2D polyfit of residual from non-linear fitting
Applied a linear 2D polynomial fit to the residual of the fit to the convolution of the rectange and Gaussian. This reduces the RMS residuals from 5% to 0.4%.
Applied a linear 2D polynomial fit to the residual of the fit to the convolution of the rectange and Gaussian. This reduces the RMS residuals from 5% to 0.4%.