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A MAVLink telemetry (.tlog) file parser - similarish to mavlogdump, but (I think) nicer to use and process afterwards
#!/usr/bin/env python3
''' Mavlink telemetry (.tlog) file parser.
Operates as a generator. Allows csv output or listing useful types/fields.
import json
from pathlib import Path
from fnmatch import fnmatch
from pymavlink import mavutil
from inspect import getfullargspec
class Telemetry:
'VFR_HUD' : ['heading', 'alt', 'climb'],
'VIBRATION' : [f'vibration_{axis}' for axis in 'xyz'],
'SCALED_IMU2' : [s for axis in 'xyz'
for s in (axis+'acc', axis+'gyro')],
'ATTITUDE' : [s for rot in ('roll', 'pitch', 'yaw')
for s in (rot, rot+'speed')],
'SCALED_PRESSURE2' : ['temperature'],
def __init__(self, log_file, fields=DEFAULT_FIELDS,
''' Creates a tlog parser on 'log_file', extracting 'fields'.
'log_file' can be a string filename/path, or pathlib.Path instance.
'fields' is either a dictionary in the form {'TYPE': ['attr']/None},
or a string filename/path to a json/text file with the same
structure. Specifying None (null if in a file) instead of an
attribute list gets all the attributes for that type.
Defaults to Telemetry.DEFAULT_FIELDS.
'dialect' is a string specifying the mavlink parsing dialect to use.
Default 'ardupilotmega'.
self.log_file = str(log_file) # mavutil doesn't use Path
self.mlog = mavutil.mavlink_connection(self.log_file, dialect=dialect)
def _init_fields(self, fields):
''' Determine CSV fields and populate None attribute lists. '''
if isinstance(fields, (str, Path)):
with open(fields) as field_file:
fields = json.load(field_file)
self.csv_fields = ['timestamp']
nan = float('nan') # start with non-number data values = [nan]
self.offsets = {}
for type_, field in fields.items():
if field is None:
type_class = f'MAVLink_{type_.lower()}_message'
fields[type_] = \
self.offsets[type_] = offset = len(self.csv_fields)
self.csv_fields.extend(f'{type_}.{attr}' for attr in fields[type_]) for _ in range(len(self.csv_fields) - offset))
self.fields = fields
self.type_set = set(fields) # put major fields in a set
def __enter__(self):
return self
def __exit__(self, *exc):
def __iter__(self):
''' Iterate through available messages. '''
# remove the starting hash from the following line to make Python 3.7 compatible
while msg := self.mlog.recv_match(type=self.type_set):
while "messages available":
msg = self.mlog.recv_match(type=self.type_set)
if not msg:
m_type = msg.get_type()
if m_type == 'BAD_DATA':
print('bad data recorded')
elif not self.match_types(m_type, self.type_set):
# keep going if the message is the wrong type
# NOTE: specifically relevant because recv_match internal
# 'skip_to_type' function auto-includes HEARTBEAT and
# PARAM_VALUE messages
yield msg
def match_types(m_type, patterns):
''' Return True if m_type matches one of patterns.
'patterns' are types but case-insensitive on Windows, and with support
for unix-style wildcards:
* -> match everything
? -> match a single character
[seq] -> match any character in seq
[!seq] -> match any character not in seq
return any(fnmatch(m_type, p) for p in patterns)
def to_csv(self, output=None, csv_sep=',', verbose=True):
NOTE: opens output in append mode
-> can create files, but WILL NOT overwrite existing files
(adds to the end instead).
if output is None:
output = Path(self.log_file).with_suffix('.csv')
if verbose:
print(f'Processing {self.log_file}\n -> Saving to {output}')
last_timestamp = None
adding = Path(output).is_file()
# TODO enable stdout output for printing to terminal?
with self as mavlink, open(output, 'a') as out_file:
def write_line(data):
print(csv_sep.join(data), file=out_file)
# convert to suitable for csv output = [str(val) for val in]
if not adding:
write_line(self.csv_fields) # field headings
for msg in mavlink:
wrote_last = False
timestamp = getattr(msg, '_timestamp', 0.0)
data = msg.to_dict()
if last_timestamp is not None and timestamp != last_timestamp:
# new timestamp, so write latest data and timestamp[0] = f'{last_timestamp:.8f}'
wrote_last = True
self._update(msg.get_type(), data, convert=str)
last_timestamp = timestamp
if not wrote_last: # handle last message[0] = f'{last_timestamp:.8f}'
except UnboundLocalError:
print('No desired messages found in file')
def data_parser(self):
last_timestamp = None
with self as mavlink:
for msg in mavlink:
yielded_last = False
timestamp = getattr(msg, '_timestamp', 0.0)
data = msg.to_dict()
if last_timestamp is not None and timestamp != last_timestamp:
# new timestamp, so yield latest data and timestamp[0] = last_timestamp
yielded_last = True
self._update(msg.get_type(), data)
last_timestamp = timestamp
if not yielded_last: # handle last message[0] = last_timestamp
except UnboundLocalError:
print('No desired messages found in file')
def _update(self, type_, data, convert=lambda d: d):
