improve sliproad / fork handling

features/guidance/dedicated-turn-roads.feature

@@ -167,3 +167,34 @@ Feature: Slipways and Dedicated Turn Lanes
         When I route I should get
             | waypoints | route                                                     | turns                    |
             | a,o       | Schwarzwaldstrasse (L561),Ettlinger Allee,Ettlinger Allee | depart,turn right,arrive |
+
+    Scenario: Traffic Lights everywhere
+        #http://map.project-osrm.org/?z=18&center=48.995336%2C8.383813&loc=48.995467%2C8.384548&loc=48.995115%2C8.382761&hl=en&alt=0
+        Given the node map
+            | a |   |   | k | l |   |   | j |   |
+            |   |   |   |   |   | d | b | c | i |
+            |   |   |   |   |   |   |   |   |   |
+            |   |   |   |   |   |   | e | g |   |
+            |   |   |   |   |   |   |   |   |   |
+            |   |   |   |   |   |   |   |   |   |
+            |   |   |   |   |   |   |   | h |   |
+            |   |   |   |   |   |   |   |   |   |
+            |   |   |   |   |   |   |   | f |   |
+
+        And the nodes
+            | node | highway         |
+            | b    | traffic_signals |
+            | e    | traffic_signals |
+            | g    | traffic_signals |
+
+        And the ways
+            | nodes  | highway        | name          | oneway |
+            | aklbci | secondary      | Ebertstrasse  | yes    |
+            | kdeh   | secondary_link |               | yes    |
+            | jcghf  | primary        | Brauerstrasse | yes    |
+
+        When I route I should get
+            | waypoints | route                                    | turns                    |
+            | a,i       | Ebertstrasse,Ebertstrasse                | depart,arrive            |
+            | a,l       | Ebertstrasse,Ebertstrasse                | depart,arrive            |
+            | a,f       | Ebertstrasse,Brauerstrasse,Brauerstrasse | depart,turn right,arrive |

include/extractor/guidance/intersection_handler.hpp

@@ -29,7 +29,8 @@ class IntersectionHandler
                         const std::vector<QueryNode> &node_info_list,
                         const util::NameTable &name_table,
                         const SuffixTable &street_name_suffix_table);
-    virtual ~IntersectionHandler();
+
+    virtual ~IntersectionHandler() = default;
 
     // check whether the handler can actually handle the intersection
     virtual bool
@@ -51,6 +52,9 @@ class IntersectionHandler
     // Decide on a basic turn types
     TurnType::Enum findBasicTurnType(const EdgeID via_edge, const ConnectedRoad &candidate) const;
 
+    // Find the most obvious turn to follow
+    std::size_t findObviousTurn(const EdgeID via_edge, const Intersection &intersection) const;
+
     // Get the Instruction for an obvious turn
     TurnInstruction getInstructionForObvious(const std::size_t number_of_candidates,
                                              const EdgeID via_edge,

include/extractor/guidance/intersection_scenario_three_way.hpp

@@ -10,11 +10,6 @@ namespace extractor
 namespace guidance
 {
 
-// possible fork
-bool isFork(const ConnectedRoad &uturn,
-            const ConnectedRoad &possible_right_fork,
-            const ConnectedRoad &possible_left_fork);
-
 // Ending in a T-Intersection
 bool isEndOfRoad(const ConnectedRoad &uturn,
                  const ConnectedRoad &possible_right_turn,

include/extractor/guidance/motorway_handler.hpp

@@ -26,7 +26,8 @@ class MotorwayHandler : public IntersectionHandler
                     const std::vector<QueryNode> &node_info_list,
                     const util::NameTable &name_table,
                     const SuffixTable &street_name_suffix_table);
-    ~MotorwayHandler() override final;
+
+    ~MotorwayHandler() override final = default;
 
     // check whether the handler can actually handle the intersection
     bool canProcess(const NodeID nid,

include/extractor/guidance/roundabout_handler.hpp

@@ -44,7 +44,7 @@ class RoundaboutHandler : public IntersectionHandler
                       const util::NameTable &name_table,
                       const SuffixTable &street_name_suffix_table);
 
-    ~RoundaboutHandler() override final;
+    ~RoundaboutHandler() override final = default;
 
     // check whether the handler can actually handle the intersection
     bool canProcess(const NodeID from_nid,

include/extractor/guidance/sliproad_handler.hpp

@@ -0,0 +1,53 @@
+#ifndef OSRM_EXTRACTOR_GUIDANCE_SLIPROAD_HANDLER_HPP_
+#define OSRM_EXTRACTOR_GUIDANCE_SLIPROAD_HANDLER_HPP_
+
+#include "extractor/guidance/intersection.hpp"
+#include "extractor/guidance/intersection_handler.hpp"
+#include "extractor/guidance/intersection_generator.hpp"
+#include "extractor/query_node.hpp"
+
+#include "util/name_table.hpp"
+#include "util/node_based_graph.hpp"
+
+#include <cstddef>
+#include <utility>
+#include <vector>
+
+namespace osrm
+{
+namespace extractor
+{
+namespace guidance
+{
+
+// Intersection handlers deal with all issues related to intersections.
+// They assign appropriate turn operations to the TurnOperations.
+class SliproadHandler : public IntersectionHandler
+{
+  public:
+    SliproadHandler(const IntersectionGenerator &intersection_generator,
+                    const util::NodeBasedDynamicGraph &node_based_graph,
+                    const std::vector<QueryNode> &node_info_list,
+                    const util::NameTable &name_table,
+                    const SuffixTable &street_name_suffix_table);
+
+    ~SliproadHandler() override final = default;
+
+    // check whether the handler can actually handle the intersection
+    bool canProcess(const NodeID /*nid*/,
+                    const EdgeID /*via_eid*/,
+                    const Intersection & /*intersection*/) const override final;
+
+    // process the intersection
+    Intersection operator()(const NodeID nid,
+                            const EdgeID via_eid,
+                            Intersection intersection) const override final;
+  private:
+    const IntersectionGenerator &intersection_generator;
+};
+
+} // namespace guidance
+} // namespace extractor
+} // namespace osrm
+
+#endif /*OSRM_EXTRACTOR_GUIDANCE_SLIPROAD_HANDLER_HPP_*/

