"Three-dimensional position and velocity information can be extracted by directly analysing the diffraction patterns of seeding particles in imaging velocimetry using realtime CCD cameras. The Generalised Lorenz-Mie theory is shown to yield quantitative accurate models of particle position, such that it can be deduced from typical experimental particle images with an accuracy of the order of 20 µm and an error of 11 grey levels RMS, data obtained by comparing theoretical and experimental images. Both, the theory and experimental verification of the problem presented here are discussed. This thesis present also a method which determines the optimum grid size for interpolated velocimetry data, without making any priori assumptions about the velocity fields, the system used or analysis method. The method employs condition number as the main criterion for deciding the adequate grid size for a given data set. Data sets displayed accordingly are directly comparable, independently of differing experimental parameters or data processing methods. The discussion is based on Computational Fluid Dynamics (CFD) data of flow past the near wake of a cylinder from which simulated PIV images were generated. These images were analysed with the proposed method and the velocity estimates compared to the CFD data. The method was also applied to a sample PIV image of turbulent flow in a baffled tube."