Abstract
Abstract. Open pit mines localized in high mountains are probably one of the most complex environments for Structure-From-Motion (SfM) based photogrammetry. The case study presented in this paper refers to the realization of a detailed topographic mapping in the Torano marble basin (Apuan Alps, Italy) which needed, after decades of excavation activity, a new topographic survey.Given the requested very high resolution, the time constraints and safety-related problems, a photogrammetric approach by a fixedwing Unmanned Aerial Vehicle (UAV) was chosen to carry out thesurvey of the basin. In addition, given the morphological complexity of the area, characterized by extreme steep slopes more than hundreds of meters high, and the necessity to minimize the fieldwork without sacrificing the work quality, an UAV equipped with a L1/L2 Network Real Time Kinematic (NRTK) Global Navigation Satellite System (GNSS) was used.The scope of this work is to compare the accuracy of UAV derived 3D photogrammetric models realized with different approaches: by using traditional Ground Control Points (GCPs), by using the on-board Network Real Time Kinematic system for camera position detection, and a mix of both. At the end, we tested the quality of the models to verify the reachable levels of accuracy.
Highlights
Given the morphological complexity of the area, characterized by extreme steep slopes more than hundreds of meters high, and the necessity to minimize the fieldwork without sacrificing the work quality, an Unmanned Aerial Vehicle (UAV) equipped with a L1/L2 Network Real Time Kinematic (NRTK) Global Navigation Satellite System (GNSS) was used
The high accuracy camera positions stored in the exif metadata format, allowed completing the alignment phase of the SfM process of 2071 images in 2 hours with a Dual Xeon Workstation, 128 Gigabyte RAM and 2 GPU
The relevant information for this work are the differences between the coordinates measured from the obtained block model and the real coordinates measured in the field trough the GNSS topographic survey
Summary
This paper analyses the accuracy of a bundle-adjustment photogrammetric process which uses photos from fixed-wing UAV flights over a morphological very complex mountain area. The new topographic map was created from: a) the extraction of contour lines from the dense 3D point cloud, b) the editing of contour lines within a 3D GIS environment, c) the drawing in 3D of the remaining topographic features basing on the interpretation of the orthophotomosaic. The dense point cloud and the orthophotomosaic, were generated by processing the digital images acquired by UAV flights and their bundleadjustment (topic of this work). As base for the new topography, the dense point cloud and the high resolution orthophotomosaic were used as described in papers from Mancini et al (2013), Gonçalves and Henriques (2015) and Westoby at al. The analysis of the final model spatial accuracy was carried out by using different approaches
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