fit

A parser for Garmin FIT data files
README

FIT

This is a minimal OCaml project to parse FIT files as they are
produced by personal fitness devices. The main purpose of FIT is to
provide a library for reading such FIT files but in addition it includes
a small command line tool to emit FIT files in JSON format.

FIT is a binary format invented by Garmin that groups basic values in
records, which typically include a timestamp. Below is such a record in
JSON format as emitted by the tool.

{
  "msg": "20",
  "13": 11,
  "2": 1900,
  "5": 1732414,
  "6": 0,
  "1": 1669620,
  "0": 622905943,
  "253": 971857351
}

Each record has a global message number (like 20) which defines the purpose
of the record and a number of values in position slots. The meaning of
these is defined in the FIT Protocol but this library (so far) only
implements the parsing. For example, message 20 is called record in
the FIT protocol and slots have these meanings:

  • 0 position_lat

  • 1 position_long

  • 2 altitude

  • 5 distance

  • 6 speed

  • 13 temperature

  • 253 timestamp

Values are further scaled and shifted, which is also defined in the
protocol, and this transformation is only implemented for a few fields
of the "record" message:

{
  "msg": "69",
  "0": 4
},
{
  "msg": "record",
  "timestamp": "2020-10-17T06:24:03",
  "latitude": 52.21163995563984,
  "longitude": 0.1410909835249186,
  "speed": 2.767,
  "distance": 65.54000000000001,
  "altitude": -118.8,
  "temperature": 10
},

As can be seen above, FIT does not implement decoding of "69" message
blocks. The "record" (20) block is usually the one we are interested in
and FIT implements decoding of the most interesing fields.

CLI

This code is primarily intended as a library but it also provides a
small binary. The fit command emits the data to stdout in JSON format.
I am using this currently for inspecting FIT files. The FIT file in
data/ is from a bike computer.

$ fit data/xpress-4x-2020-10-17.fit | head -25
[
  {
    "msg": "0",
    "3": 5122,
    "4": 971850094,
    "1": 267,
    "2": 1803,
    "5": 0,
    "0": 4
  },
  {
    "msg": "68",
    "0": 17,
    "1": 1,
    "2": 0,
    "3": 10,
    "4": 255,
    "5": 0,
    "6": 0,
    "7": 0,
    "8": 232,
    "9": 0,
    "10": 60,
    "11": 19693
  },
  ...

Installing FIT

Version 1.0.1 has been published as an Opam package such that it can
be installed from Opam:

opam install fit

You can also pin it directly for access to unpublished changes:

opam pin add -y git+https://github.com/lindig/fit

Once installed, you can use it:

$ utop -require fit -require rresult
utop # open Rresult;;
utop # Fit.read "data/xpress-4x-2020-10-17.fit" >>= fun fit ->
       Fit.to_json |> R.return;;

The fit binary takes a FIT file as argument:

$ fit data/xpress-4x-2020-10-17.fit | tail -15
    "58": 11,
    "20": null,
    "21": null
  },
  {
    "msg": "activity",
    "timestamp": "2020-10-17T08:22:35",
    "0": 7263000,
    "5": 971860957,
    "1": 1,
    "2": 0,
    "3": 26,
    "4": 1
  }
$ fit --help

Resources

  • https://developer.garmin.com/fit/protocol/

  • https://www.pinns.co.uk/osm/fit-for-dummies.html

Contribute

If you find this useful, please contribute back by raising pull
requests for improvements you made.

Install
Published
02 Aug 2022
Sources
fit-1.0.3.tbz
sha256=559ecb941426300106114c76b0cbbd62a9c95719b4cf2f81f00693d8b0281164
sha512=69c95be4e92e87752e0f13fb2c1a964df0ef52dde64ff6ce46ac5bf46f1c0d6df59cb87217a71424e227618ac9e09b3b2be0a3deb4bed4b04926267577c863ca
Dependencies
ISO8601
>= "0.2.6"
rresult
>= "0.6.0"
ezjsonm
>= "1.2.0"
angstrom
>= "0.15.0"
cmdliner
>= "1.1.0"
dune
>= "2.0"
ocaml
>= "4.08.0"
Reverse Dependencies