How can I Interweave Heart Rate / Power data with GPS files?
How can I trim or crop GPS files for Strava?
How fix bad heart rate data?
How can I convert a FIT file to TCX, GPX, KML or CSV?
How can I repair corrupted GPS files?
Why export as a FIT file?
How to Merge Multiple Strava Tracks
The most common use for this tool is to concatenate two tracks end-to-end after your GPS dies. What happens is you are riding along, and your GPS dies. You then start your phone GPS and start recording your Strava activity once again. Rather than upload two short tracks, you can get credit for the full century (or longer!) ride that you did. Simply go to the main Combine GPS Files for Strava page and upload your files. The tool can accept any compination of GPX, TCX, or FIT files. You can also ZIP any of these three file types for faster uploading. Once you do, you should see a page similar to the one below:
In the image above, the horizonal red and orange bars represent the duration / time of your loaded GPS files. Notice how these tracks do not overlap. In this case, you will want to select all of the "Streams" (notice the checkboxes next to Position, Elevation, and Heart Rate in the table below? Once you send the combined file to Strava, your ride will be full-length! (back to top)
How to interlace Heart Rate and/or power data with position data
Another common use for the tool is to merge Heart Rate data from one device with the Position Data from a GPS. Let's say you already have a heart rate monitor, and you record your GPS track on your phone. You would like to have your heart rate data on Strava along with your map. You can interlace Heart Rate, cadence, power, and/or temperature data from one device with the GPS tracks from another device. Just upload the two (or more) files to the tool on the main Combine GPS Files for Strava page. You should get an page that looks something like the image below (note how the red/orange lines are overlapping in this image as opposed to being end-to-end in the previous image):
In this example, notice how I checked "Heart Rate, Cadence, and Distance" from the first file... and "Position, and Elevation" from the second file. The tool will interweave the heart rate, cadence, and distance with the position and elevation data. Note that I didn't select position data from both files. That is because position can be slightly different between the two GPS units - and if you select both positions in overlapping files, you can potentially accumulate a lot of extra distance due to the small variations in GPS points between the two devices. (back to top)
How to trim or crop files for Strava
Strava now has their own trim/crop feature - but you can trim your files prior to uploading them. Also, sometimes when you are merging files for Strava, you want to only merge part of a file. This is where the trim / crop comes into play. Right now, you can only trim by timestamp. To do this, Check the box in the "Start / End Time" column that says "Check to Edit". After you check that box, you will be able to edit the time stamp boxes that are grayed out by default.
In the image above, you can see that I checked the "Check to Edit" box. You can also see that the start of the first file (red) begins before the second file (orangs). So, I copied the start time from the orange file to the start time of the red file. This means that both files will be trimmed to start at the same time. You can do the same thing for the end time of each file. You can also crop out parts of the GPS file that you don't want to include - such as a bus ride in the middle of your activity. (back to top)
How to fix bad heart rate data on Strava
Sometimes your heart rate monitor can record bad values. This can happen at the beginning of a ride (because the interface between your chest and the heart rate strap is dry and not moistened with sweat). It also happens more often on downhills because the wind can cause your jersey to flap quickly creating static electricity that interferes with the strap. Another cause can be wearing a jacket or vest over a jersey that causes static electricity. It happens more often on dry days than on humid days. Occasionally, some types of heart rate straps can also be influenced by nearby high voltage power lines. Knowing this may help you prevent bad data in the future. Using this tool, you can set a maximum value - and anything above that value will be discarded. In its place, the last known "good" value will be substituted. For example, if your max heart rate is 180, enter that value and if you are flying downhill and your monitor records a heart rate of 255, then the tool will eliminate all of those bad values. Your browser will remember your previous settings so you do not need to enter this every time. (back to top)
How to convert a FIT file to TCX, GPX, KML or CSV
Though you can upload multiple files to the tool, you can also modify a single file for the purpose of conversion or manipulation. Simply upload the file and choose "TCX" or "GPX" as the export type. You can also set the GPS type, the activity type (running, biking, etc). Strava usually shows the selected GPS type, but it is a constant job for them to update their database. Also, it seems that they maintain a separated database for FIT files as well as GPX files. If your GPS type doesn't show correctly on Strava, let us know... but also please create a support ticket with Strava so they can add your new GPS to their database. Chances are that other people will be wanting this too, so the sooner they get notified, the better. (back to top)
How to repair corrupted GPS files
Over the years, people have uploaded thousands of corrupted files to my tool. My tool flags any errors that it detects and saves the files for my later inspection. There are many ways in which a file can be corrupted, so I typically investigate the problem and then write work-around code into the tool so that as much information as possible can be extracted from the corrupted file. For example, if you upload a FIT file with time stamps that are in the future, my tool will look elsewhere within the file for a valid time stamp. If it finds one, the tool will shift all of the other time stamps by that amount. Alternatively, you may upload a truncated TCX or GPX file. Other tools will crash saying that you have improperly formatted XML, but my tool will intelligently extract all of the data that IS present and put it together into a new file. My tool can also read past corrupted FIT file headers, and is capable of retrieving all the different formats for storing Heart Rate, Power, Cadence, and Temperature. If you believe you have one of those streams in a file, but my tool can't extract it, please contact me. Of course, it is not possible to fix an empty file or a severely malformed file, but I have been able to help some people by manually extracting the data for them. If you need this kind of help, please contact me. (back to top)
Benefits of FIT files
For "Power Users", being able to export merged data in the FIT format is a big plus. FIT files can contain information such as total calories, total ascent, Training Stress Score, Training Effect, Normalized Power, Intensity Factor, Strokes, etc... The list of data that you can put into a FIT file is huge. For the most part, Strava ignores many of these fields (Strava tends to recalculate some of this information based on the data in your files and the information you provide in your profile). However, if you are using tools like Garmin Connect or Training Peaks, you are probably going to want to have this additional information embedded. FIT Files are very small in size, but they actually contain significantly more data. In fact, a FIT file with 1 second recording turned on can contain millions of records. I've discovered that some people are trying to merge several days worth of activities that contain millions of data points each. My server can't reliably handle that amount of processing on a large scale, so I have initiated a donation based system to limit the number of "Power Users" who put heavy pressure on the system. That way, we can have a free working tool for everyone. Fewer than 1% of the users participate in the donation program, so this helps keep bandwidth at a reasonable level. (back to top)
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