A methodology of the detection of a grid's node positions with sub-pixel accuracy is described. The algorithm uses a correlation method for locating the nodes, determines the neighbourhood relations, then calculates the node positions with sub-pixel accuracy either by locating the local maxima of the correlation function either by centroiding or fining. The accuracy of the algorithm is studied as a function of grid geometry, grid distortion, grid defocus and image noise using synthetic images, and Optimum parameters arc determined. (C) 2008 Elscvier B.V. All rights reserved.