Weird Routing Behaviour - Major Success.

[jfheath]

Remember the Repeated U Turn (RUT) behaviour, which crops up if you skip a route point early in a route and then later deviate from the plotted route ?

What happens is that it repeatedly tries to get you to go back to the place at which you deviated. And the track log is broken at each demand to turn back.

Right. Well today I carried out the same test with a route that I had tried and documented 3 times before, each with the same RUT result.

And it worked perfectly

That is, at each deviation, it immediately calculated a new route ahead;
Or it asked for u turns for a when it was obviously quicker to turn back, but recalculated ahead and then that became faster;
Or it immediately calculated a new route to get to the next route point, typically heading for faster roads.

And the track log was unbroken.

In other words, this route behaved perfectly.

But I had done something different to create the route

I used Basecamp to place 5 flag waypoints in the same place as the shaping points in my previous tests.
I transferred these waypoints to Favourites (Saved) and used the XT trip planner app to create a route
All of the waypoints were set as Via Points.

I have suspected for a while that routes created on the XT would work correctly, but this is the first time that I have tested it with a route that has always displayed RUT behaviour.

I've now got to find out if it is the Waypoints, the Via Points, The Basecamp route that has an impact - or the couple of system updates that have been applied recently when loading Express.

Meanwhile, tech support are inundated, but the engineer keeps finding time to work on this and has been able to reproduce the behaviour under simulation, and is updating me at the end of each week with progress.

[FrankB]

@jfheath
Hi John. I am not surprised by your findings. This confirms my findings of Febr. 15. See attached Word doc. That is not to say I don't appreciate your efforts.

What did surprise me was that the route/trip created on the XT, then sent to Basecamp/PC, and then sent unmodified to the XT again DOES show RUT.
Have you tried something simular?

[jfheath]

Thanks @FrankB I had noted your previous results, and had observed previously when I abandoned one test route as I was obviously stuck in a RUT, and rebuilt the route using the stored Favourites, that it behaved 'as it should'. I reported that finding to the support technician. So I suspected that this route would work perfectly.

But I wanted to perform an identical test to one that had failed before and which I had documented, and then systematically change one thing at a time and find out what makes it stop working.

Then I could start to pin it down.

I haven't actually transferred a route back and forth like that - not for testing a RUT. I did look at that when we were investigating the subclass field to see if we could work out if that changed. But not for on-road testing.

I have previously concluded that ad hoc Vias, ad-hoc Shaping, Waypoint Vias and Waypoint shaping makes no differenc in my previous tests to the RUT behaviour. I need to go back and look at my notes - I may not have to repeat those tests.

I have been thinking that it is a Basecamp issue - or an issue when transferring / importing. The latter is more likely as we know that the process of transfer and import changes the key route points. Perhaps it also changes the nature of the route. I think it shows the beahviour of a trip-track.
But I am a bit off proving that yet.

@Stu has mentioned previously that the same behaviour has been observed with routes prepared on MRA - which might point to the import behaviour.
However routes prepared on MRA do not seem to have the names of their route points changed.

[FrankB]

I have been thinking that it is a Basecamp issue - or an issue when transferring / importing. The latter is more likely as we know.....

I suspect also transferring / importing.
All trips that you find in the trip planner, be it saved, or imported, are stored in "zūmo XT\Internal Storage\.System\Trips". Filenames have extension .trip.
When a Route/GPX is imported from Basecamp, or whatever source, it has to be converted to this .trip format. This is a binary format, so not easily human readible.
If we could pinpoint the difference between a saved trip on the XT, and an imported trip from Basecamp, that would be interesting. Alas I have not found documentation of the trip format.

Hex dump of a portion of a trip file.

trip.jpg (352.32 KiB) Viewed 7374 times

[jfheath]

The RUT behaviour is odd though.

How does a route behave in different circumstances if a route point is skipped and a significant deviation from the plotted route is made?

RUT if the route has been created in Basecamp.
RUT if the route has been created in Basecamp and force to be recalculated by the XT
RUT if a Direct Route is sent from Basecamp (St lines) and is then recalculated by the XT
OK if the route has been created in the XT using Waypoints (sent from Basecamp).

It does the same whether a BC route is sent to the memory card or to Internal Storage.
It does the same if it is created as a GPX file in BC and then placed on the SD card (ie no transfer).

[FrankB]

On the XT Trip planner trips can be under 'Saved', or 'Imported'.
I have to test it, but I strongly believe that 'Saved' trips have no RUT, and 'Imported' Trip do have RUT.

3225.png (67.1 KiB) Viewed 7347 times

By looking at the the .trip files with a hex editor I found a flag named 'mImported'. It corresponds with trips 'Saved'/'Imported' in the trip planner. Could that be the flag we have been looking for?

This is screenshot of a quick & dirty program I made to display the various info in the .trip files:

Dump trip.jpg (117.92 KiB) Viewed 7347 times

[danham]

@FrankB,

Am I correct that the only way to create a Saved Trip is to do it on the XT itself?

-dan

[FrankB]

@danham
Hold on. I am about to post my findings of this morning. I'm quite happy with them...

[jfheath]

I have never noticed the Saved / Imported heading before. That is because I rarely have the two types together on the same device. If I am testing something, I don't want to mistakenly pick up the wrong file.

So that is a good catch.

And yes - The routes that I created for my last successful test were created on the Zumo screen.

The routes that were transferred (into temp.gpx) and then imported are all the ones that are under the 'imported heading'.

All of the routes that were placed directly into Internal Storage as a gpx file have to be imported and then appear under the imported heading.

Both the XT created and the Imported routes appear in the Current.gpx file.

[FrankB]

Very promising finding

This morning I did the following test.
- I opened a route in Basecamp that I was sure to get me in a RUT.
- I duplicated this route and renamed it to 'original name' patched.
- I then had 2 identical routes that I both sent to the XT.
- Once imported on the XT they were both under 'Imported trips'

32142.png (65.11 KiB) Viewed 7306 times

- I then copied the .trip files from the XT '.System\Trips' to my hard drive.
- Using a Hex Editor I changed the trip named 'patched'. I changed the byte that defines wether it's an Imported or a Saved trip.

HexView.jpg (247.3 KiB) Viewed 7306 times

- Copied the files back to the XT in the same folder. (Overwrite)
- After rebooting the XT the Patched trip was listed under 'Saved trips'. (That proved that I modified the correct field)

3112.png (71.82 KiB) Viewed 7306 times

- After that I actually drove the trip. And guess what? It behaved perfectly

Now what can we do with this info? I don't believe anybody would want to use a hex editor to change imported trips. I could write a small program that will make the modification, but it would be for testing purposes at best. Anybody interested in such a progam, send me a PM.
But I do think this is valuable info to share with Garmin support. @jfheath Agree?

@danham You're question: 'Am I correct that the only way to create a Saved Trip is to do it on the XT itself?' is basically true, but using a hex editor I am able to turn an 'imported trip' into a 'saved trip'.

I will do some more tests, to make sure this was not just a lucky shot.

Edit: I did some hacking/reverse engineering on the .trip format and for anyone interested I'm willing to share the info. Send me a PM.