Roundabout Intersections are roundabouts with up to four ways and turn
angles which makes the turns obvious, e.g. as in:
```
*
*
* * * *
*
*
```
but not
```
*
*
* * *
* *
* *
```
For Roundabout Intersections we issue instructions such as
"turn <direction>" instead of "take the <nth> exit".
At the moment we have a limit on the radius for these Roundabout
Intersections of 5 meters. Which fails to classify a wide range of
Roundabout Intersections in the US (with the US-wide streets).
This changeset removes the Roundabout Intersection radius limit:
- if the roundabout is larger than a threshold and is named we classify
it as a rotary
- if the roundabout matches our criteria for Roundabout Intersections
we classify it as a Roundabout Intersection
- else fallback to plain old Roundabout
There is a second issue with determining a roundabout's radius.
But that's for another pull request (tracking in #2716).
References:
- https://github.com/Project-OSRM/osrm-backend/issues/2716
Staggered intersection are very short zig-zags of only a few meters.
They are common in rural and exurban areas, especially in the US.
(In addition, these cases could as well be tagging issues)
We do not want to announce these short left-rights or right-lefts:
* -> b a -> *
| or | becomes a -> b
a -> * * -> b
Here is one example:
- https://www.openstreetmap.org/edit#map=20/39.26017/-84.25182
And here are two edge-cases that we don't handle at the moment:
- http://www.openstreetmap.org/edit#map=20/38.87900/-76.98519
- http://www.openstreetmap.org/edit#map=19/45.51056/-122.63462
and probably should not handle since the distance in between is
quite long (roughly 7-15 meters). For these we want to announce
two turns to not confuse the user.
Thanks to @1ec5 for raising this issue and @karenzshea for
providing additional US examples and cultural insights.
https://github.com/Project-OSRM/osrm-backend/pull/2685/files
fixes an issue where we did
elongate(fstStep, sndStep);
instead of
newStep = elongate(fstStep, sndStep);
we didn't get any warnings.
The only way to trigger a warning here is to use
```cpp
__attribute__((warn_unused_result))
```
This changeset does exactly that: for the new guidance code prone to
these kind of issue we add such an attribute to the declaration.
