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Forerunner 245 distance short

Pieri70
over 2 years ago

Hello everybody

I own a forerunner 245 for more than a year now. I use it in open air, run, MTB and trekking. No city recordings.

As I compare tracks measurements with friends my one is always shorter, often really different.

Today I tried to measure a walking session (4000m with 200m descent/ascent) recorded with my 245.

I exported the GPX from connect and imported it into a GIS (QGIS professional cartographic software).

I worked on single measurement points, I get elevation measurements from a high resolution DTM (Digital terrain model), a model officially distributed by our country, 1m X,Y resolution.

Then I reconstructed the path to get a corrected Z interpolated polyline and I compared elevations and distance between what Connect gives me and what is obtained with my conversion.

Elevations are "almost good".

Bigger differences are at sea level, I went from home to the sea down the coast and along it, then I climbed back home.

245VSDTM

Then I calculated the 2D and 3D distance of the path

245VSDTMDistance

Connect gives me 3.92Km that is less than "lunghezza" (2D distance) 4001 meters, that is less than real 3D distance (4139 meters).

It's almost 220 meters difference on 4140 meters path (5.3%)

Is this normal?

Thanks

Pietro

  • 0 over 2 years ago

    Try changing data recording in system to every second instead of smart. That improved gps precision greatly for me.

  • 0 over 2 years ago in reply to PallMe

    I'll try

    but the simulation I made is based on the same GPS readings (points) taken by current GPS setup.

    I mean, If my GPS record a point every 10 seconds, the path I calculated passes trought the same points taken every 10 seconds so distances should be the same..
    That isn't so.

    Anyway, I'll try your suggestion

  • 0 over 2 years ago in reply to Pieri70

    It easier to judge the precision on a satelite map. With smart, it was cutting corners all over the place. This was in a city environment with lots of 90degree turns.