I''ll respond to your reply later
@epv and continue with my essay.
2. A GPX file is created and IMPORTED to the XT
This includes transferring via the Drive App.
Here is where the fun really starts. In some situations (not all) if the route recalculates, the behaviour of the route alters. One of those situations is after you have pressed Skip. The full route is
always recalculated by the XT and it
always changes the subsequent behaviour. I should qualify my use of the word 'always'. Always refers to the many tests that I have carried out.
After Skip, the route will probably look the same as before if the Zumo calculated the route after it was imported. Basecamp routes and MRA gpx v1.2 are different - they send the Zumo the exact plot of the route with thousands of invisible route points - one every few metres on twisty roads. The XT does not recalculate those routes on import unless the maps are different - or in Basecamp there is an option to tell the Zumo to recalculate the route.
That means that if the XT
does recalculate such a route, the result is likely to be very different from the original. It will still pass through all of the shaping and via points, but it will probably head for faster roads if it can. That may mean visiting a shaping point and then turning back to a faster road. If you load a track of the route as well as the route itself and show it on the map in a different colour (black stands out), you can spot whether the route has been recalculated.
Link Page
A well behaved 'saved' route will always treat the next route point as its target and calculate a route to get you there. So if you are forced to deviate, you know where it is heading - your next route point.
If skip has been pressed at any time, the route will have been recalculated - even if it didn't actually alter the route. But it may now head for faster roads if it gets half a chance - thats what the XT does. But the way that the route behaves will now change.
It no longer treats the next route point as its target.
It treats the route itself as the target.
This is not a problem if you stay on the route. But if you are forced to deviate it can become a big issue. Or not.
Let me explain those 'target' sattements. Suppose that sometime (any time) after pressing Skip - you have been forced to leave the route which is heading north. Perhaps a Road closure. You are now on a road that is 2 miles to the left (west) of your original route but still heading north.
A 'saved' route would find a way to get you from where you are to the next route point. That route point is what it is heading for.
An imported route will try to get you to the closest point of the original route. So its target is somewhere ahead on the original route - not the route point. So it will plot a route to take you back to the right (east) at the first opportunity.
That is pretty impressive. Each time you ignore its instruction, it calculates another way to get you back onto the new closest point on the original route - by finding another road to head you east. You ignore it until you think you've gone far enough to get past the road works and then may decide to take its latest suggestion. It works. It works surprisingly well.
But here is the behaviour which makes no sense at all when you are on the bike. While you have been heading north on the parallel road, you have actually been getting closer to the next route point. It makes sense for you to carry on in that direction. You are thinking that is where it is heading for - the next route point. But the behaviour of the routing has changed - becasue the behaviour of the routing has changed. The next route point is not the target. The traget is still the closest point on the original route. So if you are now 3 miles from the route point, XT is trying to get you to head 2 miles to the east to get to the original route and then(say) 3 miles to follow the original route which just happens to pass through the next route point.
That behaviour is very clever.
To describe how to see this behaviour in action, jfheath wrote:If you want to see it in action, then create a track of a route using Basecamp or MRA. Load the track into the Zumo and use the spanner option to convert it to a trip. The new 'Trip' will appear in trip planner, and you can load it just like any othe point-to-point route. Except it has no shaping points and no via points except a start and a finish.
It issues instructions at every junction and it will never recalculate the original magenta line. It just 'deletes' the original that is behind you. So if you have to deviate from the route onto a road that is running parallel but 2 miles to the left - it does the same as described before but it is now a bit more obvious. The XT finds the closest point on the original route ahead. It sets that point as its next target and plots a new section of route from your current position to that target. Any section of the original route that has been missed out is deleted.
If you want to see the XT continually spot the closes point when you have wandered off a track - simply load the track and select Go !
See this link
You have to try the Track-Trip method to see how good it is, but it has a couple of serious issues.
- If you are following a long narrow circular route - elliptical - in a clockwise direction, left side first heading north and you deviate to the right from the plotted route - it finds the closest point of the original. It may find the route heading south and miss out most of your tour.
- If you turn up a road where there is no closest point ahead, the only point that it can find is behind you. It plots a new section of route to take you back, and that becomes the new route. Ignore it, it does the same. The closest pojnt of the current route is always just behind you. It is a situation from which it cannot escape - not until you reach a point where you are closer to joining the original route than you are the point that is just behind you.
It is easy to understand what the XT is doing with a track-trip (my term for a track that has been converted to a trip). But that is exactly the behaviour that you see if you have pressed skip and some time later you deviate from the route. I said that when you press skip, the nature of the route changes. It seems as though it has started to use the Track-Trip algorithm.
As a consequence of that, the route points are largely irrelevant. The route has been calculated to go through all of the route points in the correct order, but they are no longer the priority. Getting back to the closest point is the priority.
In a
'Saved' Route as in my first scenario - you can use the Skip button to see which point the XT is heading for next. It says - do you want to skip 'Coffee Stop'. Very handy. Select No. But that is useful for checking where the satnav is trying to take you. Each time you psss through a point, it removes that point from its list.
In this new scenario with the imported route, the route points remain in the list. It doesn't recognise that you have passed through them. But that's ok. After pressing skip,
you are no longer following a point to point route. It seems that you are following a track - trip.
One other side effect of this is that although the route will take you to the route points, because that is where the route was plotted, the route point itself has become irrelevant, and as you drive past the road end where you were supposed to turn off to visit a route point, the route point disappears, You have not followed the route so it recalculates to find a new way to get to the route which is immediately under your front wheel, and the route behind you is deleted.
In this next video I am carrying out the same test as before. The route this time has been imported and I included a route point very early on in the route - just so that I could skip it. Now the nature of the route has been changed. It is behaving like a Track-Trip would. When I deviate from the plotted route, it is only concerned about getting me to the closest point. Not to the route point.
So I am at the roundabout. In the first 5 seconds you can see the sahping point near addingham, and that I am being instructed to take the second exit of the roundabout. At (0:13) I take the third exit, and the route recalculates as it did in the previous video). But when the screen zooms out, the shaping point near addingham no longer exists. There is no way to turn round on the A65 that I am now on, so I have to go tot he next junction - but it doesn't bother to try to take me back. The closest point of the route isn't back in addingham - its up ahead at the junction. It looks as though it is trying to take me to the next shaping point - but it isn't. That just happens to be on the route.
The video stops as the Via Point in the middle of the field comes into view. It begs the question - what happens next. I have videos of that for a Saved Route. It wants me to go into the field to visit the point. I go past. It wants me to go back. In short - you must visit Via Points. That means that they have to be carefully placed. If you place them slightly off road and the satnav expects you to trun left before reaching it - it doesn't spot that you are close enough to have visitied it. Go past it with it recognising that fact. and the satnav is forever trying to get you to go back there.
But this is what happens at the same point if the nature of the routing has changed. (I pressed Skip)
The Zumo no longer cares about visiting the VIa Point - it is finding the closest point of the route - and that is up ahead. Notice that it deletes all of the route that has gone before.
There must be other circumstances when the route changes like this. Other's on the forum have come across it. I have not been able to prove or disprove any of them. It could be quite useful in this mode. But it is not the picture that is in you head - unless you know about it - and that will be confusing becasue you think you know what it should be doing.
Well - now you do !
Section 3 follows
