Basecamp -> Zumo mileage change

[meagvg]

Hello. First time posting here.

I'm trying to understand why my Basecamp (Mac) route mileage is altered after sending to the Zumo. The Zumo adds ~50 miles to a 1500 mile route.
I use a start/stop waypoint and 85 shaping points along the route. All interstate. It's a long, but simple route.

Maps are identical in Basecamp and Zumo.
All shaping points have been double checked for accuracy. Profiles are matched.
Recalc on the Zumo takes about 10 seconds.

If I export the GPX into my MRA online software then send it back to the Zumo, the mileage is identical to Basecamp. So the Zumo is doing something I can't figure out.

Any help is greatly appreciated.

[jfheath]

Welcome to the forum and thank you for your first post.

So the Zumo is doing something I can't figure out.

When you have the answer, please let us know !

In the meantime .......

'Faster Route' may be confusing you. It confused most of us, in that we belived from previous Zumos that it would aim to find a route that was faster than any other route that it calculated. Not so. Apparently, 'Faster' does not mean Fastest. Yes we knew that, I've been speaking english for most of my life, but sort of assumed that it was at least faster than the majority of routes heading to the same destination.

What it appears to mean is that the Zumo will prefer to use 'roads that are faster'. And if that means heading away from the obvious route to use a more major road to get to the destination, then that is what it appears to want to do.

My current theory - yet to be proved - is that if it can get to a major road faster than it can get to the next route point, then it will head for the major road - even if it means heading off at 90 degrees to the intended direction. But this is just a muse. Something that popped into my head, and which one day I will experiment with. But it is a reasonable working theory.

The other thing that you need to know

When a route is transferred from Basecamp to the Zumo the Zumo WILL keep the identical route that was produced by Basecamp. Providing the maps are the same version and that all of the tick boxes in Basecamp's Edit / Options / Device Transfer are all left unticked, and that the button to apply to all devices has been clicked (to avoid doing this for an old zumo that Basecamp has remembered). That remains true as long as the Zumo is not allowed to recalculate the route - eg by skipping a route point; by turning off automatic recalculation; by not allowing traffic reports to affect the routing; by not allowing u turns.

The trick is to make sure that you have your Via Points and your shaping point to be placed strategically. You don't need that many more with the XT, but if you mark a turning by placing a shaping point just after a junction at which you intend to trun right, then you can expect the XT to visit that point and immediately head you back to the junction to rejoint the faster road that you have just left. It is what it does.

I ignore all of the suggestions that tell people to place a lot of shaping points in the route so that the XT cannot alter it. It makes life really annoying if you have to avoid roadworks. I find that usually for any stretch of 'slower' road - if it is likely that the XT is going to head me to a faster road in the vicinity - that placing a shaping point one third of the way from where I joint it and another one third from where it meets a faster road is pretty good at sorting out most issues.

But there are lots of different ways of using navigating with the XT. One way is to convert your route in Basecamp to a track - the option is available by right clicking the route - and using that. Tracks stay put, and there are 3 quick and easy ways to use a track . All 6 methods are descibed here.

app.php/ZXT-P45

MyRoute App behaves differently depending which GPX format you choose. See here app.php/ZXT-P72

but in particular pages 72c and 72d

[meagvg]

Thank you so much for the reply.

I've read (and re-read) and bookmarked your tutorial. It's my go to reference.

I'm going to experiment with tracks a little more.
These are IBA rides I'm routing, so setting up mileage is critical.
Last weekend's ride showed 1535 on Basecamp, 1550 when the Zumo took it, and in real time ended up being 1522. This sort of thing drives me nuts.

Over my past few rides I've found that if the Zumo "over recalculates" distance, it's better than the alternative which would leave me short.
It's just a little unsettling when my Basecamp and Zumo miles don't match up.

Thanks again for helping me.

[Peobody]

I see discrepancies too but not to the degree the you see on the route you mentioned. Here is a comparison of the routes currently loaded on my XT:

BC 86 XT 88
BC 140 XT 140
BC 127 XT 129
BC 120 XT 121
BC 249 XT 253
BC 440 XT 441

A 15 mile discrepancy in 1535 is not surprising based on the above. It would be nice to have an explanation though.

I have never tracked actual miles.

[meagvg]

I have a feeling it might be that my workflow is faulty.

