def task_to_string(df_task, sep=',', sep_points=" "):
    """
    Returns a string from a task DataFrame
    with sep=',' and sep_points=" "
    like:
    '5.9840002060,44.0549011230,1500.0 6.0107221603,44.0150871277,1500.0 6.3285999298,44.0536003113,1600.0 6.5361166000,44.2888832092,2700.0 6.3811173439,44.4144477844,2200.0 5.9840002060,44.0549011230,1500.0'
    'lon1,lat1,alt1 lon2,lat2,alt2'
    """
    return(sep_points.join(
        df_task.apply(lambda tp: "%.10f%s%.10f%s%.1f" %
         (tp.Lon, sep, tp.Lat, sep, tp.Altitude), axis=1)))