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
