Impact of the spider position on the CoG measurement. Top: sensitivity to a phase discontinuity and a phase slope with respect to the position of the spider in the subaperture (SA). The spider thickness is 25% of the SA width and the field of view is 3.5 λ/d. The simulation is carried out for a = 0.05 (weak phase regime). Bottom: 1D illustration of the free parameter, the position of the spider, in both the phase discontinuity (left) and the phase slope (right) cases.