Centroiding error for WCoG due to RON and photon noise for an LGS with an 8 m telescope and a 16 × 16 subaperture SH with 100 photons per subaperture per frame. The black curve corresponds to the E2E simulations, the red line to the predicted centroiding variance due to RON, the blue line to the predicted variance due to photon noise and the green line the sum of the two. Both X and Y centroiding variances are shown in the same plot, the left part of the plot is for the variance along the X axis and the right part of the plot is the variance along the Y axis