Rember Intersection Shapes

Changes the processing order in the edge based graph factory.
Instead of iterating over all outgoing edges in order, we compute the edge
expanded graph in the order of intersections.
This allows to remember intersection shapes and re-use them for all possible ingoing edges.

Also: use low accuracry mode for intersections degree 2 intersections

We can use lower accuracy here, since the `bearing`
after the turn is not as relevant for off-route detection.
Getting lost is near impossible here.

include/util/bearing.hpp

@@ -8,9 +8,9 @@ namespace osrm
 {
 namespace util
 {
-
 namespace bearing
 {
+
 inline std::string get(const double heading)
 {
     BOOST_ASSERT(heading >= 0);
@@ -96,8 +96,40 @@ inline double reverseBearing(const double bearing)
         return bearing - 180.;
     return bearing + 180;
 }
-}
-}
+
+// Compute the angle between two bearings on a normal turn circle
+//
+//      Bearings                      Angles
+//
+//         0                           180
+//   315         45               225       135
+//
+// 270     x       90           270     x      90
+//
+//   225        135               315        45
+//        180                           0
+//
+// A turn from north to north-east offerst bearing 0 and 45 has to be translated
+// into a turn of 135 degrees. The same holdes for 90 - 135 (east to south
+// east).
+// For north, the transformation works by angle = 540 (360 + 180) - exit_bearing
+// % 360;
+// All other cases are handled by first rotating both bearings to an
+// entry_bearing of 0.
+inline double angleBetweenBearings(const double entry_bearing, const double exit_bearing)
+{
+    const double offset = 360 - entry_bearing;
+    const double rotated_exit = [](double bearing, const double offset) {
+        bearing += offset;
+        return bearing > 360 ? bearing - 360 : bearing;
+    }(exit_bearing, offset);
+
+    const auto angle = 540 - rotated_exit;
+    return angle >= 360 ? angle - 360 : angle;
 }
 
+} // namespace bearing
+} // namespace util
+} // namespace osrm
+
 #endif // BEARING_HPP