include/extractor/guidance/toolkit.hpp

@@ -428,7 +428,7 @@ inline int getPriority(const FunctionalRoadClass road_class)
     // They are used in Fork-Discovery. Possibly should be moved to profiles post v5?
     // A fork can happen between road types that are at most 1 priority apart from each other
     const constexpr int road_priority[] = {
-        10, 0, 10, 2, 10, 4, 10, 6, 10, 8, 10, 11, 10, 12, 10, 14};
+        14, 0, 14, 2, 14, 4, 14, 6, 14, 8, 10, 11, 10, 12, 10, 14};
     return road_priority[static_cast<int>(road_class)];
 }
 

include/extractor/guidance/turn_analysis.hpp

@@ -6,6 +6,7 @@
 #include "extractor/guidance/intersection_generator.hpp"
 #include "extractor/guidance/motorway_handler.hpp"
 #include "extractor/guidance/roundabout_handler.hpp"
+#include "extractor/guidance/sliproad_handler.hpp"
 #include "extractor/guidance/toolkit.hpp"
 #include "extractor/guidance/turn_classification.hpp"
 #include "extractor/guidance/turn_handler.hpp"
@@ -59,13 +60,11 @@ class TurnAnalysis
     const RoundaboutHandler roundabout_handler;
     const MotorwayHandler motorway_handler;
     const TurnHandler turn_handler;
+    const SliproadHandler sliproad_handler;
 
     // Utility function, setting basic turn types. Prepares for normal turn handling.
     Intersection
     setTurnTypes(const NodeID from, const EdgeID via_edge, Intersection intersection) const;
-
-    Intersection handleSliproads(const NodeID intersection_node_id,
-                                 Intersection intersection) const;
 }; // class TurnAnalysis
 
 } // namespace guidance

include/extractor/guidance/turn_handler.hpp

@@ -28,7 +28,8 @@ class TurnHandler : public IntersectionHandler
                 const std::vector<QueryNode> &node_info_list,
                 const util::NameTable &name_table,
                 const SuffixTable &street_name_suffix_table);
-    ~TurnHandler() override final;
+
+    ~TurnHandler() override final = default;
 
     // check whether the handler can actually handle the intersection
     bool canProcess(const NodeID nid,
@@ -41,6 +42,9 @@ class TurnHandler : public IntersectionHandler
                             Intersection intersection) const override final;
 
   private:
+    bool isObviousOfTwo(const EdgeID via_edge,
+                        const ConnectedRoad &road,
+                        const ConnectedRoad &other) const;
     // Dead end.
     Intersection handleOneWayTurn(Intersection intersection) const;
 
@@ -57,8 +61,7 @@ class TurnHandler : public IntersectionHandler
     handleDistinctConflict(const EdgeID via_edge, ConnectedRoad &left, ConnectedRoad &right) const;
 
     // Classification
-    std::size_t findObviousTurn(const EdgeID via_edge, const Intersection &intersection) const;
-    std::pair<std::size_t, std::size_t> findFork(const Intersection &intersection) const;
+    std::pair<std::size_t, std::size_t> findFork(const EdgeID via_edge, const Intersection &intersection) const;
 
     Intersection assignLeftTurns(const EdgeID via_edge,
                                  Intersection intersection,

src/engine/guidance/post_processing.cpp

@@ -719,6 +719,16 @@ std::vector<RouteStep> collapseTurns(std::vector<RouteStep> steps)
         // Handle sliproads from motorways in urban areas, save from modifying depart, since
         // TurnType::Sliproad != TurnType::NoTurn
         if (one_back_step.maneuver.instruction.type == TurnType::Sliproad)
+        {
+            if (current_step.maneuver.instruction.type == TurnType::Suppressed &&
+                compatible(one_back_step, current_step))
+            {
+                // Traffic light on the sliproad
+                steps[one_back_index] =
+                    elongate(std::move(steps[one_back_index]), steps[step_index]);
+                invalidateStep(steps[step_index]);
+            }
+            else
             {
                 // Handle possible u-turns between highways that look like slip-roads
                 if (steps[getPreviousIndex(one_back_index)].name_id == steps[step_index].name_id &&
@@ -750,6 +760,7 @@ std::vector<RouteStep> collapseTurns(std::vector<RouteStep> steps)
                     invalidateStep(steps[step_index]);
                 }
             }
+        }
         // Due to empty segments, we can get name-changes from A->A
         // These have to be handled in post-processing
         else if (isCollapsableInstruction(current_step.maneuver.instruction) &&

src/extractor/guidance/intersection_handler.cpp

@@ -1,5 +1,5 @@
-#include "extractor/guidance/intersection_handler.hpp"
 #include "extractor/guidance/constants.hpp"
+#include "extractor/guidance/intersection_handler.hpp"
 #include "extractor/guidance/toolkit.hpp"
 
 #include "util/guidance/toolkit.hpp"
@@ -34,8 +34,6 @@ IntersectionHandler::IntersectionHandler(const util::NodeBasedDynamicGraph &node
 {
 }
 
-IntersectionHandler::~IntersectionHandler() = default;
-
 std::size_t IntersectionHandler::countValid(const Intersection &intersection) const
 {
     return std::count_if(intersection.begin(), intersection.end(), [](const ConnectedRoad &road) {
@@ -322,6 +320,115 @@ bool IntersectionHandler::isThroughStreet(const std::size_t index,
     return false;
 }
 
