Same route. Some waypoints set to Vias. Some waypoints set to Shaping. Lots of additional adhoc points all set to Shaping.
Route had previously been recalculated and I know what to look for when it does. Two locations in particular are significant changes. I describe these below
Three tests carried out.
Phone with link to Explore database is turned off. XT2 cannot synch in this state.
1a. Check route after placing it onto the SD card and Importing it to the XT2. Do not load.
1b. Route imported. Current.gpx copied and checked. No changes on XT2 map. No changes to Current.gpx.
1b - Selected Go ! on route and then skipped start point. I could only find one change in the route - a very minor one. Took a copy of Current.gpx
Before test 1c, I stopped the test from 1b, deleted the route and reloaded the original. The route had not been altered.
1c. I imported the Test route again. So everything is as it was for test 2. Turned on the phone, established the link between Tread and the Zumo XT2. And saw that the XT2 had synch'd at 11:54 and again at 11:55. Closed down the XT2 and took a copy of Current.gpx
I stripped out all of the tags from the three current.gpx files. so that only the lat, long and name of the route points remained - separated by commas. (this is quite easy to do in Word with it Macro facilites and very sophisticated find and replace). Then imported the CSV files into an excel spreadsheet and got Excel to compare tests 1b with 1a and 1c with 1a. (1a is the original route)
- Test1 Comparing results from 1a 1b and 1c.png (636.45 KiB) Viewed 501 times
1a is identical to 1b (I gave the lat/long values a bit of leeway of 0.00001) Names are unchanged, locations are unchanged. Route appeared to be unchanded on the maps.
1c is different. The green background represents the Via Points. These were all created as Waypoints, but two other points were created as Waypoints as well, but these were set as Shaping Points and they have changed as well. Every single shaping point has been moved and renamed.
Largely, these shaping points remained on the original route (but there are not man alternatives). Two important ones did not, and it altered the route - not significantly, but in a way that I did not want it to be altered. It seems that between Via Points, the system calculates a route close to the original, but improves it using its own preferences. And then puts in the same number of shaping points to keep the new route in place - but in completely new locations.
I've asked Excel to indicate with **** data that has been changed from T1a. and with Ok if it hasn't.
I think that this reproduces what @smfollen discovered in his tests. Just allowing the route to synch with the Explore database changes the route. I could not establish whether it did it after sending the data to the Explore database, or if it did it when it re-synched. That second statement should not happen surely - you don't expect your route to be sent, marked, corrected and then sent back. Whatever. it didn't happen before I turned on Tread.
But can I still use Tread to communicate - eg other, road works, road closures etc without having it Sync to Tread. I suppose I have to destroy the connection by resetting the explore database - so that it doesn't know how to connect me to it. Thats how I kept my XT2 for a while before I ventured into using Tread. These results suggest that the route behaves impeccably.
I think that this suggests that any gpx file from anywhere is going to suffer the same fate. I'd need to check that out.
--------------------------------
The significant alterations.
- Test 1 Relocated Shaping Points.png (360.21 KiB) Viewed 503 times
In both cases the route that I had planned follows the grey track. In the left hand picture I am heading North. The first shaping point in the bottom left is OK - I want to take that road. When that road meets the A685, I want to turn right. I had a shaping point in the area of the red circle, to force the route to take that road. There is a reason for this. I was leading a group of 10 motorcycles. If I turn left and then right onto the A6 then I am faced with a very busy right hand turn which is just after a a bend. To get 8 motorcycles out of that junction without gettting spread out by about 10 minutes is almost impossible. So I turn right and then head for the A6 on a much quieter junction - where traffic is helf up by frequently changing traffic lights.
The left hand picture shows a similar situation. I marked the road that I wanted to take with two shaping points - where the red circles are. The satnav deleted them and repalced them with two shaping points on the route that it preferred. A very narrow country lane with no way that a motorcycle can pass a car coming in the opposite directions, and often full of road debris / puncture risk .
