Photogrammetry in Engineering Geology: Tools, Methods and Applications
Engineering geologists generally are trained as geologists, and they commonly have a background focused on the geologic and environmental factors that affect engineering design and construction. Their expertise also requires knowledge in soil and rock mechanics, groundwater, and surface water hydrology. The role of an engineering geologist is to understand the complexities of natural phenomena and geologic materials, and to describe them in a way that is readily usable in an engineering project.
When an engineering geologist tries to understand the natural environment and the response of the natural environment to engineering activities, he/she needs to employ a variety of tools. Photogrammetry and Remote Sensing are amongst the most frequently used tools used by engineering geologists because these techniques readily provide low-cost and time dependent data for large and inaccessible areas. In recent years, the availability and importance of these techniques have increased due to rapid technological developments.
Photogrammetry and Remote Sensing is the art, science, and technology of obtaining reliable information from noncontact imaging and other sensor systems about the Earth and its environment, through recording, measuring, analyzing and visualisation. The imaging platforms in photogrammetry include terrestrial (close-range photogrammetry), unmanned aerial vehicles (UAVs), aeroplanes and satellites.
With recent developments in electro-optical technologies, the sensors range from low cost optical devices (for example, smartphone cameras) to satellite pushbroom cameras, Synthetic Aperture Radar (SAR), aerial (LiDAR) and terrestrial (TLS) laser scanners, thermal and hyperspectral cameras. This diversity in data collection methods and platforms, together with advancements in data processing and analysis algorithms, have broadened the application fields of photogrammetry by providing higher data density and resolution, and better modelling and visualisation methods.
In addition, availability of low cost and easy-to-use software has made it possible for many non-experts (non-photogrammetrists) to use the technology efficiently in their engineering and research projects such as optimum route and site selection, tunnel and dam construction, or mining processes.
A collection of research regarding current tools and methods, and state-of-the-art approaches for the use of photogrammetric techniques in engineering geology and geotechnical engineering would give insights to allow researchers to better appreciate and analyse the opportunities in this field. Papers on topics related to the main theme, “Photogrammetry in Engineering Geology: Tools, Methods and Applications,” such as those listed below.
. Representative case studies on the use of all types of photogrammetric methods in engineering geology and geotechnical engineering;
. Engineering geological applications of satellite sensor data, i.e. optical cameras with high, medium and low resolutions; radar data, low-earth-observation (LEO) and geostationary satellites, multispectral datasets;
. Methods and applications with hyperspectral imagery in engineering geology and geotechnical engineering projects;
. Photogrammetric algorithms for site characterization, modelling, quality control, metric and numerical analysis, data management and visualization in engineering geology;
. Processing methods for mono and stereo imagery, multi-sensor and multi-resolution data, 3D reconstruction, image classification and data mining, analysis of multi-temporal data, 3D change detection;
. Close-range photogrammetric applications with low cost cameras and terrestrial laser scanners for rock and soil slopes, tunnels, or large excavations;
. Aerial photogrammetric applications from UAVs or aeroplanes equipped with LiDAR or optical sensors;
. Production of digital elevation models from various sources by different photogrammetric approaches and their use in solving engineering geology problems;
. Production of practical but precise thematic maps such as susceptibility, hazard, suitability, excavability and so forth by low-cost photogrammetric techniques;
. Precise and low-cost monitoring methods of engineering structures such as deep excavations, high-slopes, tunnels, high-fills etc. during construction and post-construction stages.
From outcrop to geological models
The big advantage with photogrammetry it that the result will be a 3D model of the surface rather than a stack of photos. That 3D model can then be used directly for creating a 3D geological model. That is what we will demonstrate in this little article.
Assuming you managed to create or retrieve a 3D outcrop model from your area of interest, how can you use it for early stage geological models? First, you will need to be able to import it. For that, most photogrammetry software will allow you to export the outcrop as an OBJ file with associated MTL file and images.
All of those are needed to get the best effects. The OBJ contains the triangulated surface and points of the reconstructed outcrop. The MTL file describes the ‘material’ and references the images to project onto the triangulated surface. These images are not the original photos, but are texture images. Textures are widely used in 3D modeling to give the appearance of realistic structures and colors. At the moment of the writing GEOREKA can only handle a single texture image, but will be updated to handle multiple texture files.
Importing an OBJ with the associated MTL and images will show a triangulated surface that looks like a real-life representation of the outcrop
The use of photogrammetry for geologic mapping has benefited the geological mapping program in many ways. These techniques have resulted in a much higher level of detail and precision than can be achieved with other methods.
Using software designed for precise calculation of three-point problems, geologists can map or measure fault, bedding, and foliation planes more accurately, especially where exposures are poor or in areas that are difficult to reach in the field.
Nowadays geologic maps are compiled in stereo as digital files and using photogrammetry and ArcGIS nearly eliminates most duplication of effort. No longer do geologists redraw the map several times, thereby saving many hours of labor and reducing the potential of introducing errors.
Avery, E. T., 1968, Interpretation of Aerial Photographs, Second Edition: Burgess Publishing Company, 324 p.
McGlone, Chris, editor, 2004, Manual of Photogrammetry, Fifth Edition: American Society of Photogrammetry, 1168 p.
Raisz, Erwin, 1962, Principles of Cartography: McGraw-Hill, 315 p.