package fit
Install
Dune Dependency
Authors
Maintainers
Sources
sha256=559ecb941426300106114c76b0cbbd62a9c95719b4cf2f81f00693d8b0281164
sha512=69c95be4e92e87752e0f13fb2c1a964df0ef52dde64ff6ce46ac5bf46f1c0d6df59cb87217a71424e227618ac9e09b3b2be0a3deb4bed4b04926267577c863ca
Description
Fit is library for reading FIT files as they are produced by Garmin and other fitness devices. It comes with a small command-line tool to emit some of that information as JSON, mostly for debugging. Fit is not comprehensive but reads the most important records from a FIT file that contains the actual periodic measurements.
Published: 02 Aug 2022
README
README.md
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.