+std::size_t IntersectionHandler::findObviousTurn(const EdgeID via_edge,
+                                                 const Intersection &intersection) const
+{
+    // no obvious road
+    if (intersection.size() == 1)
+        return 0;
+
+    // a single non u-turn is obvious
+    if (intersection.size() == 2)
+        return 1;
+
+    // at least three roads
+    std::size_t best = 0;
+    double best_deviation = 180;
+
+    std::size_t best_continue = 0;
+    double best_continue_deviation = 180;
+
+    const EdgeData &in_data = node_based_graph.GetEdgeData(via_edge);
+    for (std::size_t i = 1; i < intersection.size(); ++i)
+    {
+        const double deviation = angularDeviation(intersection[i].turn.angle, STRAIGHT_ANGLE);
+        if (intersection[i].entry_allowed && deviation < best_deviation)
+        {
+            best_deviation = deviation;
+            best = i;
+        }
+
+        const auto out_data = node_based_graph.GetEdgeData(intersection[i].turn.eid);
+        auto continue_class = node_based_graph.GetEdgeData(intersection[best_continue].turn.eid)
+                                  .road_classification.road_class;
+        if (intersection[i].entry_allowed && out_data.name_id == in_data.name_id &&
+            (best_continue == 0 || continue_class > out_data.road_classification.road_class ||
+             (deviation < best_continue_deviation &&
+              out_data.road_classification.road_class == continue_class)))
+        {
+            best_continue_deviation = deviation;
+            best_continue = i;
+        }
+    }
+
+    if (best == 0)
+        return 0;
+
+    if (best_deviation >= 2 * NARROW_TURN_ANGLE)
+        return 0;
+    // has no obvious continued road
+    if (best_continue == 0 || best_continue_deviation >= 2 * NARROW_TURN_ANGLE ||
+        (node_based_graph.GetEdgeData(intersection[best_continue].turn.eid)
+                 .road_classification.road_class ==
+             node_based_graph.GetEdgeData(intersection[best].turn.eid)
+                 .road_classification.road_class &&
+         std::abs(best_continue_deviation) > 1 && best_deviation / best_continue_deviation < 0.75))
+    {
+        // Find left/right deviation
+        const double left_deviation = angularDeviation(
+            intersection[(best + 1) % intersection.size()].turn.angle, STRAIGHT_ANGLE);
+        const double right_deviation =
+            angularDeviation(intersection[best - 1].turn.angle, STRAIGHT_ANGLE);
+
+        if (best_deviation < MAXIMAL_ALLOWED_NO_TURN_DEVIATION &&
+            std::min(left_deviation, right_deviation) > FUZZY_ANGLE_DIFFERENCE)
+            return best;
+
+        // other narrow turns?
+        if (angularDeviation(intersection[best - 1].turn.angle, STRAIGHT_ANGLE) <=
+            FUZZY_ANGLE_DIFFERENCE)
+            return 0;
+        if (angularDeviation(intersection[(best + 1) % intersection.size()].turn.angle,
+                             STRAIGHT_ANGLE) <= FUZZY_ANGLE_DIFFERENCE)
+            return 0;
+
+        // Well distinct turn that is nearly straight
+        if ((left_deviation / best_deviation >= DISTINCTION_RATIO ||
+             (left_deviation > best_deviation &&
+              !intersection[(best + 1) % intersection.size()].entry_allowed)) &&
+            (right_deviation / best_deviation >= DISTINCTION_RATIO ||
+             (right_deviation > best_deviation && !intersection[best - 1].entry_allowed)))
+        {
+            return best;
+        }
+    }
+    else
+    {
+        const double deviation =
+            angularDeviation(intersection[best_continue].turn.angle, STRAIGHT_ANGLE);
+        const auto &continue_data =
+            node_based_graph.GetEdgeData(intersection[best_continue].turn.eid);
+        if (std::abs(deviation) < 1)
+            return best_continue;
+
+        // check if any other similar best continues exist
+        for (std::size_t i = 1; i < intersection.size(); ++i)
+        {
+            if (i == best_continue || !intersection[i].entry_allowed)
+                continue;
+
+            if (angularDeviation(intersection[i].turn.angle, STRAIGHT_ANGLE) / deviation < 1.1 &&
+                continue_data.road_classification.road_class ==
+                    node_based_graph.GetEdgeData(intersection[i].turn.eid)
+                        .road_classification.road_class)
+                return 0;
+        }
+        return best_continue; // no obvious turn
+    }
+
+    return 0;
+}
+
 } // namespace guidance
 } // namespace extractor
 } // namespace osrm

src/extractor/guidance/intersection_scenario_three_way.cpp

@@ -13,14 +13,6 @@ namespace extractor
 namespace guidance
 {
 
-bool isFork(const ConnectedRoad &,
-            const ConnectedRoad &possible_right_fork,
-            const ConnectedRoad &possible_left_fork)
-{
-    return angularDeviation(possible_right_fork.turn.angle, STRAIGHT_ANGLE) < NARROW_TURN_ANGLE &&
-           angularDeviation(possible_left_fork.turn.angle, STRAIGHT_ANGLE) < NARROW_TURN_ANGLE;
-}
-
 bool isEndOfRoad(const ConnectedRoad &,
                  const ConnectedRoad &possible_right_turn,
                  const ConnectedRoad &possible_left_turn)

src/extractor/guidance/motorway_handler.cpp

@@ -47,8 +47,6 @@ MotorwayHandler::MotorwayHandler(const util::NodeBasedDynamicGraph &node_based_g
 {
 }
 
-MotorwayHandler::~MotorwayHandler() = default;
-
 bool MotorwayHandler::canProcess(const NodeID,
                                  const EdgeID via_eid,
                                  const Intersection &intersection) const

src/extractor/guidance/roundabout_handler.cpp

@@ -31,8 +31,6 @@ RoundaboutHandler::RoundaboutHandler(const util::NodeBasedDynamicGraph &node_bas
 {
 }
 
-RoundaboutHandler::~RoundaboutHandler() = default;
-
 bool RoundaboutHandler::canProcess(const NodeID from_nid,
                                    const EdgeID via_eid,
                                    const Intersection &intersection) const

