The answer, I think, is this.
The file we were provided with contained a track and a semi-corrupted route, created in My Route. I use the word ‘semi-corrupted’ as it was straight lines. When the semi-corrupt route file was recalculated in BaseCamp, the route offered up differed from the track. For any investigation thereafter, it was necessary to rely on the track as the correct definitive article.
BaseCamp tells us that the track is 163 miles in length, so we know that any route version must be near enough 163 miles long, too. We also know that the track has certain portions where the route version varies. An example of this would be at Blewbury, where the track turns north, left off the A417 to pass along the B4016 before turning right to pass through Aston Tirrold and South Moreton, to join the A4130 at Wallingford, where it turns right. In addition, we know there is a single shaping point (created in My Route) a little way along the B4016, which forces the route to that point. More importantly, there are then no more shaping points until very near the end on the A4155 between Medmenham and Marlow. In other words, there is nothing in between the shaping point on the B4016 and that on the A4155 to shape the route over several miles. Garmin, in common with other GPS devices, relies on strategically placed shaping points in order to accurately render a bespoke shaped route. This will become important later.
Here it is shown in BaseCamp:
We also know that Lee sees the same anomaly when he looks at it on his PC, so we can be sure it’s not a curious glitch brought about by me using a Mac. That being the case, we can use this section as a simple reference point for what comes next.
I then sent the track and the semi-corrupt route to my fully up-to-date Nav VI, the same device as used by the OP. Not surprisingly the device displayed the track perfectly but displayed the route as straight lines. Just as importantly it showed the route as taking no time at all to travel 128 miles. So, we have straight lines and no time; something is very wrong. The track however looks OK:
I then asked the Nav VI to convert the track into a route. This worked perfectly, including (correctly and accurately) the problem area referred to above:
I am confident that I could have used it and ridden the route without any problems.
Happy with that result, I turned the Nav VI’s attention to the straight line semi-corrupt route. To change straight lines into a route that follows roads, you have to force a recalculation. I did this by changing the mode to car. The device recalculated the route, rendering up something that looked pretty much like the track version. As I have my car preferences on my Nav VI set to match motorcycling, I knew that it would be the same if I sent it back to motorcycling mode. I did it anyway, which forced another recalculation. Again the route looked OK… BUT…. It showed the missing out of the section at the B4016 and the part thereafter. In other words the route went a little way up the B4016 to the shaping point (see above) turned around and came back again, to rejoin the A417, continuing on until the next and nearly last shaping point on the A4155 between Medmenham and Marlow.
We therefore now have a route created from a track that is correct and a route created from a semi-corrupt route, that is wrong.
To check that the route created from the track worked OK, I asked the Nav VI to take me from my house in central London to the start point and then onto the end. This it did, perfectly. I am confident that I could have left my front door, followed the magenta line to the start point and then followed the magenta line of the route (with all its twists and ti]urns and stop off points) for 163 miles to the end.
CONCLUSION
A. The problems all seem to stem from the use of My Route to create the route in the first place. Had the route been created in BaseCamp, none of the problems would have occurred. That much I am confident of.
B. The lack of sufficient shaping points, means that the Nav VI was unable to properly create the correct route from the My Route version. A route created or at least checked in BaseCamp, would have avoided this issue. The creator of the route would have seen the problem and re-shaped the route properly.
C. The Nav VI was not to blame. It did what it could with what it was given to work with. Mix in some possible user error and the end result is all but inevitable.
D. We see this or very similar problems, time after time, on these pages. 99 times out of 100 it is always the same causes.
ADVICE
1. Always check any route (and particularly one that’s come from a third party, like My Route, a magazine or a mate) BEFORE you leave home. Mistakes and errors are easier to sort out at home, than on the roadside.
2. Use BasCamp to at least check the route, rather than just sending it straight to a GPS device.
3. Preferably, cut out using My Route entirely. BaseCamp really isn’t hard.
Richard
PS Moved back into the My Route sub-section.