def open_edge_points(R, R_true, s=6):
    """
    Opens measured curves at the edges of FOV

    Args:
        R (ndarray):
            empty/sparse data
        R_true (ndarray):
            "ground truth"
        s (int):
            step value, which determines the density of opened edge points

    Returns:
        3D ndarray with opened edge points
    """
    e1, e2 = R_true.shape[:2]
    R[0, ::s] = R_true[0, ::s]
    R[::s, 0] = R_true[::s, 0]
    R[e1-1, s:e2-s:s] = R_true[e1-1, s:e2-s:s]
    R[s::s, e2-1] = R_true[s::s, e2-1]
    return R