Weird Routing Behaviour (2)

[FrankB]

But you dont get U-Turn request! So it could be different.

[jfheath]

@FrankB, did you skip a waypoint? The skip action gets mentioned a lot in discussions about the persistent u-turn behavior although I have lost track of whether it remains a component or has been ruled out.

Yes. I have seen that a few times. It is that behaviour which makes me suspect what is happening.

The 'track trip' behaviour is interesting. If you deviate, it's job is to get you back on track and it seems to do this by finding it's way to the closest point on that route. It helps if you first observe following a track. Load a track and say Go!. No navigation commands, but the xt plots a dotted straight line to the closest point of the track. Leaving the track completely intact.

Like this:



If you then plot a new track that is essentially 3 sides of a long rectangle, and convert that to trip- a 'trip-track' - and set off on that then you get navigation instructions. If you then deviate and head along the more direct 4th side of the rectangle, rather than the route which goes round the other 3 sides, you can observe very similar behaviour. It chooses the closest point of the (parallel) original route but this time calculates a way to get to that point along roads. Constantly updating as you ignore its instructions - finding a new closest point. In the picture below I am heading south in the direction of the arrows. The route is heading south on the parallel original route to the left of the screen.

Like this:




The new section of route from your current position to the closest entry point now becomes part of the actual route - continuing from the closest entry point along the original. It's important to remember that - the closes entry point splits the original into two parts, and 'discards' the section before the clsoeset entry point. It tags on the newly calculated section from where you are to the closest entry point.

But if you deviate in exactly the wrong direction - 180 degrees - the closest point to the new route is always behind you. Does that sound familiar?
The Trip-Track also gets stuck in a RUT in these circumastances.

So my suspicion is that certain operations performed by the XT use the routines associated with triptracks, rather than calculating to the next route point. I suspect that closest entry point and skip button use these triptrack procedures in order to calculate a route - rather than the one that plots a route to the next point. Which is why I think that a route does not get stuck in a rut if the Zumo has not recalculated the route - under those two circumstances. I have yet to find one.

Abandoning the route and then rebuilding the route on the XT screen, using the identical saved favourites will result in a route that behaves itself. This I think supports the idea that the XT has more than one method of creating a route. My suspicion is that after tapping Skip, or using CEP, a new route is built using a similar algorithm as the one used to create a track trip.

The XT is odd in my experience with the 590, in that it recalculates the entire route after pressing Skip, so any change like this will affect the remainder of the route.

All pure speculation on my part, but just thoughts based on many tests and observations.

[FrankB]

I drove a route yesterday and observed something that might be worth mentioning. If you start a trip on the XT and select 'Begin' the route from where you are to the beginning does not have the U-Turn behaviour. I was > 25 Km from the begin and I deviated 2 times from the XT proposed route. Both times there was just one U-Turn request, and then the XT calculated a new route.

Agreed: This is just one case. And it's not really a solution. But I think it adds more proof to the statement "Routes created on the XT dont show U-Turn behaviour"
Will think of a test case that reveals more.

@Peobody
Please forget this. I did a test today with a route that I am certain will go into a RUT. Makes no difference if you're driving the route, or if you still have to go to the begin.
Sorry, should have checked before posting

[Oop North John]

Has the u-turn madness been modified by Garmin? I had a small route with a via / waypoint in which it would repeatedly ask me to do a u-turn even when it would double the journey length. Same route now seems to recalculate sensibly after about three u-turns requests.

IIRC the SP3 took so long to recalculate if you went off route that the developers added in trying three times to make a u-turn so that it could catch up. After three goes, it then fully recalculated the route, so, maybe history is repeating itself.

[rbentnail]

But you dont get U-Turn request! So it could be different.

Oh but I do! When traveling to the start point (the end point of my mini-route) the XT wants u-turn after u-turn after u-turn rather than seeing a closer point of entry.

[jfheath]

I have not seen any difference yet.

