def apply_fit(xy,coeffs):
    """ Apply the coefficients from a linear fit to
        an array of x,y positions.

        The coeffs come from the 'coeffs' member of the
        'fit_arrays()' output.
    """
    x_new = coeffs[0][2] + coeffs[0][0]*xy[:,0] + coeffs[0][1]*xy[:,1]
    y_new = coeffs[1][2] + coeffs[1][0]*xy[:,0] + coeffs[1][1]*xy[:,1]

    return x_new,y_new