''' Update with the latest data for 'type_'. '''
offset = self.offsets[type_]
for index, desired_attr in enumerate(self.fields[type_]):[offset+index] = convert(data[desired_attr])
def logs_to_csv(cls, output, logs, fields=DEFAULT_FIELDS, csv_sep=',',
dialect='ardupilotmega', verbose=True):
for log in logs:
cls(log, fields, dialect).to_csv(output, csv_sep, verbose)
def csv_to_df(filename, timestamp='timestamp',
timezone='Australia/Melbourne', **kwargs):
''' Returns a pandas dataframe of a csv-log, indexed by timestamp.
'filename' is the path to a csv-file, as output by Telemetry.to_csv
'timestamp' is the name of the timestamp column. Defaults to
'timezone' is the location where the data was collected. Data is
assumed to be in UTC, and is converted to the specified timezone.
Defaults to 'Australia/Melbourne'.
'kwargs' are additional key-word arguments to pass to pandas read_csv.
Mostly useful for 'usecols', if not all columns are required.
import pandas as pd
def parser(utc_epoch_seconds):
return (pd.to_datetime(utc_epoch_seconds, unit='s')
return pd.read_csv(filename, index_col=timestamp,
parse_dates=[timestamp], date_parser=parser,
def get_useful_fields(cls, tlogs, out='useful.json', fields=None,
dialect='ardupilotmega', verbose=True):
''' Returns a {type: [fields]} dictionary of all non-constant fields.
'tlogs' should be an iterable of one or more string/Path filepaths.
'out' is the filename to save to. If set to None does not save.
'fields' a json file for a subset of fields to parse with. If left as
None checks all fields in the file.
'dialect' is the mavlink dialect in use. Default 'ardupilotmega'.
'verbose' a boolean determining if progress updates should be printed.
mavutil.set_dialect(dialect) # set dialect so field tracker is accurate
fields = cls.__create_field_tracker(fields)
# determine fields dictionary to initialise with
init_fields = {type_: list(fields_)
for type_, fields_ in fields.items()}
useful_types = {}
for tlog in tlogs:
if verbose:
print(f'Extracting useful fields from {tlog!r}')
with cls(tlog, init_fields, dialect) as mavlink:
for msg in mavlink:
cls.__process(msg, mavlink, fields, init_fields,
useful_types = {t: useful_types[t] for t in sorted(useful_types)}
if out:
with open(out, 'w') as output:
json.dump(useful_types, output, indent=4)
if verbose:
print(f' -> Saving to {output}')
return useful_types
def __create_field_tracker(fields):
''' Create a dictionary of {type: {field: None}} for specified fields.
If 'fields' is None gets all the types and fields from mavutil.mavlink.
If 'fields' is a string/Path json file, reads in and replaces any
None fields with all the valid fields for that type.
def get_fields(type_):
''' Return a dict of {field: None} for all fields of type_. '''
return {field: None for field in
if fields is None:
fields = {t[8:-8].upper(): get_fields(t)
for t in dir(mavutil.mavlink)
if t.startswith('MAVLink_') and t.endswith('_message')}
elif isinstance(fields, (str, Path)):
fmt = 'MAVLink_{}_message'
with open(fields) as in_file:
fields = {type_: ({field: None for field in fields_} if fields_
else get_fields(fmt.format(type_.lower())))
for type_, fields_ in json.load(in_file).items()}
return fields
def __process(msg, mavlink, fields, init_fields, useful_types):
msg_type = msg.get_type()
to_remove = []
for field, data in fields[msg_type].items():
msg_data = getattr(msg, field)
if data is None:
fields[msg_type][field] = msg_data
elif msg_data != data:
# data changes -> useful field
if msg_type not in useful_types:
useful_types[msg_type] = []
if not fields[msg_type]:
# all fields useful -> stop checking type
for field in to_remove:
if __name__ == '__main__':
from argparse import ArgumentParser
parser = ArgumentParser(description=__doc__)
parser.add_argument('-o', '--output', default=None, type=str,
help=('output filename '
'(defaults to existing tlog name(s) for csv,'
' no default if using --list - specify json'
' filename if desired)'))
parser.add_argument('-f', '--fields', default=None, type=str,
help='fields subset to parse with (json file)')
parser.add_argument('-d', '--dialect', default='ardupilotmega', type=str,
help='mavlink dialect to parse with')
parser.add_argument('-t', '--tlogs', required=True, nargs='*',
help='tlog filename(s)/path(s) to parse')
parser.add_argument('-l', '--list', action='store_true',
help='list useful (non-constant) fields')
parser.add_argument('-q', '--quiet', action='store_true',
help='turn off printed output')
args = parser.parse_args()
verbose = not args.quiet
if args.list:
fields = Telemetry.get_useful_fields(args.tlogs, args.output,
args.fields, args.dialect,
if verbose:
print(json.dumps(fields, indent=4))
fields = args.fields or Telemetry.DEFAULT_FIELDS
Telemetry.logs_to_csv(args.output, args.tlogs, fields, verbose=verbose)
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ES-Alexander commented Oct 30, 2021


