refactor merging of segregated roads

adjust to generalFindMaximum function
moved parallel detection to ratio/absolute based regression testing
considerably improved detection quality using normalised regression lines
only follow initial direction/narrow turns for parallel detection

src/extractor/guidance/intersection_handler.cpp

@@ -5,10 +5,14 @@
 #include "util/guidance/name_announcements.hpp"
 #include "util/log.hpp"
 
+#include "util/bearing.hpp"
+#include "util/coordinate_calculation.hpp"
+
 #include <algorithm>
 #include <cstddef>
 
 using EdgeData = osrm::util::NodeBasedDynamicGraph::EdgeData;
+using osrm::extractor::guidance::getTurnDirection;
 using osrm::util::angularDeviation;
 
 namespace osrm
@@ -384,19 +388,17 @@ IntersectionHandler::getNextIntersection(const NodeID at, const EdgeID via) cons
     // Starting at node `a` via edge `e0` the intersection generator returns the intersection at `c`
     // writing `tl` (traffic signal) node and the edge `e1` which has the intersection as target.
 
-    NodeID node = SPECIAL_NODEID;
-    EdgeID edge = SPECIAL_EDGEID;
-
-    std::tie(node, edge) = intersection_generator.SkipDegreeTwoNodes(at, via);
-    auto intersection = intersection_generator(node, edge);
-
+    const auto intersection_parameters = intersection_generator.SkipDegreeTwoNodes(at, via);
     // This should never happen, guard against nevertheless
-    if (node == SPECIAL_NODEID || edge == SPECIAL_EDGEID)
+    if (intersection_parameters.nid == SPECIAL_NODEID ||
+        intersection_parameters.via_eid == SPECIAL_EDGEID)
     {
         return boost::none;
     }
 
-    auto intersection_node = node_based_graph.GetTarget(edge);
+    auto intersection =
+        intersection_generator(intersection_parameters.nid, intersection_parameters.via_eid);
+    auto intersection_node = node_based_graph.GetTarget(intersection_parameters.via_eid);
 
     if (intersection.size() <= 2 || intersection.isTrafficSignalOrBarrier())
     {