Raymarine forum

Question -

On my most recent track, I show 88 sm on the track screen. When I export the gpx file to a third party application or gpx mapping site, they show around 90.1 -90.2 sm.

I'm on the most recent software update (v12.10).

Dragonfly 7 Pro : 6798 pts / 88.0 sm
GPS Analyzer: 6798 pts / 90.11 sm
JavaWa GPS: 6798 pts / 90.18 sm

I can see some difference based on how many decimals someone uses in their calculations, but ~2% seems a bit high.

Any thoughts on the difference?

-E

Welcome to the Raymarine Forum Ed,

My suspicion is that round off error, combined with the utilized precision, is responsible for the difference in calculated track lengths. With each leg of a track, the MFD sums the distance between each successive track leg. Unlike routes which have relatively few (199) legs, tracks can have up to 9,999 legs. Such precision/rounding differences encountered within mathematical calculations will typically increase with the number of calculations. Accordingly, it is less likely the length of the track, but rather the number of track points within the track which will cause the calculations to differ. In its default mode, the frequency that track points are created within Dragonfly displays and MFDs will increase as the amount of frequency of course changes increase. Similarly, in its default mode, the frequency that track points are created within Dragonfly displays and MFDs will be reduced when the vessel is traveling in a straight line.

We'll be glad to look into this should you attach a GPX file containing the subject track to a response to this thread.