src/extractor/guidance/sliproad_handler.cpp

@@ -0,0 +1,192 @@
+#include "extractor/guidance/constants.hpp"
+#include "extractor/guidance/intersection_scenario_three_way.hpp"
+#include "extractor/guidance/sliproad_handler.hpp"
+#include "extractor/guidance/toolkit.hpp"
+
+#include "util/guidance/toolkit.hpp"
+
+#include <limits>
+#include <utility>
+
+#include <boost/assert.hpp>
+
+using EdgeData = osrm::util::NodeBasedDynamicGraph::EdgeData;
+using osrm::util::guidance::getTurnDirection;
+using osrm::util::guidance::angularDeviation;
+
+namespace osrm
+{
+namespace extractor
+{
+namespace guidance
+{
+
+SliproadHandler::SliproadHandler(const IntersectionGenerator &intersection_generator,
+                                 const util::NodeBasedDynamicGraph &node_based_graph,
+                                 const std::vector<QueryNode> &node_info_list,
+                                 const util::NameTable &name_table,
+                                 const SuffixTable &street_name_suffix_table)
+    : IntersectionHandler(node_based_graph, node_info_list, name_table, street_name_suffix_table),
+      intersection_generator(intersection_generator)
+{
+}
+
+// included for interface reasons only
+bool SliproadHandler::canProcess(const NodeID /*nid*/,
+                                 const EdgeID /*via_eid*/,
+                                 const Intersection & /*intersection*/) const
+{
+    return true;
+}
+
+Intersection SliproadHandler::
+operator()(const NodeID, const EdgeID source_edge_id, Intersection intersection) const
+{
+    auto intersection_node_id = node_based_graph.GetTarget(source_edge_id);
+
+    // if there is no turn, there is no sliproad
+    if (intersection.size() <= 2)
+        return intersection;
+
+    const auto obvious_turn_index = findObviousTurn(source_edge_id, intersection);
+    const auto &next_road = intersection[obvious_turn_index];
+
+    const auto linkTest = [this, next_road](const ConnectedRoad &road) {
+        return !node_based_graph.GetEdgeData(road.turn.eid).roundabout && road.entry_allowed &&
+               angularDeviation(road.turn.angle, STRAIGHT_ANGLE) <= 2 * NARROW_TURN_ANGLE &&
+               !hasRoundaboutType(road.turn.instruction) &&
+               angularDeviation(next_road.turn.angle, road.turn.angle) >
+                   std::numeric_limits<double>::epsilon();
+    };
+
+    bool hasNarrow =
+        std::find_if(intersection.begin(), intersection.end(), linkTest) != intersection.end();
+    if (!hasNarrow)
+        return intersection;
+
+    const auto source_edge_data = node_based_graph.GetEdgeData(source_edge_id);
+
+    const bool hasNext = obvious_turn_index != 0;
+    if (!hasNext)
+        return intersection;
+
+    // check whether the continue road is valid
+    const auto check_valid = [this, source_edge_data](const ConnectedRoad &road) {
+        const auto road_edge_data = node_based_graph.GetEdgeData(road.turn.eid);
+        // Test to see if the source edge and the one we're looking at are the same road
+        return road_edge_data.road_classification.road_class ==
+                   source_edge_data.road_classification.road_class &&
+               road_edge_data.name_id != EMPTY_NAMEID &&
+               road_edge_data.name_id == source_edge_data.name_id && road.entry_allowed;
+    };
+
+    if (!check_valid(next_road))
+        return intersection;
+
+    // Threshold check, if the intersection is too far away, don't bother continuing
+    const auto &next_road_data = node_based_graph.GetEdgeData(next_road.turn.eid);
+    if (next_road_data.distance > MAX_SLIPROAD_THRESHOLD)
+    {
+        return intersection;
+    }
+    auto next_intersection_node = node_based_graph.GetTarget(next_road.turn.eid);
+
+    const auto next_road_next_intersection = [&]() {
+        auto intersection = intersection_generator(intersection_node_id, next_road.turn.eid);
+        auto in_edge = next_road.turn.eid;
+        // skip over traffic lights
+        if (intersection.size() == 2)
+        {
+            const auto node = node_based_graph.GetTarget(in_edge);
+            in_edge = intersection[1].turn.eid;
+            next_intersection_node = node_based_graph.GetTarget(in_edge);
+            intersection = intersection_generator(node, in_edge);
+        }
+        return intersection;
+    }();
+
+    std::unordered_set<NameID> target_road_names;
+
+    for (const auto &road : next_road_next_intersection)
+    {
+        const auto &target_data = node_based_graph.GetEdgeData(road.turn.eid);
+        target_road_names.insert(target_data.name_id);
+    }
+
+    for (auto &road : intersection)
+    {
+        if (linkTest(road))
+        {
+            EdgeID candidate_in = road.turn.eid;
+            const auto target_intersection = [&](NodeID node) {
+                auto intersection = intersection_generator(node, candidate_in);
+                // skip over traffic lights
+                if (intersection.size() == 2)
+                {
+                    node = node_based_graph.GetTarget(candidate_in);
+                    candidate_in = intersection[1].turn.eid;
+                    intersection = intersection_generator(node, candidate_in);
+                }
+                return intersection;
+            }(intersection_node_id);
+
+            for (const auto &candidate_road : target_intersection)
+            {
+                const auto &candidate_data = node_based_graph.GetEdgeData(candidate_road.turn.eid);
+                if (target_road_names.count(candidate_data.name_id) > 0)
+                {
+                    if (node_based_graph.GetTarget(candidate_road.turn.eid) ==
+                        next_intersection_node)
+                    {
+                        road.turn.instruction.type = TurnType::Sliproad;
+                        break;
+                    }
+                    else
+                    {
+                        const auto skip_traffic_light_intersection =
+                            intersection_generator(node_based_graph.GetTarget(candidate_in), candidate_road.turn.eid);
+                        if (skip_traffic_light_intersection.size() == 2 &&
+                            node_based_graph.GetTarget(
+                                skip_traffic_light_intersection[1].turn.eid) ==
+                                next_intersection_node)
+                        {
+
+                            road.turn.instruction.type = TurnType::Sliproad;
+                            break;
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    if (next_road.turn.instruction.type == TurnType::Fork)
+    {
+        const auto &next_data = node_based_graph.GetEdgeData(next_road.turn.eid);
+        if (next_data.name_id == source_edge_data.name_id)
+        {
+            if (angularDeviation(next_road.turn.angle, STRAIGHT_ANGLE) < 5)
+                intersection[obvious_turn_index].turn.instruction.type = TurnType::Suppressed;
+            else
+                intersection[obvious_turn_index].turn.instruction.type = TurnType::Continue;
+            intersection[obvious_turn_index].turn.instruction.direction_modifier =
+                getTurnDirection(intersection[obvious_turn_index].turn.angle);
+        }
+        else if (next_data.name_id != EMPTY_NAMEID)
+        {
+            intersection[obvious_turn_index].turn.instruction.type = TurnType::NewName;
+            intersection[obvious_turn_index].turn.instruction.direction_modifier =
+                getTurnDirection(intersection[obvious_turn_index].turn.angle);
+        }
+        else
+        {
+            intersection[obvious_turn_index].turn.instruction.type = TurnType::Suppressed;
+        }
+    }
+
+    return intersection;
+}
+
+} // namespace guidance
+} // namespace extractor
+} // namespace osrm

src/extractor/guidance/turn_analysis.cpp

@@ -49,7 +49,12 @@ TurnAnalysis::TurnAnalysis(const util::NodeBasedDynamicGraph &node_based_graph,
                          name_table,
                          street_name_suffix_table),
       motorway_handler(node_based_graph, node_info_list, name_table, street_name_suffix_table),
-      turn_handler(node_based_graph, node_info_list, name_table, street_name_suffix_table)
+      turn_handler(node_based_graph, node_info_list, name_table, street_name_suffix_table),
+      sliproad_handler(intersection_generator,
+                       node_based_graph,
+                       node_info_list,
+                       name_table,
+                       street_name_suffix_table)
 {
 }
 
