Photogrammetry in ichnology: 3D model generation, visualisation, and data extraction

3D digitisation of surfaces became a standard procedure in ichnology in recent years. 3D models allow not only for the digital preservation of vulnerable ichnological records, but also for the illustration, qualitative description, and quantitative analysis of the fossils. Here we discuss how to obtain photographs for photogrammetry, to generate, scale, and orient the models, and to extract visualisations, measurements, and coordinates for data analysis. Different visualisation approaches are discussed and compared, including widely used techniques such as orthophotos, height maps, and contour maps, as well as rarely used yet promising methods such as low-angled shaded reliefs, surface inclination plots, ambient occlusion, and radiance scaling. These techniques may filter or enhance different properties of the model surface such as colour information, elevation, edges and slopes, 3D morphology, and specific features such as convexities or concavities, and will often reveal additional detail. Furthermore, an approach is presented to automatically calculate trackway parameters based on coordinates collected from the model visualisations. All discussed steps can be performed with free and open-source software, and we provide detailed software instructions. We argue that digital ichnology, when combined with sedimentological data of the site, can be equally or more effective and comprehensive as traditional ichnological fieldwork.