Track distance in BaseCamp vs XT

[tombarrington]

While fiddling with the XT, BaseCamp, and MRA Routeplanner I came across a couple of situations I could not explain. This one has to do with the length of the track as calculated in BaseCamp compared to the same track displayed on the XT.

The first image shows the track's information pane from BaseCamp. It shows the track to be 477 miles. The second image shows the XT Saved Tracks screen indicating the track is 502 miles. Thoughts on this discrepancy? As far as I know, the track is not "recalculated" when saved to the XT and for what it's worth the source route length matches in both BaseCamp and the XT at 477 miles. When I toggle between the route and the track in BaseCamp they correspond exactly.





You'll see there is a track starting with "MRA" also loaded. This relates to the other situation which will be a separate post.

Thanks in advance for your thoughts.

[sussamb]

Known bug in BaseCamp occasionally calculates distance incorrectly. Normally can be forced to do the correct calculation by deleting a point in the track.

[tombarrington]

Can't dispute that but in this case the track and route in BaseCamp agreed at 477 miles. Once loaded into the XT the route was still 477 miles but the track became 502 miles. Scratching my head.

[Peobody]

I am very curious about this because when I look at my list of saved tracks, the distance listed is the distance to the starting point. A specific one I am looking at now show 19 miles in the Saved Tracks list for a route that is 188 miles long. The 19 miles is about right for the distance to its starting point. This discussion is talking about the length of the track, not the distance to its starting point, right?

[tombarrington]

@Peobody, I’m describing something different. This is a track created in BaseCamp to complement my route. The track and route length match in BaseCamp but not on the XT.

[Peobody]

Still curious... How do you see the length of a track on the XT?

[tombarrington]

See the second image in the first post. It’s where one would go to show the track on the map. Like many XT users I always import the tracks from BaseCamp and make them visible in case I deviate from the route.

[sussamb]

Can't dispute that but in this case the track and route in BaseCamp agreed at 477 miles. Once loaded into the XT the route was still 477 miles but the track became 502 miles. Scratching my head.

Yes, and I suspect if you allow BaseCamp to recalculate the track it will then agree with the distance showing on your device. The fact that track length and route length in BaseCamp agree at 477 is immaterial as I'd expect them to be different as there are many more route points in a track so the distance should be greater.

[jfheath]

Can't dispute that but in this case the track and route in BaseCamp agreed at 477 miles. Once loaded into the XT the route was still 477 miles but the track became 502 miles. Scratching my head.

Yes, and I suspect if you allow BaseCamp to recalculate the track it will then agree with the distance showing on your device. The fact that track length and route length in BaseCamp agree at 477 is immaterial as I'd expect them to be different as there are many more route points in a track so the distance should be greater.

This is most odd.

If the track has been created by Basecamp from the route - all it has to do is to take every route point - and I mean every route point <rtept>, including the invisible ghost point gpxx route point extensions - and change each tag to track point <trkpt>

As soon as the Zumo gets the track - it will be identical to what was in Basecamp.
As soon as the Zumo gets the route - it may recalculate it, find a shorter or a longer route than the original. It may include the distance from current position to reach the startpoint.

But why the track on the Zumo should be longer than the same track on Basecamp - that is very odd. As far as I know, the track doesn't alter. It is a collection of many hundreds of points connected together with short straight lines. All it has to do is apply pythagoras to calculate the hypotenuse between pairs of adjacent points and add them together. Curvature of the earth is of little consequence for such short distances. It sounds like a lot of processing, but really that is trivial even for a computer running at 'just' tens of millions of clock ticks per second..

Turning a track to a trip - well that's not the same thing at all. But I don't believe that you have done that.

Although I note that Basecamp uses many more significant figures in the lat/long coordinates than does the later Zumos.

Stumped.

[Peobody]

I'm transitioning from curious to confused. This is my "Saved tracks" list when accessed via Apps > Tracks. All distance are to the Start point at the exit of my neighborhood. I don't find a setting that could change this. Did I miss it?

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