The code presented here is intended for programmatic use (e.g. aligning telemetry with other data, such as a video stream or sonar logs), or for detailed analysis where fields are plotted against each other (e.g. to determine correlation).

If you're only interested in directly visualising your .tlog data (viewing trajectory on a satellite map, and/or plotting different fields over time), you should use a dedicated tool like Log Viewer.

Web Demo

An online notebook demo of this code is available, which can be used for converting .tlog files to .csv, and simple plotting/analysis.

Note that it runs in Google's cloud servers, so upload, download, and processing times can be significant. If you're planning to use the functionality regularly for different log files, it's worth copying the code and running it locally instead.

Running Locally (on your computer)

Requires Python >= 3.8, and pymavlink should be installed (e.g. python3 -m pip install pymavlink)
(can modify __iter__ to make Python 3.7-compatible if necessary)

Usage Options

Getting available fields from telemetry file(s)

  • use --tlogs to specify one or more .tlog files to analyse
  • use --list to find fields within them
  • use --output to specify a file to save those fields to in json format (if desired)
  • prints output to terminal by default - use --quiet to avoid printing
python3 --list --output my_fields.json --tlogs "2021-10-30 17:09:56.tlog" "2021-10-30 17:40:13.tlog"

Edit the json file to remove any fields you're not interested in (making sure to keep the result as valid json - don't remove closing braces, and don't leave trailing commas).

Getting a .csv file from telemetry file(s)

  • use --tlogs to specify one or more .tlog files to analyse
  • use --fields to specify a json file of fields (see above for how to get one)
    • can leave off if you just want to use the defaults (heading (compass), alt (depth), and climb; 3D vibration, acceleration, and gyro; roll, pitch, and yaw (including speed for each); temperature (external)
  • use --output to specify one file to save all the csv data to
    • can leave off if the default behaviour of one csv per .tlog is preferred
    • generated csv(s) intended for automatic parsing/processing, so timestamp is left in UTC "seconds since UNIX epoch" format
  • use --quiet to avoid printing status updates (which file is being processed, and where the results are being saved)
python3 --fields my_fields.json --output "2021-10-30_combined.csv" --tlogs "2021-10-30 17:09:56.tlog" "2021-10-30 17:40:13.tlog"

Getting a pandas.DataFrame from a .csv file

  • Requires pandas to be installed (e.g. python3 -m pip install pandas)
  • Uses pytz timezones, which can be either relative to GMT/UTC (e.g. 'Etc/GMT+3' or 'Etc/GMT-4') or based on Location (e.g. 'US/Eastern', 'Asia/Tokyo', etc - defaults to Australia/Melbourne)
  • Timezone handling automatically deals with things like daylight savings and leap years, so is quite useful
from mavlogparse import Telemetry

df = Telemetry.csv_to_df('2021-10-30_combined.csv', timezone='US/Eastern')

Basic Plotting with Matplotlib

  • Requires matplotlib to be installed (e.g. python3 -m pip install matplotlib)
import matplotlib.pyplot as plt
from mavlogparse import Telemetry

df = Telemetry.csv_to_df('2021-10-30_combined.csv')
#df.plot() # literally everything over time (almost always a bad idea)
df['VFR_HUD.alt'].plot() # depth over time
... # configure as desired # display the plot (blocking - close plot to continue, or use `` instead)

# plot the IMU's measured rotation speed about the x-axis, and the rollspeed determined by the Kalman Filter
df['SCALED_IMU2.xgyro'] /= 1000 # convert mrad/s -> rad/s for direct comparison
df[['SCALED_IMU2.xgyro', 'ATTITUDE.rollspeed']].plot()

# plot depth against temperature
plt.scatter(df['VFR_HUD.alt'], df['SCALED_PRESSURE2.temperature'] / 100)
plt.xlabel('depth [m]')
plt.ylabel('temperature [deg C]')

# plot depth over time, coloured by heading (see which direction each dive was facing)
plt.scatter(df.index, df['VFR_HUD.alt'], cmap='hsv', c=df['VFR_HUD.heading'].fillna(0), s=1)
cbar = plt.colorbar(ticks=[0,90,170,270,359])['N','E','S','W','N'])

Basic Plotting with Plotly

  • Requires plotly to be installed (e.g. python3 -m pip install plotly)
  • More interactive than matplotlib
    • Easier to compare variables (separate y-axes can easily be moved relative to each other)
  • Runs in the browser
    • Can right-click/Save As to save the page as html, which means the interactive plot can be saved and sent to others
import as px
from mavlogparse import Telemetry

df = Telemetry.csv_to_df('2021-10-30_combined.csv')
fig = px.scatter(df, x='VFR_HUD.alt', y='SCALED_PRESSURE2.temperature')

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