pwx import and timex run trainer (Read 46 times)

    This isn't necessarily a support question but more of a behavior question.  When I import my data into RA from a pwx file.  The total mileage on the summary and the mileage on the map are not the same.  On my latest run for instance the map says it was a total of 6.72 miles and the summary page says it 6.59 which is what the watch says after the run.  So my question is really which on is the more accurate of the 2 as .2 miles is a big difference.  I assume that the map actually uses the coordinates to create the route and I would think it would be the same as the watch regardless of accuracy of the the gps coordinates. I know the gps watches can't be absolutely accurate but I am just wondering why the difference in the two reading from the same data.

      Would you take the answer of both are correct even though they are calculated using the same set of data points?  The workout's distance comes from the summary data in the pwx file.  RA does not verify that value is correct.  In fact, you can change it to anything you want and it will be used.  This is so that if you made adjustments to the numbers before you import, the changes are imported.


      When you display the map, the distance is recalculated based on the data points.  There are multiple equations to calculate distance on earth, believe it or not.  None of them are precise.  The earth is not a perfect sphere.  All distance equations assume certain initial values to describe the earth's radii.


      Most GPSes use the great circle distance algorithm to calculate distance between two latitude/longitude pairs.  It is a computationally quick formula that provide good enough results.  RA uses a different formula that's supposed to be more accurate but more complex.  The difference when compared to the great circle distance algorithm can be up to 5%.  The 0.2 miles is about 3% so it is within this range.

        Perfect answer.  I was more interested in how the numbers were figured and that makes sense to me.  So that behavior would exist regardless of the gps brand and is probably different with each one while the map distance would be the same across watch brands assuming they have the same gps readings points.