Abstract
Digital photogrammetry (DP) represents one of the most used survey techniques in engineering geology. The availability of new high-resolution digital cameras and photogrammetry software has led to a step-change increase in the quality of engineering and structural geological data that can be collected. In particular, the introduction of the structure from motion methodology has led to a significant increase in the routine uses of photogrammetry in geological and engineering geological practice, making this method of survey easier and more attractive. Using structure from motion methods, the creation of photogrammetric 3D models is now easier and faster, however the use of ground control points to scale/geo-reference the models are still required. This often leads to the necessity of using total stations or Global Positioning System (GPS) for the acquisition of ground control points. Although the integrated use of digital photogrammetry and total station/GPS is now common practice, it is clear that this may not always be practical or economically convenient due to the increase in cost of the survey. To address these issues, this research proposes a new method of utilizing photogrammetry for the creation of georeferenced and scaled 3D models not requiring the use of total stations and GPS. The method is based on the use of an object of known geometry located on the outcrop during the survey. Targets located on such objects are used as ground control points and their coordinates are calculated using a simple geological compass and trigonometric formula or CAD 3D software. We present three different levels of survey using (i) a calibrated digital camera, (ii) a non-calibrated digital camera and (iii) two commercial smartphones. The data obtained using the proposed approach and the three levels of survey methods have been validated against a laser scanning (LS) point cloud. Through this validation we highlight the advantages and limitations of the proposed method, suggesting potential applications in engineering geology.
Highlights
In the last decade, the use of remote sensing techniques in engineering analyses of slopes has increased dramatically
When using the digital camera, the survey was conducted at a distance of ca 10 m with a ca 2.6 m long baseline
The proposed method has been rigorously validated against laser scanning (LS) data and showed a close agreement between the LS and digital photogrammetry (DP) data measurements
Summary
The use of remote sensing techniques in engineering analyses of slopes has increased dramatically. Laser scanning (LS) and digital photogrammetry (DP) techniques have been described by numerous authors [1,2,3,4,5,6]. LS is a very powerful survey technique which allows 3D models of slopes to be rapidly produced at high precision and in a small amount of time. The availability of full waveform instruments has made this technique even more attractive, with the possibility of using LS for long range surveys (up to 6000 m) and displacement monitoring. The availably of aerial platforms, for using this technique, such as helicopter, aircraft and unmanned aerial vehicle (UAV) has allowed the surveying of very high and inaccessible steep slopes at a high resolution. It is important to note that one of the main limitations of LS remains the high cost of the instrumentation
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