Recalculation - what gets used from the gpx file?

[tombarrington]

This topic has been covered many times but my searches don't seem to land on a conclusive answer. I'm running an XT and using BaseCamp for planning daily routes. They typically have several non-alerting shaping points and a via point or two as reminders for fuel. I'll have that day's track showing under the route and Recalculation set to Prompted.

If I do allow a recalculation (which is rare), what gets used for the remainder of the route? To me, it should be the remaining shaping points and via points. However, I think I've seen mention of just the via points or just the destination. Knowing the answer might cause me to be less hesitant to recalculate. TIA.

Edit: I also use TripManager to eliminate RUTs.

[Peobody]

If I do allow a recalculation (which is rare), what gets used for the remainder of the route? To me, it should be the remaining shaping points and via points

It is. The recalculation just calculates a new route between the route points. If , during route planning, you have excelled in your anticipation of what the XT might do if it recalculates, then you might be lucking that the recalc matches the original route. FWIW, this used to really frustrate my but I have resigned myself to restarting the route if the deviations created by a recalc are severe enough that restarting is a better option than manually following the track line.

Worthy of comment here is that I store the originals on the SD card, where the XT will never modify them. This allows for a re-import should I do something bone-headed like inadvertently editing the route with the XT.

[tombarrington]

Thanks, @Peobody, this is what I hoped I would hear. I recognize that the Zumo may find a route between two shaping points that is different from what I intended but I try to minimize this potential when I do my initial planning. I store my originals on the SD card, as well.

Personally, I'm not a fan of following a track so I, too, would restart the route if I strayed to far from the original.

[jfheath]

The XT2 behaves differently from the XT1 in this regard.

The XT1 will calculate routes from route point to route point - via or shaping, but the route leaving or entering a shaping point is likely to be very different if that point is set as a Via point.

As a one of example, A route may be plotted to visit a shaping point as a detour, and then double back to continue on a faster route. Whereas if the same point is set a a via it is less likely to do that. My ‘explanation’ is that it works on segments (ie the part of a route between Vias). Having reached a via, a new segment starts - it isn’t going to double back.

With a shaping point, its faster route between via points will use faster roads even if it takes longer time, and doubling back when that logic is applied at the shaping point, makes sense. Leave the faster road, visit the shpt, double back to the faster road.

The XT2 is different. It ignores the shaping points and plots a route between vias and then ‘something’ decides that the shaping points are to be moved onto the route it has plotted. There does seem to be a limit to how far it is prepared to move a shaping point though. My current observations suggest somewhere probably less than a mile. But I haven’t tried to pin it down precisely.

But the XT2 doesn’t seem to do that by itself. I believe that Tread needs to be involved either at the planning stage or at the synching stage. I’m not sure whether the XT2 alters the route when it is importing a gpx file without Tread being involved. I think that it may, but am not 100% sure. I have forgotten. It certainly doesn’t do it with a TripManager transferred route.

Displaying the track of the original route as well as the route is a good option. Modify the theme to make tracks slightly wider so that the edge peeps out from under the track. Any change in the route from your original is obvious. Assign them to the same collection and make only that collection visible. Black tracks show up well

[Peobody]

With a shaping point, it’s faster route between via points will use faster roads even if it takes longer time, and doubling back when that logic is applied at the shaping point, makes sense. Leave the faster road, visit the shpt, double back to the faster road

Hmmm. I have never noticed the 'faster road' preference of the XT1 change based on via or shaping. If there is a faster parallel road, it will backtrack to get you on that faster road even if it triples your distance and doubles your time. I don't think I have ever seen it not do that regardless of whether the point visited before the backtrack was a via or shaping. This is a moot point though as pertains to this conversation. If it recalculates, it is going to create a new route that visits all remaining shaping and via points. The unknown is the roads it will choose. Once you see what it came up with, you can then decide to follow the new route, manually follow the track line (if you have one), or restart the route.
@jfheath, I sprinkle via points throughout my route so that in the event of a restart, I have one somewhere not too far ahead to select as an entry point rather than relying on 'Closest Entry Point". If someone is past several vias and does a restart, will using CEP create a route that ignores all prior vias, or will it create one that goes to the first via and then follows the ghost points? (assumption: Basecamp was the planning software)

[jfheath]

Thanks @Peobody

Not a moot point for me. Perhaps I didn’t explain properly.

