COMPUTERIZED CARTOGRAPHY CHARTS CRETACEOUS CREATURES: PHOTOGRAMMETRIC ICHNOLOGY AND INTERPRETATION AT TRACKSITES IN THE WESTERN US

The use of photogrammetry to gather detailed 3D surface data on ichnological features, such as dinosaur tracks and trackways, has increased dramatically. This is due in large part to the use of digital cameras and the availability of user friendly software processing, as well as the cost effective and non-invasive nature of data collection. However, the use of photogrammetry need not be limited to single tracks and trackways. It has proven to be an effective method to capture very detailed surface information on entire tracksites with large contiguous areas of exposure. By following basic principles of photogrammetric best practice; taking photos nadir to the surface, using a wide-angle lens, fixing the focus, overlapping in-strip photos by 66% and between-strip photos by 50%, adding crossing strips, and processing the photos in a software that supports robust camera calibration and error identification and reduction; it is possible for photogrammetric data to achieve a precision of 0.1 mm for areas covering 100’s of square meters. By following these best practices, accuracies may be reported with confidence. The outputs generated from the photogrammetric process are compatible with standard GIS software and include orthophotomosaics, color depth maps, and topographic maps with contour intervals as fine as 2 mm. As with any geologically based discipline, field observations and analyses are key to understanding ichnological features. The tracings, maps, and track measurements of trained ichnologists (vital to interpreting the complex sequence of events that took place in the distant past) can be easily integrated with the 3D digital product.

The Mill Canyon Dinosaur Tracksite (MCDT) north of Moab, UT is an excellent example of the integration of field and photogrammetric documentation. This Lower Cretaceous tracksite (administered by the BLM’s Moab Field Office) contains a diverse vertebrate ichnofauna with a minimum of 10 named ichnotaxa, including dinosaurian, crocodilian and bird tracks. An interpretive trail with raised boardwalk and informational signs help the visitor to navigate and understand this dynamic snapshot of life from the Early Cretaceous. The MCDT project is one of a number of large tracksite photogrammetric projects that have been completed worldwide using state-of-the-art techniques.