I build a route in BC, convert to track, then convert back to a route. Often multiple times if I alter the original route.
I do this to generate a high number of via points to pin the route, rather than individually placing those via points.

An import of KML from Google then track->route might be worth a try. I recall that worked well in the past.

Off on a cross country ride next week. So it's back to testing and hope to get it sorted before I head out.

[Peobody]

I have a feeling it might be that my workflow is faulty.

I build a route in BC, convert to track, then convert back to a route. Often multiple times if I alter the original route.
I do this to generate a high number of via points to pin the route, rather than individually placing those via points.

FWIW, I build my routes totally in BC. I drop waypoints on the roads I want to travel (adding sequential number prefix to the name as I go), then I select them all and use the "Create route using selected waypoints" function. I change the sequence if needed then review the route for actual vs intended, adding route points to fix as needed. Finally, I check to insure that all points are centered on the road (or in the correct lane) and change via points to shaping points as I think is appropriate. I then transfer it to the XT, import it, load it and compare it to my BC route. My routes rarely exceed 400 miles; I create one route per day for my long trips.

I also "fix" my routes but haven't settled on a standard way. For multi-day trips I will run each of the .trip files through the JaVaWa Trip Repair tool but for my last one-off route I started it and then saved it. That felt cumbersome, likely because it was my first time figuring out how to do it. It took awhile. I should have made notes. I suspect there are instructions on this forum somewhere, I just haven't searched yet.

[meagvg]

Thanks!
I like your workflow better than mine. It's certainly giving you more consistent results.
I'm being too "clever" with my process and it's likely creating compounding errors. Especially since I'm always revising.

[jfheath]

There is bound to be some difference.

I assume that the zumo measures the total of a very large number of short straight lines, which do not exactly fit the curve of the roads.

The bike on the other hand takes the largest curve route around any bend, making the recorded mileage shorter than the distance covered by the tarmac.

Then there are tyres. Over the life of the tyre, the tread reduces the total diameter of the wheel by 2%. Temperature and tyre pressure may also affect the diameter. So the distance recorded by the odometer different by 2%

2% of 1500 miles is 30 miles. So in theory there is a difference of what the bike would record between when the tyres were new and when the tyres are worn of 30 miles.

Who is to say at what point your odometer is recording accurately ?

The IBA should give an appropriate allowance for recorded mileage. It is probably already built in. You have to work out what the difference is between your bike and the satnav.

Before satnavs you might have used a piece of string to measure the route on a map, or a mini map measure trundle wheel. They would have accuracy problems too.

I assume that the IBA take your odometer reading as the definitive one ?

So I would think that you knowing how your odometer relates to your satnav mileage is the most important thing. I also think that going through different programs to plot your route is not helping.

Why not use BC and then use BC to create the track. There is no conversion error there. The track uses exactly the same number of track points in exactly the same positions as the points use in the route. I mean the ghost points - the route point extensions, not your vias.

Then transfer both to the Zumo and superimpose one on top of the other. The route may be altered but the track will stay put. Follow the track if the route differs.

Make sure you apply the mImport fix to prevent the RUT behaviour.

[meagvg]

I'm going to take all this good advice and go simple. Place waypoints manually as needed. Stay within BC which is where I'm most comfortable anyway.

My bike's ODO actually is about 2% off, which adds up over a long ride. Apparently the IBA is aware as they only use the ODO for a verification picture with receipt to prove you were located where you claimed to be. Their standard is to use Google maps to calculate the ride. That and Spotwalla.

When I've done those 1500/24 rides, it's depressing after a long day to see my Zumo show 1470 when I thought I was going to be at 1500+. So if the Zumo goes long after a route transfer, I guess it's better than miscalculating short.

I just really like when the numbers on the computer match those on the Zumo. Haven't got there yet, but I'm still working on it.

BTW, what is mImport fix and RUT?

[Peobody]

RUT = Repeated U-Turn. This is when you have left the route and asked for a recalculation but the XT repeatedly tries to to turn you around rather than navigating ahead. See this thread for a nice summary about it: viewtopic.php?t=2482

"mImport fix" is a fix for the RUT behavior (although I think this is the first time I have seen it called mimiport). There are several methods to accomplish it but the end result is converting a route so that the XT sees it as a Saved route instead of an Imported route. See this discussion: viewtopic.php?t=2323