Seven dither patterns that we have analysed shown in the spacecraft reference frame (see Fig. 2). For clarity, a shift of 5″ (or of −5″) in the Xsc direction is applied to the ‘J’ (or to the ‘N’) pattern in the figure so as to distinguish it from the ‘S’ pattern. Only the ‘J’ and the ‘S’ patterns, the first two steps of which are identical, are fully compliant with the stringent survey requirements.