Four detailed examples of our POF tool. Top left panel: Observation vignette (data of 2003). Bottom left panel: Model vignette (data of 2009) smoothed by 0″.4, corrected by the exposure map of the observation image (see Eq. 2) and without any shift. Central panel: Statistical landscape obtained when we shift the model vignette of (∆x, ∆y). The values have been subtracted from the minimum value of the landscape. The output vector, velocity, and expansion index are indicated. Right panel: Slices of this landscape (blue triangles along the x-axis and black dots along the y-axis) and the slices of the interpolating 2D polynomial. The horizontal lines correspond to the minimum of the landscape and the ∆cstat value to have 1 sigma uncertainties.