Second paper about photogrammetry and LiDAR:
TERRESTRIAL LASER SCANNING COMBINED WITH PHOTOGRAMMETRY FOR
DIGITAL OUTCROP MODELLING
S. J. Buckley, E. Schwarz, V. Terlaky, J. A. Howell, R. W. C. Arnott
"ABSTRACT:
The integration of 3D modelling techniques is often advantageous for obtaining the most complete and useful object coverage for many application areas. In this paper, terrestrial laser scanning and digital photogrammetry were combined for the purposes of modelling a geological outcrop at Castle Creek, British Columbia, Canada. The outcrop, covering approximately 2.5 km2, comprised a smooth, scoured surface where recent glacial retreat had left the underlying sedimentary rocks exposed. The outcrop was of geological interest as an analogue to existing hydrocarbon reservoirs, and detailed spatial data were required to be able to map stratigraphic surfaces in 3D over the extent of the exposure. Aerial photogrammetry was used to provide a 2.5D digital elevation model of the overall outcrop surface. However, because the sedimentary strata were vertically orientated, local vertical cliffs acted as cross-sections through the geology, and these were surveyed using a terrestrial laser scanner and calibrated digital camera. Digital elevation models (DEMs) created from both methods were registered and merged, with the fused model showing a higher fidelity to the true topographic surface than either input technique. The final model was texture mapped using both the aerial and terrestrial photographs, using a local triangle reassignment to ensure that the most suitable images were chosen for each facet. This photorealistic model formed the basis for digitising the geological surfaces in 3D and building up a full 3D geocellular volume using these surfaces as input constraints. Because of the high resolution and accuracy of the input datasets, and the efficacy of the merging method, it was possible to interpret and track subtle surface separations over the larger extents of the outcrop.
CONCLUSIONS
Terrestrial laser scanning and digital aerial photogrammetry were combined to create a digital elevation model of the Castle Creek outcrop, British Columbia, Canada. The integration of the two techniques proved to be essential to capture both the large outcrop surface and the near-vertical cliff sections which were essential for being able to recreate the 3D orientation of geological surfaces. Use of surface matching allowed the aerial photogrammetric DEM to be accurately registered, without the problems of collecting a conventional photocontrol point arrangement in a rugged and remote area. Texture mapping with aerial and terrestrial images resulted in a photorealistic model that could be used by geologists for interpretation, education and quantitative analysis. This model demonstrated the application of geomatics for geological outcrop analogue modelling, allowing the spatial accuracy and resolution to be enhanced. A geocellular volume was created from digitised features, which will be used by geologists to improve the geological understanding of the Castle Creek outcrop."
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