Introduction

This user manual describes the functionalities of the ANDROMEDE software. The ANDROMEDE (ANalyse de Données et de Relevés Optiques pour la Mesure de Débit et l’Ecohydraulique) software is a video or image processing platform for measuring surface velocities of natural flows. It is based on methods developed at IMFT, on Tractrac, FlowVelotool and Opyflow software, and directly on methods available in OpenCV libraries.

The specificity of ANDROMEDE is to propose methods adapted to drone measurements, whether for stabilization, orthorectification from GPS data or the possibility to process images acquired in motion.

ANDROMEDE is an open source software whose development was funded by the French Office of Biodiversity (OFB) through a project of the OFB/IMFT/PPRIME ecohydraulic Research Team. The development team is composed of people from the Toulouse Institute of Fluid Mechanics and the MFEED transfer unit.

ANDROMEDE is dedicated to the study of the problems at the scale of the river, in particular those concerning the interaction between natural flows and ecosystems. Its main functionality is to provide surface velocity fields in order to describe currentologies or estimate flows. Applications include the study of the attractiveness of fish passage structures, the proper functioning of these structures or the rapid estimation of flood or low water flows. The knowledge of velocity fields over a spatial area allows the coupling of hydrodynamic data with biological models to characterize habitats or migration conditions.

Another specificity of ANDROMEDE is that it favors particle tracking or optical flow methods. Compared to other software based on PIV, it is expected that the processing will be faster, allowing for a better differentiation between current velocities and wave velocities or parasitic movements (reflections). The disadvantage is to make the use of tracers in the flow even more necessary.

The principle of particle tracking is to identify on the recorded images, a particular pattern on the surface that follows the flow (leaves, branches, voluntarily injected particles, etc). We then determine the displacement between 2 images. This distance divided by the time provides a displacement speed. The time is given by the acquisition frequency and the distance in meters is obtained by the geometrical transformations described below. The main objective of ANDROMEDE is to facilitate this image processing by proposing different algorithms that minimize the detection error on the image and therefore on the displacement. Each algorithm being a priori more efficient for a given type of acquisition, it has been chosen to propose them all to the user. The user will find in this manual recommendations concerning the most suitable method for his studied flow.