guiri wrote: ↑Sun Jan 08, 2023 5:55 pm
Hmmmm Garmin!
I took the XT for it's maiden voyage today, and whilst the overall experience was positive, I got this weird routing behaviour near home.
There were a few different triggers maybe...
I'd already started navigation half way into the route (after a coffee stop).
I restarted the navigation having decided against the final coffee stop of the day (and skip waypoint didn't work as expected).
I didn't follow the suggested rerouting due to traffic and stuck to my original plan (I had recalculate on automatic though).
I got u turn request after u turn request. I got the impression that it was trying to take me back to where it thought I should go due to the traffic, rather than just reroute from my current position (because it didn't seem to realise that I was getting closer to home and was on a sensible road).
I didn't think to check the edit list, I'll do that next time!
This is a behaviour that I have reported twice - and which I have mentioned on this site a few times. The 1st attempt resulted in someone senior dealing with it who was very helpful. I gave a lot of evidence, convinced them of the fault and it was passed ont o software development. Nothing since then.
That was about a year ago, I guess. The I discovered another fault - that of the broken track log. I use the track logs a lot as a historical record of where we have been, stayed and roads that we have ridden and to have them broken into sections of a minute or less was really irritating. So this time I have someone who seems much more determined to sort it out. I think mainly because of the quality of evidence that I have sent - but also they were intrigued by its apparent association with the 'Go back to Old Kent Road' behaviour - which was apparently something new. They must get a lot of people who blame the XT, blame Garmin, blame the maps. I don't I look at it as a problem that I don't know the answer to and until I do I'm quite happy to consider myself as one of the causes.
Whatever, they have latched onto this, partly becasue the evidence I have sent is complete and explained - but they couldn't reproduce it. So in order to elimintae my XT as the issue, the wanted mine in their hands to see if they could get it to do it. They sent me a bran new unit in its place, and the first thing that I did was to go out and get it to go wrong again. That was 22 December, pouring rain but not icy. It is amazing how much grip there is aon a wet road when you have ridden on icy roads.
I've discovered a few things from which I have a hypothesis. But it is far from complete.
The use of the Skip facility to remove a via or shaping point from the list certainl has an effect. That causes the entire route to recalculate. (Beware MyRouteapp users who export the route using GPX v1.2 format - as it strips the shaping points from the route, so the recalculation will not go through them).
Uisng Closest Entry Point also seems to have an effect.
In most of my tests if I have done anything that causes the XT to recalculate the route on the fly, any subsequent deviation seems to result init refusing to calculate a new way to get to the the next route point, and it insists on going back.
On the other hand, if I choose simply a destination having selected Where To ?, then the route behaves perfectly sensibly. So far anyway - I haven't tested that a great deal yet.
But I've seen other odd behaviour too.
There are a few things that you can do:
Simple things first:
Turn off automatic Recalculation. That means if you deviate, the XT will not change your route. It will go quiet until you rejoin the route.
Make a track of your route (you can do that in Basecamp quite easily. Transfer both. Show both on the map. The track will not alter.
Create a track and ask the XT to navigate it. (with / without auto recalc turned on) . The XT will navigate you along the magenta line. If you deviate it will plot a straight line to show you where the nearest point on the route is. Its up to you to get there.
A bit harder.
Create a track and ask the XT to convert it to a trip. This navigates like a route, but if you deviate it will do what the XT does when navigating a track and find the closest point from your current position to the route and then find a way to get you to that point.
Neither of these methods show any route points.
A bit different.
Think about where you might want to force the XT into taking a particular road. It isn't very helpful adding lots and lots of shaping points as they can become more restrictive if you are forced to deviate. But adding a couple which are strategically placed will certainly help.
PArt of the problem is to do with the fact that when the XT recalculates, it doesn't find the fastest route. It finds a route which uses faster roads. Even if it takes longer and is a much greater distance.
So if you have a couple of Via Points that you know your really want to pass through (eg coffee stops) then putting a couple of shaping point in between will help. But don't put them on junctions. Put them part way along a road.
Example. If you have a nice 'A' road running in roughly the same direction as the a motorway, then you have to stop the XT from taking the motorway (don't say put an avoidance in, otherwise I will have to think of anothoer example, and this example is easier to understand !).
If you put one shaping point part way along the A road - to force the XT to go onto the A road rather than the motorway, then all the XT will do is come off the motorway at (say) Junction 123, visit your shaping point and then rejoin the motorway at the same junction - 124. So if you try to prevent that by putting the shaping point closer to junction 124 - it will simply stay on the motorway and come off at Jn 124, visit the point and then go back on the motorway.
So you think aha - and place the shaping point on the A road - roughly equal distance from two motorway exits 123 and 124 - then there is a pretty good chance that the XT will come off at one of the junctions visit the point and then go back to the motorway at the same junction. The lure of the faster road seems to be quite strong.
So a better strategy is two use 2 shaping points. Split the A road into 3 equal parts. Put a shaping point at each point. It has to visit the shaping points in turn, but now it is much harder for it to make the motorway a better option. It would have to come off at Jn 123, visit the first point, go back to Jn 123 up the motorway to Jn 124, off to visit the 2nd shaping point an then back to Jn 124. Much. much longer. It doesn't always work but it stands a better chance then the other two, and it is much better than adding a lot of shaping points - which are a real headache if a road is closed or there is an accident or a massive queue.
You have to look at the proximity of 'faster roads' - if there aren't any, then you might not need shaping points at all.
Things that don't help: Turning "Allow U turns" off. It just makes the XT go quiet for longer periods until it can find a road to take you back.