GPS, Running Watches, Phones, Accuracy and other stuff pt 3

Enter FME

FME is a massively powerful GIS data manipulation tool.  For professional use it isn't cheap, but those very nice people at Safe Software (who make FME) allow free Home use - if you ask them nicely and say what you plan to do with it.  

I have a little experience with FME from work, and work with someone with a shed load more (many thanks Matt) so with my ideas and his pointers as to what tools to use, I have made this first attempt at quantifying accuracy.

Let's look at a recent run


The yellow line is a best fit line using open source mapping and google aerial images.

The red is what my Gear Fit tracked.

Now, my working theory is that by making polygons between these two (the grey areas) I should get a measure of how good the tracker was.  The smaller the overall area, the better the track was on that day

The results for this first test are below -


The overall Error Area (as i am calling it) is 56576.6 m2 - a lot of that is at the start of the run where the Gear Fit obviously hadn't locked in properly.


If you click on the grey area you will also get info about the lengths of the two routes, plus the number of records in the GPX file that was exported from the Gear Fit

Same Device - different software

Ok, I tracked my walk to work on my phone using the Android Endomondo app and Locus maps - Locus is a very good mapping package written by a map geek.  The good thing about it, for this task, is yo can change the frequency that the points are recorded at.  I had it today at every 5 seconds

This is a section - remember -same device, so same GPS fix.  The blue line is Locus, the red Endomondo.  You can see that if those two red points above and below the blue line had been recorded by Locus, the distance would have been compromised. So, just seconds different in the recording of the data can have an impact.

The rest of the route was very similar.  BTW, the green line is the "real" route as plotted using the best UK maps available.

More on Page 4

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