Wednesday, June 8, 2016

GPS device that generates incorrect data in gpx format files

One of our users recorded a route in two GPS devices: Garmin and Polar

The results displayed by IBPindex were pretty similar. Oddly, the analysis of the files generated by Polar was rather different depending on whether the format of the file was GPX or TCX.

After the analysis of the files we found that, for the same route, the device included different data in the file depending on whether the format was GPX or TCX.

We quote here the question of the user:



Good evening,

I have a question I would like you to solve for me, if possible.

I have a Polar M400 and Garmin Vista HCX. Polar allows me to download data from the same route in formats GPX and TCX, and only GPX in the case of Garmin.

When analyzing the files with IBPindex, I find three different results. I could understand differences between Polar and Garmin, all in all, these are different devices and configuration settings can be also different.

But, in the case of Polar, the same track gives very different results depending on the format you download it (either GPX or TCX).

What can be happening?

I send you attached the three files.

And the conclusions of our analysis:

The correct tracks are "2016_06_05 _-_ garmin_vista_hcx.gpx" and "2016_06_05 _-_ polar_m400.tcx".  

"2016_06_05 _-_ polar_m400.gpx" is incorrect.

This image shows a comparison of the data exported from Polar in the GPX and TCX files.

TCX GPX data comparison

The GPX height data accumulates many mistakes. It seems there may be something wrong in the conversion process to GPX. 

It would be very interesting to see if this only happens with this trails or happens in all cases.

If you can do some tests, please let me know what are the results. Is there perhaps a problem in the firmware of the device?

Joan Casares

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