating two hillshaded DEM layers corresponded to a visual interpretation of landslide change. Results show that the algorithm can accurately map displacements of the toes, chunks of soil, and vegetation patches on top of the landslide, but is not capable of mapping the retreat of the main scarp. The conclusion is that UAV-based imagery in combination with 3D scene reconstruction and image correlation algorithms provide flexible and effective tools to map and monitor landslide dynamics.
Sharon A Robinson - One of the best experts on this subject based on the ideXlab platform.
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using an unmanned aerial vehicle uav to capture micro topography of antarctic moss beds
International Journal of Applied Earth Observation and Geoinformation, 2014Co-Authors: Arko Lucieer, Darren Turner, Diana H King, Sharon A RobinsonAbstract:Mosses, the dominant flora of East Antarctica, show evidence of drying in recent decades, likely due to the regional effects of climate change. Given the relatively small area that such moss beds occupy, new tools are needed to map and monitor these fragile ecosystems in sufficient detail. In this study, we collected low altitude aerial photography with a small multi-rotor Unmanned Aerial Vehicle (UAV). Structure from Motion (SfM) computer vision techniques were applied to derive ultra-high resolution 3D models from multi-view aerial photography. A 2 cm digital surface model (DSM) and 1 cm Orthophoto mosaic were derived from the 3D model and aerial photographs, respectively. The geometric accuracy of the Orthophoto and DSM was 4 cm. A weighted contributing upstream area was derived with the D-infinity algorithm, based on the DSM and a snow cover map derived from the Orthophoto. The contributing upstream area was used as a proxy for water availability from snowmelt, one of the key environmental drivers of moss health. A Monte Carlo simulation with 300 realisations was implemented to model the impact of error in the DSM on runoff direction. Significant correlations were found between these simulated water availability values and field measurements of moss health and water content. In the future ultra-high spatial resolution DSMs acquired with a UAV could thus be used to determine the impact of changing snow cover on the health and spatial distribution of polar vegetation non-destructively.
Ayman Habib - One of the best experts on this subject based on the ideXlab platform.
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true Orthophoto generation from aerial frame images and lidar data an update
Remote Sensing, 2018Co-Authors: Hamid Gharibi, Ayman HabibAbstract:Image spectral and Light Detection and Ranging (LiDAR) positional information can be related through the Orthophoto generation process. Orthophotos have a uniform scale and represent all objects in their correct planimetric locations. However, Orthophotos generated using conventional methods suffer from an artifact known as the double-mapping effect that occurs in areas occluded by tall objects. The double-mapping problem can be resolved through the commonly known true Orthophoto generation procedure, in which an occlusion detection process is incorporated. This paper presents a review of occlusion detection methods, from which three techniques are compared and analyzed using experimental results. The paper also describes a framework for true Orthophoto production based on an angle-based occlusion detection method. To improve the performance of the angle-based technique, two modifications to this method are introduced. These modifications, which aim at resolving false visibilities reported within the angle-based occlusion detection process, are referred to as occlusion extension and radial section overlap. A weighted averaging approach is also proposed to mitigate the seamline effect and spectral dissimilarity that may appear in true Orthophoto mosaics. Moreover, true Orthophotos generated from high-resolution aerial images and high-density LiDAR data using the updated version of angle-based methodology are illustrated for two urban study areas. To investigate the potential of image matching techniques in producing true Orthophotos and point clouds, a comparison between the LiDAR-based and image-matching-based true Orthophotos and digital surface models (DSMs) for an urban study area is also presented in this paper. Among the investigated occlusion detection methods, the angle-based technique demonstrated a better performance in terms of output and running time. The LiDAR-based true Orthophotos and DSMs showed higher qualities compared to their image-matching-based counterparts which contain artifacts/noise along building edges.
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new methodologies for true Orthophoto generation
Photogrammetric Engineering and Remote Sensing, 2007Co-Authors: Ayman Habib, Euimyoung Kim, Changjae KimAbstract:Orthophoto production aims at the elimination of sensor tilt and terrain relief effects from captured perspective imagery. Uniform scale and the absence of relief displacement in Orthophotos make them an important component of GIS databases, where the user can directly determine geographic locations, measure distances, compute areas, and derive other useful information about the area in question. Differential rectification has been traditionally used for Orthophoto generation. For large scale imagery over urban areas, differential rectification produces serious artifacts in the form of double mapped areas at object space locations with sudden relief variations, e.g., in the vicinity of buildings. Such artifacts are removed through true Orthophoto generation methodologies which are based on the identification of occluded portions of the object space in the involved imagery. Existing methodologies suffer from several problems such as their sensitivity to the sampling interval of the digital surface model (DSM) as it relates to the ground sampling distance (GSD) of the imaging sensor. Moreover, current methodologies rely on the availability of a digital building model (DBM), which requires an additional and expensive pre-processing. This paper presents new methodologies for true Orthophoto generation while circumventing the problems associated with existing techniques. The feasibility and performance of the suggested techniques are verified through experimental results with simulated and real data.
