PyTrx: A Python toolbox for deriving velocities, surface areas and line measurements from oblique imagery in glacial environments

Abstract. Terrestrial time-lapse photogrammetry is a rapidly growing method for deriving measurements from glacial environments because it provides high spatio-temporal resolution records of change. However, glacial photogrammetry toolboxes are limited currently. Without prior knowledge in photogrammetry and computer coding, they are used primarily to calculate ice flow velocities or to serve as qualitative records. PyTrx (available at https://github.com/PennyHow/PyTrx) is presented here as a Python-alternative toolbox to widen the range of photogrammetry toolboxes on offer to the glaciology community. The toolbox holds core photogrammetric functions for point seeding, feature-tracking, image registration, and georectification (using a planar projective transformation model). In addition, PyTrx facilitates areal and line measurements, which can be detected from imagery using either an automated or manual approach. Examples of PyTrx's applications are demonstrated using time-lapse imagery from Kronebreen and Tunabreen, two tidewater glaciers in Svalbard. Products from these applications include ice flow velocities, surface areas of supraglacial lakes and meltwater plumes, and glacier terminus profiles.