PyPIV is a Python reproduction of a Matlab toolbox for Particle Image Velocimetry (PIV) analysis.

PIV gives displacement in pixels, to know the displacement in your units you multiply it by the scaling of cm/pixel, i.e. by 50 cm/pixel. To know the speed, the displacement is divided by the time separation, i.e. by 0.5 seconds, then we get: sclt = 50 cm/pixels / 0.5 = 100 [cm/seconds/pixels]. For example, if the vector is 10 pixels, then the result will be 100 * 10 = 1000 cm/s