add low precision intersection_generator mode for faster graph traversal

include/extractor/guidance/coordinate_extractor.hpp

@@ -49,6 +49,17 @@ class CoordinateExtractor
     std::vector<util::Coordinate> GetForwardCoordinatesAlongRoad(const NodeID from,
                                                                  const EdgeID turn_edge) const;
 
+    // a less precise way to compute coordinates along a route. Due to the heavy interaction of
+    // graph traversal and turn instructions, we often don't care for high precision. We only want
+    // to check for available connections in order, or find (with room for error) the straightmost
+    // turn. This function will offer a bit more error potential but allow for much higher
+    // performance
+    OSRM_ATTR_WARN_UNUSED
+    util::Coordinate GetCoordinateCloseToTurn(const NodeID from_node,
+                                              const EdgeID turn_edge,
+                                              const bool traversed_in_reverse,
+                                              const NodeID to_node) const;
+
     /* When extracting the coordinates, we first extract all coordinates. We don't care about most
      * of them, though.
      *

include/extractor/guidance/intersection_generator.hpp

@@ -51,8 +51,14 @@ class IntersectionGenerator
     // Check for restrictions/barriers and generate a list of valid and invalid turns present at
     // the node reached from `from_node` via `via_eid`. The resulting candidates have to be analysed
     // for their actual instructions later on.
+    // The switch for `use_low_precision_angles` enables a faster mode that will procude less
+    // accurate coordinates. It should be good enough to check order of turns, find striaghtmost
+    // turns. Even good enough to do some simple angle verifications. It is mostly available to
+    // allow for faster graph traversal in the extraction phase.
     OSRM_ATTR_WARN_UNUSED
-    Intersection GetConnectedRoads(const NodeID from_node, const EdgeID via_eid) const;
+    Intersection GetConnectedRoads(const NodeID from_node,
+                                   const EdgeID via_eid,
+                                   const bool use_low_precision_angles = false) const;
 
   private:
     const util::NodeBasedDynamicGraph &node_based_graph;