Weird Routing Behaviour (2)

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Fourbears
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Re: Weird Routing Behaviour (2)

Post by Fourbears »

Here’s an interesting routing by the XT. Today I was going to Southall in London and had used MRA to plot the route. I deliberately left out some shaping points in London as traffic can be a nightmare and the XT usually deals with that. But today it took me to number 15 on the image then took me via the yellow line to number 16! As I was a bit geographically displaced at the time I didn’t realise it was taking me away from where I wanted to be! It presumably thought that was quicker than the MRA route but who knows? 💁
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Re: Weird Routing Behaviour (2)

Post by Stu »

Fourbears wrote: 03 Jul 2023 17:43 Here’s an interesting routing by the XT. Today I was going to Southall in London and had used MRA to plot the route. I deliberately left out some shaping points in London as traffic can be a nightmare and the XT usually deals with that. But today it took me to number 15 on the image then took me via the yellow line to number 16! As I was a bit geographically displaced at the time I didn’t realise it was taking me away from where I wanted to be! It presumably thought that was quicker than the MRA route but who knows? 💁
IMG_0094.jpeg
Did you use gpx 1.1 or 1.2?
Fourbears
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Re: Weird Routing Behaviour (2)

Post by Fourbears »

1.1 as 1.2 doesn’t work as it strips out all the points and produces straight lines. Been there done that!
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Re: Weird Routing Behaviour (2)

Post by Peobody »

Fourbears wrote: 03 Jul 2023 17:43 As I was a bit geographically displaced at the time I didn’t realise it was taking me away from where I wanted to be! It presumably thought that was quicker than the MRA route but who knows?
That is what it looks like to me. The 'Faster' option seems to select roads that have the highest estimated speed without any analysis of time. It can be absurd how much longer in distance a resulting route can be.
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Fourbears
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Re: Weird Routing Behaviour (2)

Post by Fourbears »

And just to help it also did this after point 17 to get to point 18! I abandoned it after that as I was fed up of traffic and took the route home that I had taken there.
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Re: Weird Routing Behaviour (2)

Post by Stu »

Fourbears wrote: 03 Jul 2023 18:35 1.1 as 1.2 doesn’t work as it strips out all the points and produces straight lines. Been there done that!
Yeah my first thought was that you may have used 1.2
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Re: Weird Routing Behaviour (2)

Post by jfheath »

The advantage of 1.2 is that although it strips out the shaping points, not the via points though (hand icons), it keeps the gpx description of the entire route line that has been plotted.

IF

the maps are treated as being the same on MRA and the XT

AND

the XT is not allowed to recalculate

AND

you dont choose closest entry point, or press skip

Then the XT Will follow the same route that was plotted on MRA. If you deviate from the plotted route, the XT will go quiet, and if you rejoin after a missed Via Point, it will never say anything again. You might be on the magenta line, but not in the same section of the route.

v1.1 keeps all of the shaping points and via points, but it does not have any info from MRA as to which roads were followed by the plotted route. The XT has to calculate those.

From my limited observations, I have never spotted the XT recalculating the route as if the maps were different.

---------

The yellow loop does not surprise me at all.

3 National speed limit dual carriageway roads will trump the shorter, faster back roads.

With the XT, the algorithms seem to want to reduce the amount of processing, in order to improve response. so if it can use 'faster roads' to get closer to the next route point, thats what it does. No more searching / calculating.

I suspect - but cannot know - that there may be more external influences to do with avoiding villages, rural roads, reducing noise and air pollution which are demanding the selection of routes that help to achieve this.

There is also the use of OSM mapping - something towards which anyone can contribute. I have seen that some local routes have recently acquired changes to the maps which have no corresponding road changes. eg Speed limits, bollards. Hmmmm. I can only speculate.
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Re: Weird Routing Behaviour (2)

Post by Fourbears »

The second one I am not surprised at either as MRA and the XT do route slightly differently and the yellow loop was likely to be quicker. However on his route my first point was about 1/2 mile from where I started so I chose to navigate to that first (as per your tip @jfheath) so the rest of the route was as I had planned. I knew that things might go a little awry after point 15 as I had deliberately not put points to see what the XT did. I just didn’t expect it to take me so far away from my destination at point 16! Having said that riding in/around London is a nightmare anyway so who knows which way was quickest!
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Re: Weird Routing Behaviour (2)

Post by mike_walker »

Just as another aside. I reset my XT the other day as my routes weren't being transfered to the device via the Drive app. Don't know why as it said they'd transferred but nothing was appearing in trips (I think there must've been a corruption in the route maybe?). Anyhow, the XT also did an update and I needed to re-enable the .system folder but holding the speed circular button didn't work (although it had the first time I enabled it a while ago). I got to the menu a different way - holding the top right hand corner of the screen after clicking on the volume icon (thanks to some random bloke on Youtube for that).
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Re: Weird Routing Behaviour (2)

Post by FrankB »

mike_walker wrote: 04 Jul 2023 17:13 Just as another aside. I reset my XT the other day as my routes weren't being transfered to the device via the Drive app.
It is a side note! Not related to routing. But here are my thoughts on the drive app.

If the communication between the XT and the Drive App seems to hang, you can start by resetting the Drive App, if that fails you can always reset the XT as a last resort.

In short, for Android:
- Disable Bluetooth.
- Go to Settings, Apps.
- Locate the Garmin Drive app.
- Force stop. Clear the cache
- Enable Bluetooth.

See also this post:
viewtopic.php?p=14394&hilit=drive+app#p14394
In this post also the option to reinstall the Drive App and pair again to the XT is mentioned. When you do that dont enable Garmin Explore, unless you really need it.