Zumo XT "Cannot Calculate the Route"

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Peobody
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Re: Zumo XT "Cannot Calculate the Route"

Post by Peobody »

It sounds like your experience with the 660 has you well prepared for the XT.
I, like you, use BC for all of my motorcycle routing. Google maps as always open as well. It really is astounding how different the maps can be.
Grabcon wrote: 29 Aug 2022 01:42 Also one would think that since both Basecamp and the XT and other Satnav units from Garmin would use the same routing algorithms and produce the same results regardless of where they are created.
I wish! It appears that the algorithms in the satnavs keep evolving while Basecamp development has been dead for awhile. I think our challenge will always be in trying to out-think the satnav through the use of shaping points to get it to route where we want to go.
Grabcon wrote: 29 Aug 2022 01:42 If the map data sets are different the results have the potential to be different
Indeed. It remains important to be using the same maps in BC as in the XT.

I have not had the pleasure of riding in your part of the country. I have flown into Scottsdale and done the Flagstaff/Sedona/Canyon tourist stuff by rental car but that's it (at least is was a Camaro convertible). The closest I have come on a bike is Santa Fe.

Ride safe!
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Re: Zumo XT "Cannot Calculate the Route"

Post by jfheath »

An interesting thread .

I've not chipped in any additional comments - I can be of no help with these sorts of issues using USA maps because I can no longer download the USA area that I want from OSM in order to carry out any meaningful tests. I'm based in the Uk. But I do know that the maps in North Carolina can cause some weird behaviour - they seem to have roads plotted that disappeared years ago.

In any case @Peobody is doing a much better job than I would.

I will add some observations where I have had 'Cannot Calculate Route'
  • Route points plotted slightly off route
  • Route points plotted on wrong side of dual carriageway.
  • Route points placed in a position which makes the calculation of a sensible route difficult eg when the sequence is wrong.
  • Selecting Closest Entry Point (sometimes) when you are already on the route
  • Selecting CEP before the route has started or when the position of the bike means that CEP could not draw a straight line at right angles to any point on the route
  • Deviating from the route that has been calculated to reach the CEP.
  • Repeatedly ignoring instructions to U turn having decided to take a better route from the one plotted.

One clarification worth making:
Peobody wrote: 29 Aug 2022 01:18 Hint: skipping a point will cause the XT to recalc to the end of the route not just to the next point.
That is correct - Pressing the skip button does indeed cause the entire route to be recalculated from your present position. It will leave out the point to skip, but the recalculated route will still visit all of the remaining route point in the correct order. I know that this is what Peobody meant, but there is a common situation when the XT will calculate to the end of the route and ignore all of the intermediate route points, so the distinction is worth mentioning.
(ie - when starting a route selecting the wrong 'destination'; when editing a trip converted from a track)
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Re: Zumo XT "Cannot Calculate the Route"

Post by Grabcon »

jfheath wrote: 05 Sep 2022 06:52 But I do know that the maps in North Carolina can cause some weird behaviour - they seem to have roads plotted that disappeared years ago.

[/i]
This is common in the USA. I believe that it has to do with how the map database was created and how it is maintained. This could be a long and complicated discussion/explanation so I will try to keep it simple.

I am going to take a SWAG here and say that the original map database was and is potentially built/maintained by a collection/compilation of thousands of map databases in the US. These most likely have come from the county level in each state. The US to the best of my knowledge does not have a standardized road network database covering every state at all levels of road classifications.

Many if not all of these county level databases were created in the early years of digital mapping and have been maintained over the years using a multitude of methods. Many secondary, urban, country roads etc. may or may not exist in reality. This is dependent on how the data was entered and maintained. Many roads get added from land developer surveys and if the land development project takes many years the road in reality may not exist but does exist in the map database. I know for a fact where I am at in Arizona that there are many roads that are shown even in Google maps that do not exist, but the routing in Google will still try to using them. It is very annoying. Higher level roads Interstate, state, county level roads are well maintained.

I am going to venture a guess and say that there is a priority level set as to the order of what roads get up dated in the map database based on the road type. Who does these updates is still very unclear since there are several sources of data for maps across the county and all are similar but could be different at some level of detail. As an example in basecamp and Google I have found many times that there are different names for the same road. This typically happens at the lower level of the road priority, urban streets, non-county country roads and dirt roads.

I typically use two sources of map data when creating routes in Basecamp for use in my SatNav units. This is where I will find discrepancies in map data and maybe have to use Google Earth for a better view of road surface and such.

From my experience if I cannot see a road track with satellite imagery is on in Google/google earth the road either don't exist or it is very under used and does not show well in the imagery. Typically these would be roads that are dirt/two track.

It is still baffling as to how of this data is maintained, especially at a global level. If one is to look at the number of the road segments in the map databases that are added and maintained on a regular basis it is astounding how good the data is. There are millions of road segments that are in these databases and all of the underlying attributes that are required to do what we want these systems to do. And then there are all of the other data components that are maintained all POI's, address data, directional data, etc. If we are looking at error rates for every million data elements with a .01% error rate that is a 1000 errors in data elements per million elements. How is this level of accuracy maintained on a continuous level. As a qualifier I am just using .01% as a guessed level of accuracy because I don't really know. But still as users we will most likely not see many of these errors as they are not available for our visualization but are used by the routing algorithms.

I don't think as users we understand the complexity of what goes in to what our mapping and navigation systems go thru to make them usable for us as users.
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Re: Zumo XT "Cannot Calculate the Route"

Post by Peobody »

I agree with this synopsys and also do my routing in Basecamp in conjunction with Google maps, its satellite view, and its street view where available. Here in North Carolina I have encountered gravel roads shown as paved, paved roads shown as gravel, terrible placement of POI's, even an interstate exit that didn't exists (research after the fact found that it had been removed 3 years previously). I can't imagine what the communication between the map makers and the numerous agencies responsible for roads looks like but I'm sure it's a mess. Still, our frustration is understandable considering how much more accurate Google maps is, although it can be annoying when things show up on Google maps that haven't been built yet.
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Re: Zumo XT "Cannot Calculate the Route"

Post by Grabcon »

When I was in the Geographic Information System "GIS" industry or digital cartography there were three things that I used as a measure for information accuracy. It was what I called "QIC" Quality, Integrity & Completeness. Each of which describe different aspects of data management but all which drive accuracy and precision of the data and make the data usable for what ever the specific needs maybe. This mapping process is a very complex issue more so than what I think users understand. Then like you mention there is data latency, what exists and what doesn't and when that happened.