How to read an IGC file

aerofiles has the aerofiles.igc.Reader class for reading IGC files:

with open('track.igc', 'r') as f:
    igc = Reader().read(f)

The result is returned in igc which is a dict containing the IGC file content. The most important keys are header and fix_records. The other keys are mainly self explanatory. Every value consists of two elements. The first is an array of error messages for this key and the second one is a list of the elements. For example igc["fix_records"][0] is a list of possible errors (normally empty) and igc["fix_records"][1] is a list of the fixes. See below for more details.

The constructor of aerofiles.igc.Reader takes an optional argument skip_duplicates which defaults to False. If you set it to true, then all GPS fixes which contain the same time as a previous one will be skipped and not returned as a result.

Headers

The header consists of all header elements of the IGC file. Here is an example of igc["header"][1]:

{'competition_class': '15m Motor Glider',
 'competition_id': 'XYZ-78910',
 'copilot': 'Smith-Barry John A',
 'firmware_revision': '6.4',
 'fix_accuracy': 35,
 'glider_model': 'Schleicher ASH-25',
 'glider_registration': 'ABCD-1234',
 'gps_channels': 12,
 'gps_datum': 'WGS-1984',
 'gps_manufacturer': 'MarconiCanada',
 'gps_max_alt': {'unit': 'm', 'value': 10000},
 'gps_model': 'Superstar',
 'hardware_revision': '3.0',
 'logger_manufacturer': 'Manufacturer',
 'logger_model': 'Model',
 'pilot': 'Bloggs Bill D',
 'pressure_sensor_manufacturer': 'Sensyn',
 'pressure_sensor_max_alt': {'unit': 'm', 'value': 11000},
 'pressure_sensor_model': 'XYZ1111',
 'time_zone_offset': 3.0,
 'utc_date': datetime.date(2001, 7, 16)}],
}

GPS Fixes

The following example IGC file is read. For simplicity it is very short and misses some mandatory fields:

HFDTE160701
HFTZNTIMEZONE:-6.00
B1602405407121N00249342WA002800042120509950

The GPS fixes are found in igc["fix_records"][1] and are a list of dicts for every fix:

[{'ENL': 950,
  'FXA': 205,
  'SIU': 9,
  'datetime': datetime.datetime(2001, 7, 16, 16, 2, 40, tzinfo=<aerofiles.util.timezone.TimeZoneFix object at 0x7fd061c02390>),
  'datetime_local': datetime.datetime(2001, 7, 16, 10, 2, 40, tzinfo=<aerofiles.util.timezone.TimeZoneFix object at 0x7fd061c02120>),
  'gps_alt': 421,
  'lat': 54.11868333333334,
  'lon': -2.8223666666666665,
  'pressure_alt': 280,
  'time': datetime.time(16, 2, 40),
  'validity': 'A'}]

Most values should be self explanatory.

An important aspect are dates, times and timezones. IGC files store all times in UTC. This means that "time" is the time of the fix as found in the IGC and it is always in UTC [1]. The times of the fixes are always increasing as the recording takes part. Normally a flight is recorded during daylight and so you may assume, that there is no roll over taking part. However, as IGC files are recorded in UTC this might not be true. If you record a flight in timezone “-06:00” and you start your flight at “17:59”, then UTC time is already “23:59”. The B record one minute later will be at “00:00”, so it is less than the previous time. You have to handle this yourself, if you use "time".

A solution for this problem is "datetime", which is available since aerofiles v1.4.0. It is a timezone aware instance of datetime.datetime with a timezone of UTC. The date part is taking from the header field HFDTE and the time is taken from the B record. It will be always incrementing, as it also contains a date (which may increase as well in the above example).

If your IGC file contains a HFTZN header telling the timezone where the recording took place, then you will also find "datetime_local". It is the datetime of the fix converted to local time with the given timezone from the header. This is probably the datetime, you are looking for. Please note, that the IGC file specification does not handle a change of timezone during flight. So if you cross borders to a different timezone or daylight savings change occur during flight, then there is no way to record this change in an IGC file. The times of the fixes will then be wrong.

[1]

The time object is an instance of datetime.time and it is “naive”. This means, it has no timezone awareness. It would have been better to make it aware with datetime.UTC, but this has not been done on the first releases of aerofiles. To keep compatibility, we kept it naive. So you find here the exact UTC time as found in the IGC file without any timezone attached.