@@ -78,7 +83,7 @@ Intersection TurnAnalysis::assignTurnTypes(const NodeID from_nid,
         }
     }
     // Handle sliproads
-    intersection = handleSliproads(via_eid, std::move(intersection));
+    intersection = sliproad_handler(from_nid, via_eid, std::move(intersection));
 
     // Turn On Ramps Into Off Ramps, if we come from a motorway-like road
     if (isMotorwayClass(node_based_graph.GetEdgeData(via_eid).road_classification.road_class))
@@ -127,135 +132,6 @@ TurnAnalysis::setTurnTypes(const NodeID from_nid, const EdgeID, Intersection int
     return intersection;
 }
 
-// "Sliproads" occur when we've got a link between two roads (MOTORWAY_LINK, etc), but
-// the two roads are *also* directly connected shortly afterwards.
-// In these cases, we tag the turn-type as "sliproad", and then in post-processing
-// we emit a "turn", instead of "take the ramp"+"merge"
-Intersection TurnAnalysis::handleSliproads(const EdgeID source_edge_id,
-                                           Intersection intersection) const
-{
-    auto intersection_node_id = node_based_graph.GetTarget(source_edge_id);
-
-    const auto linkTest = [this](const ConnectedRoad &road) {
-        return !node_based_graph.GetEdgeData(road.turn.eid).roundabout && road.entry_allowed &&
-               angularDeviation(road.turn.angle, STRAIGHT_ANGLE) <= 2 * NARROW_TURN_ANGLE &&
-               !hasRoundaboutType(road.turn.instruction);
-    };
-
-    bool hasNarrow =
-        std::find_if(intersection.begin(), intersection.end(), linkTest) != intersection.end();
-    if (!hasNarrow)
-        return intersection;
-
-    const auto source_edge_data = node_based_graph.GetEdgeData(source_edge_id);
-
-    // Find the continuation of the intersection we're on
-    auto next_road = std::find_if(
-        intersection.begin(),
-        intersection.end(),
-        [this, source_edge_data](const ConnectedRoad &road) {
-            const auto road_edge_data = node_based_graph.GetEdgeData(road.turn.eid);
-            // Test to see if the source edge and the one we're looking at are the same road
-            return road_edge_data.road_classification.road_class ==
-                       source_edge_data.road_classification.road_class &&
-                   road_edge_data.name_id != EMPTY_NAMEID &&
-                   road_edge_data.name_id == source_edge_data.name_id && road.entry_allowed &&
-                   angularDeviation(road.turn.angle, STRAIGHT_ANGLE) < FUZZY_ANGLE_DIFFERENCE;
-        });
-
-    const bool hasNext = next_road != intersection.end();
-    if (!hasNext)
-    {
-        return intersection;
-    }
-
-    // Threshold check, if the intersection is too far away, don't bother continuing
-    const auto &next_road_data = node_based_graph.GetEdgeData(next_road->turn.eid);
-    if (next_road_data.distance > MAX_SLIPROAD_THRESHOLD)
-    {
-        return intersection;
-    }
-
-    auto next_intersection_node = node_based_graph.GetTarget(next_road->turn.eid);
-
-    const auto next_road_next_intersection = [&]() {
-        auto intersection = intersection_generator(intersection_node_id, next_road->turn.eid);
-        auto in_edge = next_road->turn.eid;
-        //skip over traffic lights
-        if(intersection.size() == 2)
-        {
-            const auto node = node_based_graph.GetTarget(in_edge);
-            in_edge = intersection[1].turn.eid;
-            next_intersection_node = node_based_graph.GetTarget(in_edge);
-            intersection = intersection_generator(node, in_edge);
-        }
-        return intersection;
-    }();
-
-    std::unordered_set<NameID> target_road_names;
-
-    for (const auto &road : next_road_next_intersection)
-    {
-        const auto &target_data = node_based_graph.GetEdgeData(road.turn.eid);
-        target_road_names.insert(target_data.name_id);
-    }
-
-    for (auto &road : intersection)
-    {
-        if (linkTest(road))
-        {
-            const auto target_intersection = [&](NodeID node, EdgeID eid) {
-                auto intersection = intersection_generator(node, eid);
-                //skip over traffic lights
-                if(intersection.size() == 2)
-                {
-                    node = node_based_graph.GetTarget(eid);
-                    eid = intersection[1].turn.eid;
-                    intersection = intersection_generator(node, eid);
-                }
-                return intersection;
-            }(intersection_node_id, road.turn.eid);
-
-            for (const auto &candidate_road : target_intersection)
-            {
-                const auto &candidate_data = node_based_graph.GetEdgeData(candidate_road.turn.eid);
-                if (target_road_names.count(candidate_data.name_id) > 0 &&
-                    node_based_graph.GetTarget(candidate_road.turn.eid) == next_intersection_node)
-                {
-                    road.turn.instruction.type = TurnType::Sliproad;
-                    break;
-                }
-            }
-        }
-    }
-
-    if (next_road->turn.instruction.type == TurnType::Fork)
-    {
-        const auto &next_data = node_based_graph.GetEdgeData(next_road->turn.eid);
-        if (next_data.name_id == source_edge_data.name_id)
-        {
-            if (angularDeviation(next_road->turn.angle, STRAIGHT_ANGLE) < 5)
-                next_road->turn.instruction.type = TurnType::Suppressed;
-            else
-                next_road->turn.instruction.type = TurnType::Continue;
-            next_road->turn.instruction.direction_modifier =
-                getTurnDirection(next_road->turn.angle);
-        }
-        else if (next_data.name_id != EMPTY_NAMEID)
-        {
-            next_road->turn.instruction.type = TurnType::NewName;
-            next_road->turn.instruction.direction_modifier =
-                getTurnDirection(next_road->turn.angle);
-        }
-        else
-        {
-            next_road->turn.instruction.type = TurnType::Suppressed;
-        }
-    }
-
-    return intersection;
-}
-
 const IntersectionGenerator &TurnAnalysis::getGenerator() const { return intersection_generator; }
 
 } // namespace guidance

src/extractor/guidance/turn_handler.cpp

@@ -29,32 +29,30 @@ TurnHandler::TurnHandler(const util::NodeBasedDynamicGraph &node_based_graph,
 {
 }
 
