A method of generating a polyline representing a contour of one or more objects includes the steps a) formulating a series of spatially ordered points in 2-dimensional space, each representing a (point) detection with respect to object(s); b) connecting the end points of the series of ordered points with a first straight line segment, and determining the shortest distance between each of the intermediate points and the first segment; c) determining from step b) a threshold based on a measure of the dispersion of the intermediate points around the segment; d) for each side of the segment determining, for any points that lie on that respective side, the point which is further from the segment; e) determining any of the points found in step d) which are further from the segment than the threshold; f) formulating a polyline by connecting the end points of the points determined from step e).