Strange loops while importing
Reasons for Strange Loops
There can be 4 reasons for strange loops during route import and creation (the first 2 only apply to import):
1. Converting a coordinate list to a navigable route.
To convert a list of (sometimes thousands) coordinates into a navigable route is difficult. You can’t feed thousands of coordinates to a route calculation as that would cause performance problems, so you need to reduce the coordinates in a ‘smart’ way, leaving only key coordinates for the route to be calculated correctly. Unfortunately this can never be made to work 100% correct for all routes as routes vary a lot in distance and complexity of the underlying road network (urban route vs country-side route for example). That is why Scenic allows to manually adjust the via points in the route during importing. If you’d like to know more details you can read this blog article.
2. Difference in ‘road snapping’ between the route source and Scenic.
Scenic uses a 3rd party map provider which bases their maps on Open Street Maps (OSM), but there are many other map providers out there. Most commonly used are Google Maps, Garmin, TomTom and OSM. Although most roads are the same on all these maps, the route calculation (incl. road snapping) can be quite different. As an example, it could happen that a coordinate is passed to Scenic which, the source map deems to be on (or snaps to) one side of a road, while Scenic (OSM) might interpret (or snap) that coordinate to being on the other (sometimes separated) side of the road, or even, if the coordinate is very close to an intersection, on another road. This can cause the calculated route to be different or even send you back and forth, because Scenic wants you to go along the roads (and sometimes road sides) it snapped the coordinates to. Take this conceptual situation for example:
In this example point 2 is snapped to the wrong side and you see what happens. To get from point 1 to 2, it sends you to the first possibility to turn around and guides to point 2. Then it wants you to reach point 3 and turns you around again on the first possibility. A strange loop is the result.
3. Via point placement is very sensitive.
Scenic is very sensitive to the location where via points are placed. Even which side of the road you place a via point can be important. If you place a via on (or it is snapped to) the ‘wrong’ side of the road loops can be created because Scenic does not want you to go against traffic, so it sends you in a loop to reach the via point from the other side.
4. Incorrect or incomplete map data
OSM are maps based on satellite data enriched with maintenance by an open community of about 2 million users worldwide. Some areas have a very active community, while others are not that active. So, it can happen that roads and road data (like avg speed, speed limits, names, etc.) are incomplete or incorrect. This depends partially on how active the community in your region is.
How to correct Strange Loops
Loops caused by the first 3 reasons can mostly be removed by removing/moving or adding via points. (Take a look at the detailed tutorial video on how to do this). Loops resulting from the last reason can only be handled by a workaround. If it’s a ferry crossing have a look here. If it’s not a ferry crossing, have a look here on how to deal with this.