-TurnHandler::~TurnHandler() = default;
-
 bool TurnHandler::canProcess(const NodeID, const EdgeID, const Intersection &) const
 {
     return true;
 }
 
 Intersection TurnHandler::
-operator()(const NodeID, const EdgeID via_eid, Intersection intersection) const
+operator()(const NodeID, const EdgeID via_edge, Intersection intersection) const
 {
     if (intersection.size() == 1)
         return handleOneWayTurn(std::move(intersection));
 
     if (intersection[0].entry_allowed)
     {
-        intersection[0].turn.instruction = {findBasicTurnType(via_eid, intersection[0]),
+        intersection[0].turn.instruction = {findBasicTurnType(via_edge, intersection[0]),
                                             DirectionModifier::UTurn};
     }
 
     if (intersection.size() == 2)
-        return handleTwoWayTurn(via_eid, std::move(intersection));
+        return handleTwoWayTurn(via_edge, std::move(intersection));
 
     if (intersection.size() == 3)
-        return handleThreeWayTurn(via_eid, std::move(intersection));
+        return handleThreeWayTurn(via_edge, std::move(intersection));
 
-    return handleComplexTurn(via_eid, std::move(intersection));
+    return handleComplexTurn(via_edge, std::move(intersection));
 }
 
 Intersection TurnHandler::handleOneWayTurn(Intersection intersection) const
@@ -72,14 +70,11 @@ Intersection TurnHandler::handleTwoWayTurn(const EdgeID via_edge, Intersection i
     return intersection;
 }
 
-Intersection TurnHandler::handleThreeWayTurn(const EdgeID via_edge, Intersection intersection) const
+bool TurnHandler::isObviousOfTwo(const EdgeID via_edge,
+                                 const ConnectedRoad &road,
+                                 const ConnectedRoad &other) const
 {
     const auto &in_data = node_based_graph.GetEdgeData(via_edge);
-    const auto &first_data = node_based_graph.GetEdgeData(intersection[1].turn.eid);
-    const auto &second_data = node_based_graph.GetEdgeData(intersection[2].turn.eid);
-    BOOST_ASSERT(intersection[0].turn.angle < 0.001);
-    const auto isObviousOfTwo = [this, in_data](const ConnectedRoad road,
-                                                const ConnectedRoad other) {
     const auto first_class =
         node_based_graph.GetEdgeData(road.turn.eid).road_classification.road_class;
 
@@ -96,16 +91,15 @@ Intersection TurnHandler::handleThreeWayTurn(const EdgeID via_edge, Intersection
         return true;
 
     const bool other_is_obvious_by_road_class =
-            (!isRampClass(second_class) &&
-             (2 * getPriority(second_class) < getPriority(first_class)) &&
+        (!isRampClass(second_class) && (2 * getPriority(second_class) < getPriority(first_class)) &&
          in_data.road_classification.road_class == second_class) ||
         (!isLowPriorityRoadClass(second_class) && isLowPriorityRoadClass(first_class));
 
     if (other_is_obvious_by_road_class)
         return false;
 
-        const bool turn_is_perfectly_straight = angularDeviation(road.turn.angle, STRAIGHT_ANGLE) <
-                                                std::numeric_limits<double>::epsilon();
+    const bool turn_is_perfectly_straight =
+        angularDeviation(road.turn.angle, STRAIGHT_ANGLE) < std::numeric_limits<double>::epsilon();
 
     if (turn_is_perfectly_straight && in_data.name_id != EMPTY_NAMEID &&
         in_data.name_id == node_based_graph.GetEdgeData(road.turn.eid).name_id)
@@ -120,8 +114,14 @@ Intersection TurnHandler::handleThreeWayTurn(const EdgeID via_edge, Intersection
             FUZZY_ANGLE_DIFFERENCE;
 
     return is_much_narrower_than_other;
-    };
+};
 
+Intersection TurnHandler::handleThreeWayTurn(const EdgeID via_edge, Intersection intersection) const
+{
+    const auto &in_data = node_based_graph.GetEdgeData(via_edge);
+    const auto &first_data = node_based_graph.GetEdgeData(intersection[1].turn.eid);
+    const auto &second_data = node_based_graph.GetEdgeData(intersection[2].turn.eid);
+    BOOST_ASSERT(intersection[0].turn.angle < 0.001);
     /* Two nearly straight turns -> FORK
                OOOOOOO
              /
@@ -129,54 +129,10 @@ Intersection TurnHandler::handleThreeWayTurn(const EdgeID via_edge, Intersection
              \
                OOOOOOO
      */
-    if (isFork(intersection[0], intersection[1], intersection[2]))
-    {
-        if (intersection[1].entry_allowed && intersection[2].entry_allowed)
-        {
-            const auto left_class = node_based_graph.GetEdgeData(intersection[2].turn.eid)
-                                        .road_classification.road_class;
-            const auto right_class = node_based_graph.GetEdgeData(intersection[1].turn.eid)
-                                         .road_classification.road_class;
-            if (isObviousOfTwo(intersection[1], intersection[2]) &&
-                (second_data.name_id != in_data.name_id ||
-                 first_data.name_id == second_data.name_id))
-            {
-                intersection[1].turn.instruction =
-                    getInstructionForObvious(intersection.size(), via_edge, false, intersection[1]);
-                intersection[2].turn.instruction = {findBasicTurnType(via_edge, intersection[2]),
-                                                    DirectionModifier::SlightLeft};
-            }
-            else if (isObviousOfTwo(intersection[2], intersection[1]) &&
-                     (first_data.name_id != in_data.name_id ||
-                      first_data.name_id == second_data.name_id))
-            {
-                intersection[2].turn.instruction =
-                    getInstructionForObvious(intersection.size(), via_edge, false, intersection[2]);
-                intersection[1].turn.instruction = {findBasicTurnType(via_edge, intersection[1]),
-                                                    DirectionModifier::SlightRight};
-            }
-            else if (canBeSeenAsFork(left_class, right_class))
-            {
+    const auto fork_range = findFork(via_edge, intersection);
+    if (fork_range.first == 1 && fork_range.second == 2)
         assignFork(via_edge, intersection[2], intersection[1]);
-            }
-            else
-            {
-                intersection[1].turn.instruction = {findBasicTurnType(via_edge, intersection[1]),
-                                                    DirectionModifier::SlightRight};
-                intersection[2].turn.instruction = {findBasicTurnType(via_edge, intersection[2]),
-                                                    DirectionModifier::SlightLeft};
-            }
-        }
-        else
-        {
-            if (intersection[1].entry_allowed)
-                intersection[1].turn.instruction =
-                    getInstructionForObvious(intersection.size(), via_edge, false, intersection[1]);
-            if (intersection[2].entry_allowed)
-                intersection[2].turn.instruction =
-                    getInstructionForObvious(intersection.size(), via_edge, false, intersection[2]);
-        }
-    }
+
     /*  T Intersection
 