It is important to know the difference between

1. A route that is simply asking you to perform a u-turn to get you the 'faster' way to the next point. Note that 'faster' doesn't mean 'fastest'. It seems to mean that it will take the major roads - even if it covers more distance and takes longer.
2. A route that is redirecting you to a missed Shaping Point or Missed Via Point: If you rejoin the route having missed a Shaping Point or two then when you join the magenta line it will continue to calculate to the next point ahead. However until you actually rejoin the magenta line it will still be attempting to get you to go back to the first missed shaping point. (You cannot miss Via Points in the same way though).
3. A route that is actually 'stuck' in a series of U turn requests. These are difficult to spot. Only if the distance time ahead is less than the time to go back can you begin to suspect that you may be in a RUT. Even then, you would have to eliminate road closures ahead as the cause, and you cannot do that until you have continued to the end !! However - there is a clue. If you turn U-turns off, the xt has to find other ways of getting you to go back. This usually means taking a roundabout or side road that will lead you back on a parallel road for a short distance.
   This detour off the main road is very visible on the preview map, and they become part of the route back. And I think that this is definitive evidence that the XT is no longer attempting to take you to the next route point. Attached are three examples of this behaviour. Click the image for a better view.
   
   The route back includes all of the places where it plotted a way for me to turn round. If it was plotting a route to a particular point, it would not include those loops. The only conclusion that I can draw from this is that it isn't trying to get me back to a route point. It is trying to get me back to the last point where it told me to turn back. Repeatedly.
   
   On the map showing Cracoe, the motorcycle is off the top of the screen. The satnav is wanting me to head south. The marked locations are where it attempted to use side roads to loop me back - and they are still part of the route that it has plotted for me to go back.

RUT loop 1.jpg (81.47 KiB) Viewed 520 times

RUT Loop 2.jpg (37.29 KiB) Viewed 520 times

RUT Loop 3.jpg (82.35 KiB) Viewed 520 times

My last conversation with the Technical Support team was just before Christmas, then it went quiet. No repsonse. I didn't mind too much, this is taking a lot of time and I didn't have the chunks of time available to chase it up until just recently. @stu contacted the Garmin support on Twitter, and I provided a link to the reference number and that prompted a response from the member of the team who had been so helpful in trying to get this issue nailed down. They contacted me and will get back in touch in the next week or so to move it forward. They also said that they would take a look at these forum posts to get a feel of how widespread the issue is.

[jfheath]

@FrankB, did you skip a waypoint? The skip action gets mentioned a lot in discussions about the persistent u-turn behavior although I have lost track of whether it remains a component or has been ruled out.

Sorry - late spotting this - I have been busy. The association with Skip is something that I have made.

I think that some routes behave perfectly nomally. I have created in points in Basecamp and transferred them to the XT. I have built a route on the XT using those saved Waypoints (Favourites / Saved). I have followed the route and then deviated, and the route immediately recalculated int he direction I was going. Later I deviated again at a place where previously the RUT sitautaion had always occurred. The XT recalculated ahead immediately. IT behaved perfectly.

Having had that success, I immediatley rode back before the offending detour. Stopped the route, deleted it and then re-built it on the XT screen. This time I selected Closest Entry point - as I had already passed the starting point. It picked up the route, navigated me ahead and when I deviated at the same junction it refused to calculate ahead.

I have done exactly the same route with an additional route point after the start which I skipped. When reaching the same places, I deviated and got stuck in a RUT.

I have had Basecamp routes behave themselves. Skip seems to be the trigger that changes the nature of the original route - Skipping casues the entire route to be recalcualated on the XT. And after that, any deviation seems to result in getting you back to the magenta line rather than calculating the best way to the next route point.

The other day, I thought that I was updating Express. When I returned to the Zumo, it had done something else which required 3 restarts. I do not know what. The software is the same veriosn number, none of the other updates listed in Express had been installed. But at one point the XT mentioned new software and needing to reboot.

I might need to do some further testing to see if behaviour has changed.

[Oop North John]

My observation of the 3 u-turns then routes sensibly is based on a route that previously it would take me within a couple of miles of the destination, still wanting me to u-turn, and do about 8 miles back along the same roads I'd come along.

[rbentnail]

My observation of the 3 u-turns then routes sensibly is based on a route that previously it would take me within a couple of miles of the destination, still wanting me to u-turn, and do about 8 miles back along the same roads I'd come along.

It acts like once it has picked a point to join a route at closest entry, it is unable to realize that it can change it.

[Peobody]

My observation of the 3 u-turns then routes sensibly is based on a route that previously it would take me within a couple of miles of the destination, still wanting me to u-turn, and do about 8 miles back along the same roads I'd come along.

I sure hope it's fixed, but what would have fixed it? Wouldn't that take a firmware update?