handle combined turns at segregated roads

include/engine/api/route_api.hpp

@@ -132,6 +132,7 @@ class RouteAPI : public BaseAPI
 
                 guidance::trimShortSegments(steps, leg_geometry);
                 leg.steps = guidance::postProcess(std::move(steps));
+                leg.steps = guidance::collapseTurns(std::move(leg.steps));
                 leg.steps = guidance::assignRelativeLocations(std::move(leg.steps), leg_geometry,
                                                               phantoms.source_phantom,
                                                               phantoms.target_phantom);

include/engine/guidance/post_processing.hpp

@@ -17,6 +17,13 @@ namespace guidance
 // passed as none-reference to modify in-place and move out again
 std::vector<RouteStep> postProcess(std::vector<RouteStep> steps);
 
+// Multiple possible reasons can result in unnecessary/confusing instructions
+// A prime example would be a segregated intersection. Turning around at this
+// intersection would result in two instructions to turn left.
+// Collapsing such turns into a single turn instruction, we give a clearer
+// set of instructionst that is not cluttered by unnecessary turns/name changes.
+std::vector<RouteStep> collapseTurns(std::vector<RouteStep> steps);
+
 // trim initial/final segment of very short length.
 // This function uses in/out parameter passing to modify both steps and geometry in place.
 // We use this method since both steps and geometry are closely coupled logically but
@@ -30,6 +37,9 @@ std::vector<RouteStep> assignRelativeLocations(std::vector<RouteStep> steps,
                                                const PhantomNode &source_node,
                                                const PhantomNode &target_node);
 
+//remove steps invalidated by post-processing
+std::vector<RouteStep> removeNoTurnInstructions(std::vector<RouteStep> steps);
+
 // postProcess will break the connection between the leg geometry
 // for which a segment is supposed to represent exactly the coordinates
 // between routing maneuvers and the route steps itself.

include/engine/guidance/toolkit.hpp

@@ -4,6 +4,8 @@
 #include "extractor/guidance/turn_instruction.hpp"
 #include "util/bearing.hpp"
 
+#include <algorithm>
+
 namespace osrm
 {
 namespace engine
@@ -56,6 +58,12 @@ inline extractor::guidance::DirectionModifier angleToDirectionModifier(const dou
     return extractor::guidance::DirectionModifier::Left;
 }
 
+inline double angularDeviation(const double angle, const double from)
+{
+        const double deviation = std::abs(angle - from);
+            return std::min(360 - deviation, deviation);
+}
+
 } // namespace guidance
 } // namespace engine
 } // namespace osrm