         OOOOOOO T OOOOOOOO
@@ -185,8 +141,8 @@ Intersection TurnHandler::handleThreeWayTurn(const EdgeID via_edge, Intersection
                 I
      */
     else if (isEndOfRoad(intersection[0], intersection[1], intersection[2]) &&
-             !isObviousOfTwo(intersection[1], intersection[2]) &&
-             !isObviousOfTwo(intersection[2], intersection[1]))
+             !isObviousOfTwo(via_edge, intersection[1], intersection[2]) &&
+             !isObviousOfTwo(via_edge, intersection[2], intersection[1]))
     {
         if (intersection[1].entry_allowed)
         {
@@ -206,7 +162,7 @@ Intersection TurnHandler::handleThreeWayTurn(const EdgeID via_edge, Intersection
     }
     else
     {
-        if (isObviousOfTwo(intersection[1], intersection[2]) &&
+        if (isObviousOfTwo(via_edge, intersection[1], intersection[2]) &&
             (in_data.name_id != second_data.name_id || first_data.name_id == second_data.name_id))
         {
             intersection[1].turn.instruction = getInstructionForObvious(
@@ -218,7 +174,7 @@ Intersection TurnHandler::handleThreeWayTurn(const EdgeID via_edge, Intersection
                                                 getTurnDirection(intersection[1].turn.angle)};
         }
 
-        if (isObviousOfTwo(intersection[2], intersection[1]) &&
+        if (isObviousOfTwo(via_edge, intersection[2], intersection[1]) &&
             (in_data.name_id != first_data.name_id || first_data.name_id == second_data.name_id))
         {
             intersection[2].turn.instruction = getInstructionForObvious(
@@ -236,7 +192,7 @@ Intersection TurnHandler::handleThreeWayTurn(const EdgeID via_edge, Intersection
 Intersection TurnHandler::handleComplexTurn(const EdgeID via_edge, Intersection intersection) const
 {
     const std::size_t obvious_index = findObviousTurn(via_edge, intersection);
-    const auto fork_range = findFork(intersection);
+    const auto fork_range = findFork(via_edge, intersection);
     std::size_t straightmost_turn = 0;
     double straightmost_deviation = 180;
     for (std::size_t i = 0; i < intersection.size(); ++i)
@@ -358,119 +314,6 @@ Intersection TurnHandler::handleComplexTurn(const EdgeID via_edge, Intersection
     return intersection;
 }
 
-std::size_t TurnHandler::findObviousTurn(const EdgeID via_edge,
-                                         const Intersection &intersection) const
-{
-    // no obvious road
-    if (intersection.size() == 1)
-        return 0;
-
-    // a single non u-turn is obvious
-    if (intersection.size() == 2)
-        return 1;
-
-    // at least three roads
-    std::size_t best = 0;
-    double best_deviation = 180;
-
-    std::size_t best_continue = 0;
-    double best_continue_deviation = 180;
-
-    const EdgeData &in_data = node_based_graph.GetEdgeData(via_edge);
-    const auto in_class = in_data.road_classification.road_class;
-    for (std::size_t i = 1; i < intersection.size(); ++i)
-    {
-        const double deviation = angularDeviation(intersection[i].turn.angle, STRAIGHT_ANGLE);
-        if (intersection[i].entry_allowed && deviation < best_deviation)
-        {
-            best_deviation = deviation;
-            best = i;
-        }
-
-        const auto out_data = node_based_graph.GetEdgeData(intersection[i].turn.eid);
-        auto continue_class = node_based_graph.GetEdgeData(intersection[best_continue].turn.eid)
-                                  .road_classification.road_class;
-        if (intersection[i].entry_allowed && out_data.name_id == in_data.name_id &&
-            (best_continue == 0 || (continue_class > out_data.road_classification.road_class &&
-                                    in_class != continue_class) ||
-             (deviation < best_continue_deviation &&
-              (out_data.road_classification.road_class == continue_class ||
-               in_class == out_data.road_classification.road_class))))
-        {
-            best_continue_deviation = deviation;
-            best_continue = i;
-        }
-    }
-
-    if (best == 0)
-        return 0;
-
-    if (best_deviation >= 2 * NARROW_TURN_ANGLE)
-        return 0;
-
-    // has no obvious continued road
-    if (best_continue == 0 || best_continue_deviation >= 2 * NARROW_TURN_ANGLE ||
-        (node_based_graph.GetEdgeData(intersection[best_continue].turn.eid)
-                 .road_classification.road_class ==
-             node_based_graph.GetEdgeData(intersection[best].turn.eid)
-                 .road_classification.road_class &&
-         std::abs(best_continue_deviation) > 1 && best_deviation / best_continue_deviation < 0.75))
-    {
-        // Find left/right deviation
-        const double left_deviation = angularDeviation(
-            intersection[(best + 1) % intersection.size()].turn.angle, STRAIGHT_ANGLE);
-        const double right_deviation =
-            angularDeviation(intersection[best - 1].turn.angle, STRAIGHT_ANGLE);
-
-        if (best_deviation < MAXIMAL_ALLOWED_NO_TURN_DEVIATION &&
-            std::min(left_deviation, right_deviation) > FUZZY_ANGLE_DIFFERENCE)
-            return best;
-
-        // other narrow turns?
-        if (angularDeviation(intersection[best - 1].turn.angle, STRAIGHT_ANGLE) <=
-            FUZZY_ANGLE_DIFFERENCE)
-            return 0;
-        if (angularDeviation(intersection[(best + 1) % intersection.size()].turn.angle,
-                             STRAIGHT_ANGLE) <= FUZZY_ANGLE_DIFFERENCE)
-            return 0;
-
-        // Well distinct turn that is nearly straight
-        if ((left_deviation / best_deviation >= DISTINCTION_RATIO ||
-             (left_deviation > best_deviation &&
-              !intersection[(best + 1) % intersection.size()].entry_allowed)) &&
-            (right_deviation / best_deviation >= DISTINCTION_RATIO ||
-             (right_deviation > best_deviation && !intersection[best - 1].entry_allowed)))
-        {
-            return best;
-        }
-    }
-    else
-    {
-        const double deviation =
-            angularDeviation(intersection[best_continue].turn.angle, STRAIGHT_ANGLE);
-        const auto &continue_data =
-            node_based_graph.GetEdgeData(intersection[best_continue].turn.eid);
-        if (std::abs(deviation) < 1)
-            return best_continue;
-
-        // check if any other similar best continues exist
-        for (std::size_t i = 1; i < intersection.size(); ++i)
-        {
-            if (i == best_continue || !intersection[i].entry_allowed)
-                continue;
-
-            if (angularDeviation(intersection[i].turn.angle, STRAIGHT_ANGLE) / deviation < 1.1 &&
-                continue_data.road_classification.road_class ==
-                    node_based_graph.GetEdgeData(intersection[i].turn.eid)
-                        .road_classification.road_class)
-                return 0;
-        }
-        return best_continue; // no obvious turn
-    }
-
-    return 0;
-}
-
 // Assignment of left turns hands of to right turns.
 // To do so, we mirror every road segment and reverse the order.
 // After the mirror and reversal / we assign right turns and
@@ -631,7 +474,8 @@ Intersection TurnHandler::assignRightTurns(const EdgeID via_edge,
     return intersection;
 }
 
