PaIRS-UniNa: a user-friendly free tool for particle image velocimetry and optical camera calibration

This contribution presents PaIRS-UniNa (Particle Image Reconstruction Software, University of Naples “Federico II”), a free software application developed since 2000 with the aim of providing fast and efficient tools for digital Particle Image Velocimetry (PIV) analysis in both research and industrial scenarios. PaIRS-UniNa relies on a powerful C library designed for speed, robustness and accuracy, and a user-friendly graphical interface running in a Python environment. At the current stage, it features modules to perform 2D PIV and optical camera calibration for multi-camera systems. The PIV module implements an iterative multi-grid image deformation method, in which several parameters can be arbitrarily chosen in order to appropriately tailor the modulation transfer function to the specific application under exam. The calibration module supports accurate calibration with the camera models mostly used in the PIV community: polynomials, rational functions and the pinhole camera model. Among the other features, it supports the integration of the pinhole camera model with a refractive correction model for cylindrical geometries (based on ray-tracing and Snell’s law) and camera calibration procedures working with unknown positions and orientations of the calibration target.