Three point route - A B C. All vias.. Middle Via is designed to keep the route on a particular road, rather than taking a faster road over to the left. B puts a slight kink in the route.
The Zumo will keep the route as intended. Ie going A to B is the ‘fastest’ route. Going B to C is the ‘fastest’ route.

Change B to a shaping point.. A to C ‘straight line’ route between the two is the best option and makes sense. B is still visited but now it is routed as a detour from the faster route A-C.

Your second comment, when choosing Closest Entry Point the Zumo XT1 spots the place on the original route that is closest to your current position. It deletes the original route before that location and builds a new section of route from your current location to that closest point. The remainder of the route - vias, shaping and ghost points remain intact.

Restarting the route in this way is a good option, but the plotted route must be checked on the preview map. It has been prone to making odd decisions.

At one time I proved that this was due to two things - not allowing U turns and the satnav not knowing which direction the bike was actually facing. Note that changing permission to allow/disallow u turns when a route is running will recalculate the remaining route. I haven’t tested it recently, but still check.

The route chosen as the CEP may be based on straight line distance. I suspect, but don’t know. It does not calculate a route to the nearest via or shaping - it heads for the actual nearest location on the route. Probably doing the maths based on ghost points.

The point selected may therefore take you back to a point that you have already ridden - so the check of the preview map is important. It doesn’t look ahead, it looks for closest. Use of CEP needs to be used carefully if navigating a fig 8 route or a long narrow oval. The closest point may be on the return leg.

I have not checked any of this for the XT2 except to say that mImported fixed routes seem to behave in the same way as XT1 with respect to CEP.

I THINK I have some links to the above. I’ll come back and post them if I can find them. I certainly have a document thoroughly testing CEP on the XT1 that you are welcome to.

[jfheath]

Regarding the first comment - I couldn't find the images on here that I'm sure I posted - so it seemed quicker to reproduce a similar test.

3 points created on the XT1 screen and saved as Waypoints.

First route was created and the middle point was set to a shaping point.

XT1 3Pt Route with Shaping Point.png (331.17 KiB) Viewed 488 times

I then changed the middle point to a Via Point ** and the route changed.

XT1 3Pt Route with Via Point.png (269.53 KiB) Viewed 488 times

Change it back to a Shaping point it changes back to the same as the first image.
Change it back to a Via the route changes to the same as the second image.

** Using the XT1/ XT2 /595 screen to change a via to a shaping point often moves the shaping point slightly. But it never changes position if you change it from a Sahping to a Via. To minimise the effect of this I made sure that the point was A) A waypoint B) Placed on the location of a known placename - ie Cracoe.

But it illustrates the fact that the choice of a shaping or a via does affect how the route behaves on the XT1.
Although I expected the change in route to be the opposite way round !

[Peobody]

The point selected may therefore take you back to a point that you have already ridden - so the check of the preview map is important.

I experienced this early in my time with satnavs, my XT being my first. Fortunately I had the presence of mind to look at the preview map before starting out.

[smfollen]

@jfheath In case it helps, regarding how CEP behaves, viewtopic.php?p=20805#p20805 is the thread with your test results and my mostly consistent theory of what CEP was doing on the original XT. It seems to be similar on the XT2, but I have not done any complete retesting.

I have since then learned from @FrankB that route points (via or shaping) located at intersections can confuse CEP, even when those points are much farther down the route than the CEP starting point.

Of course points in intersections can have other consequences too.

[FrankB]

I have written down some experiences here: https://frankbijnen.github.io/TripManag ... tions.html

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