-std::pair<std::size_t, std::size_t> TurnHandler::findFork(const Intersection &intersection) const
+std::pair<std::size_t, std::size_t> TurnHandler::findFork(const EdgeID via_edge,
+                                                          const Intersection &intersection) const
 {
 
     std::size_t best = 0;
@@ -650,39 +494,67 @@ std::pair<std::size_t, std::size_t> TurnHandler::findFork(const Intersection &in
     if (best_deviation <= NARROW_TURN_ANGLE)
     {
         std::size_t left = best, right = best;
-        if (intersection[best].turn.angle >= 180)
-        {
-            // due to best > 1, we can safely decrement right
-            --right;
-            if (angularDeviation(intersection[right].turn.angle, STRAIGHT_ANGLE) >
-                NARROW_TURN_ANGLE)
-                return std::make_pair(std::size_t{0}, std::size_t{0});
-        }
-        else
-        {
-            ++left;
-            if (left >= intersection.size() ||
-                angularDeviation(intersection[left].turn.angle, STRAIGHT_ANGLE) > NARROW_TURN_ANGLE)
-                return std::make_pair(std::size_t{0}, std::size_t{0});
-        }
         while (left + 1 < intersection.size() &&
-               angularDeviation(intersection[left].turn.angle, intersection[left + 1].turn.angle) <
-                   NARROW_TURN_ANGLE &&
-               angularDeviation(intersection[left].turn.angle, STRAIGHT_ANGLE) <= GROUP_ANGLE)
+               (angularDeviation(intersection[left + 1].turn.angle, STRAIGHT_ANGLE) <=
+                    NARROW_TURN_ANGLE ||
+                (angularDeviation(intersection[left].turn.angle,
+                                  intersection[left + 1].turn.angle) <= NARROW_TURN_ANGLE &&
+                 angularDeviation(intersection[left].turn.angle, STRAIGHT_ANGLE) <= GROUP_ANGLE)))
             ++left;
-        while (right > 1 &&
-               angularDeviation(intersection[right].turn.angle,
-                                intersection[right - 1].turn.angle) < NARROW_TURN_ANGLE &&
-               angularDeviation(intersection[right - 1].turn.angle, STRAIGHT_ANGLE) <= GROUP_ANGLE)
+        while (
+            right > 1 &&
+            (angularDeviation(intersection[right - 1].turn.angle, STRAIGHT_ANGLE) <=
+                 NARROW_TURN_ANGLE ||
+             (angularDeviation(intersection[right].turn.angle, intersection[right - 1].turn.angle) <
+                  NARROW_TURN_ANGLE &&
+              angularDeviation(intersection[right - 1].turn.angle, STRAIGHT_ANGLE) <= GROUP_ANGLE)))
             --right;
 
-        // TODO check whether 2*NARROW_TURN is too large
-        if (0 < right && right < left &&
+        if (left == right)
+            return std::make_pair(std::size_t{0}, std::size_t{0});
+
+        const bool valid_indices = 0 < right && right < left;
+        const bool separated_at_left_side =
             angularDeviation(intersection[left].turn.angle,
                              intersection[(left + 1) % intersection.size()].turn.angle) >=
-                GROUP_ANGLE &&
+            GROUP_ANGLE;
+        const bool separated_at_right_side =
+            right > 0 &&
             angularDeviation(intersection[right].turn.angle, intersection[right - 1].turn.angle) >=
-                GROUP_ANGLE)
+                GROUP_ANGLE;
+
+        const bool not_more_than_three = (left - right) <= 2;
+        const bool has_obvious = [&]() {
+            if (left - right == 1)
+            {
+                return isObviousOfTwo(via_edge, intersection[left], intersection[right]) ||
+                       isObviousOfTwo(via_edge, intersection[right], intersection[left]);
+            }
+            else if (left - right == 2)
+            {
+                return isObviousOfTwo(via_edge, intersection[right + 1], intersection[right]) ||
+                       isObviousOfTwo(via_edge, intersection[right], intersection[right + 1]) ||
+                       isObviousOfTwo(via_edge, intersection[left], intersection[right + 1]) ||
+                       isObviousOfTwo(via_edge, intersection[right + 1], intersection[left]);
+            }
+            return false;
+        }();
+
+        const bool has_compatible_classes = [&]() {
+            const bool ramp_class =
+                isLinkClass(node_based_graph.GetEdgeData(intersection[right].turn.eid)
+                                .road_classification.road_class);
+            for (std::size_t index = right + 1; index <= left; ++index)
+                if (ramp_class !=
+                    isLinkClass(node_based_graph.GetEdgeData(intersection[index].turn.eid)
+                                    .road_classification.road_class))
+                    return false;
+            return true;
+        }();
+
+        // TODO check whether 2*NARROW_TURN is too large
+        if (valid_indices && separated_at_left_side && separated_at_right_side &&
+            not_more_than_three && !has_obvious && has_compatible_classes)
             return std::make_pair(right, left);
     }
     return std::make_pair(std::size_t{0}, std::size_t{0});