Thursday, January 01, 2015

Merging Garmin Heart Rate data with Activities

I was lucky enough to receive a Garmin Vivofit recently and am really happy with it so far.

It does a good job for what it's meant to do. My primary use is for Heart Rate monitoring when exercising, but I'm also interested in the step counts and goals.

I haven't used the Garmin Connect website in a while - and it's latest incarnation has quite a pleasing design.

One thing I quickly realised though is that there is still no way to combine the data from my  Garmin Edge 200, and my HR data - either from my Vivofit or Garmin FR60.

You can synchronise each activity fine, but not combine them - well, at least I couldn't see an easy way to do this. Please correct me if I'm wrong.

A little googling showed that this is quite a common problem, and naturally enough there were a number of solutions as well.

Essentially it provided a simple XSL transform to merge the two files. There was also a subsequent little java app which embedded the transform and provided a simple little GUI.

The results for me did not work however. Not sure if it was just me, or that the schema had since changed.

I was keen to get the HR data on the same display though, so spent an afternoon tinkering.

The process I used to get started was:
  1. Synchronise the clocks from the Garmin Edge 200, and that of the FR60. You need to use the Edge 200 as the source - since it is based on the GPS clock, and hence you can't change this one.
  2. Went for a ride, starting the activities at more or less the same time
  3. Synchronise each device with the Garmin Connect
  4. Retrieve each activity as a TCX file
I now had some data to work with.

The raw Cycle file looked like this:

You can easily see the straight forward capture of each tracking point.

The HR data is very similar:
Again, very straight forward. 

I took a very standard approach to tinkering ... manipulate the file - manually at first - until you get a format that's acceptable to the Garmin Connect uploader.

At first, I tried the simplest thing - of copying in all track points containing HR data - after the cycle ones. Which didn't work.

Next try was to adjust every Cycle tracepoint to include a HR data point - which was just a constant. To validate this, a simple all change via Sublime Text did the trick. I also manually added the HR summary data to the Lap header information - and ... success.

So now I knew what the format should be - and it was just a simple matter of programming to write an app to do that.

I dusted off some old familiar tools:
  • Eclipse
  • Java
  • JDOM for xml handling
The main thing I wanted do was to drive the process from the Cycle data - after all, we simply wanted to annotate each cycle track point with the most appropriate HR data point.

The high level view is to:
  • read the Cycle data
  • read the HR data
  • for each cycle track point
    • find the appropriate HR track point
      • if the HR data hadn't started yet - simply use the first one
      • or, if there is an exact match, use it
      • or, use the latest HR track point which is earlier than the cycle track point
      • or, if the HR data has ended prematurely - just use the last HR track point
    • add the HR element to the cycle element
  • extract the HR summary data and add it to the Lap header
Simple really.

The result is something like this:

The last remaining steps were to:
  • remove the Cycle activity from Garmin Connect
  • upload the newly combined activity - which has the same internal activity ID
And then - Garmin Connect displays the data as I wanted to:

As an added bonus, you can click on the dual arrows to the right of each chart - to then select a larger zoomed display - and overlay the other data:

I hope to tidy up the code soon, and post it to see if others would like to use it.


tsanga13 said...

Hi Evan,

Do you mind sharing what you did? I'm in exactly the same situation needing to merge heart rate data with GPS data captured with my phone, both in tcx.


Unknown said...

Hey any updates on the code. I'm planning to do the same with some changes in mind. It would help me a lot if I could see your code firstly. Thanks