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mileage differences (Read 108 times)

BriChabot


    Sorry if this is a common question, but I did a search and it didn't show up.

     

    I use a TomTom watch and the data uploads directly to their website.  But its nice in that it stores a copy of the data on my PC that is easily importable into RunningAhead (thank you for that option!!!).  My issue is more out of curiousity rather than thinking there's an underlying problem.

     

    Today I did a long run and the watch said 19.72mi.  TomTom said 19.72mi.  But when I import that same data (as a 'fit' file) into RunningAhead it says its 19.4mi.

     

    I had this same thing happen with an older Nike+ watch too where I exported the data an imported it into another program, so its

    not a RunningAhead issue. Its just something I guess in the export process?

     

    Is there something different in the algorithm that sites use to measure the distance between GPS points?

    Thanks for any insights.  Clearly I'm not going to get hung up over a 0.3mi difference.  That's silly.   It just seems funny that

    the same underlying data can give two different answers.


    Feeling the growl again

      My understanding is that RA uses actual National Geographical Survey data.  This should be must more accurate than GPS.  GPS typically measures long.

      "If you want to be a bad a$s, then do what a bad a$s does.  There's your pep talk for today.  Go Run." -- Slo_Hand

       

        Oh, it's better than that:

        TomTom said 19.72mi.

        RA log says 19.36mi.

        RA map says 19.82mi.

         

        I know RA mapping "re-plots" using official data.

        But the log entry?  Not sure why that's a mismatch ...

        “Everything you need is already inside.” -- Bill Bowerman


        day after day sameness

          I apologize for not taking time to search for previous posts on this topic, but I'll wager the answer lies in the difference between "track" distance (when the device and site software adds up the distance between each recorded track point), and the summary data reported by the device.

           

          Say the device reports 9.5 miles as it's summary....the device has calculated this from the track points...calculation on the device.

          Then the uploading site adds up the track points and gets 9.62 miles.

          Then the data is transferred to RA and reports a summary of 9.62 and RA adds up the track points and gets 9.55 miles.

           

          So you end up with a crap load of different numbers.  The summary on the device is the least accurate (my opinion).

          Choosing my words carefully has never been my strength I've been known to be vague and often pointless

          BriChabot


            Wow, all great info and is making me think about it in ways I hadn't considered.  Thanks!

            its pretty interesting to think that GPS watches help in so many ways but also complicate things.

            i appreciate your thoughts on this.