Luigi Barazzetti - One of the best experts on this subject based on the ideXlab platform.
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uav based Orthophoto generation in urban area the basilica of santa maria di collemaggio in l aquila
International Conference on Computational Science and Its Applications, 2014Co-Authors: Luigi Barazzetti, Raffaella Brumana, Daniela Oreni, Mattia Previtali, F RoncoroniAbstract:This paper presents the photogrammetric pipeline behind the generation of the UAV-based Orthophoto of the Basilica of Santa Maria di Collemaggio (L’Aquila, Italy). The 2009 L’Aquila earthquake caused serious damage to the basilica and a restoration work is currently in progress. A part of the research carried out by the authors was the investigation of UAV technology in urban context for supporting the surveying phase carried out with modern techniques that include total station data, laser scans, and close-range photogrammetry. The image acquisition phase by means of an UAV platform is illustrated and discussed along with the implemented algorithms used to generate an Orthophoto with a flight over the whole basilica. We would like to prove that UAV technology has reached a significant level of maturity and image acquisition can be carried out in fully automated way. On the other hand, image processing software today available on the commercial market could be insufficient for accurate and detailed reconstructions. The implementation of ad-hoc algorithms is therefore mandatory to exploit the full potential and automate the photogrammetric processing workflow.
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true Orthophoto generation from uav images implementation of a combined photogrammetric and computer vision approach
ISPRS Annals of the Photogrammetry Remote Sensing and Spatial Information Sciences, 2014Co-Authors: Luigi Barazzetti, Raffaella Brumana, Daniela Oreni, Mattia Previtali, F RoncoroniAbstract:Abstract. This paper presents a photogrammetric methodology for true-Orthophoto generation with images acquired from UAV platforms. The method is an automated multistep workflow made up of three main parts: (i) image orientation through feature-based matching and collinearity equations / bundle block adjustment, (ii) dense matching with correlation techniques able to manage multiple images, and true-Orthophoto mapping for 3D model texturing. It allows automated data processing of sparse blocks of convergent images in order to obtain a final true-Orthophoto where problems such as self-occlusions, ghost effects, and multiple texture assignments are taken into consideration. The different algorithms are illustrated and discussed along with a real case study concerning the UAV flight over the Basilica di Santa Maria di Collemaggio in L'Aquila (Italy). The final result is a rigorous true-Orthophoto used to inspect the roof of the Basilica, which was seriously damaged by the earthquake in 2009.
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lidar digital building models for true Orthophoto generation
Applied Geomatics, 2010Co-Authors: Luigi Barazzetti, Maria Antonia Brovelli, L ValentiniAbstract:The importance of digital Orthophotos in spatial databases has increased in recent years, since they are an efficient, low-cost and, if properly managed, accurate product. Usually, the generation of Orthophotos is carried out using digital terrain models (DTMs); meaning without taking into account vegetation, buildings, and other attached and detached structures. This leads to low accuracies in urban areas, bringing distortions into the image. To avoid this unwanted effect, one must adopt a digital surface model (DSM), as proposed by Amhar et al. (Int Arch Photogrammetry Remote Sens 32(4):16-22, 1998). The method proposed in this paper allows for the creation of true Orthophotos by using a DSM to refine the representation of buildings. The pixel size of the DSM must be similar to that of the true Orthophoto in order to model the roof edges with sufficient accuracy. This paper presents a new method capable of correcting the roof displacement using an approach based on the integration of several products today available in public administrations, such as a geodatabase, DTMs/DSMs, and light detection and ranging (LiDAR) data. The method is based on a rigorous modelling of simple roofs starting from their 2D projection in the geodatabase, while information about their heights can be obtained using LiDAR data. For some selected simple roofs, automatic modelling can be carried out, in which a robust interpolation method, such as RANSAC, is used to model the pitches identified by a clustering procedure. For complex roofs, where creating a rigorous model in a fully automatic way is not possible, a procedure based on the thickening of a DSM is carried out.
