feat: Closest forward intersection (acts-project#2923)

Implements closest forward order and renames `forwardOrder` to `pathLengthOrder`

Core/include/Acts/Utilities/Intersection.hpp

@@ -72,10 +72,10 @@ class Intersection {
 
   constexpr static Intersection invalid() { return Intersection(); }
 
-  /// Comparison function for forward order i.e. intersection closest to -inf
-  /// will be first.
-  constexpr static bool forwardOrder(const Intersection& aIntersection,
-                                     const Intersection& bIntersection) {
+  /// Comparison function for path length order i.e. intersection closest to
+  /// -inf will be first.
+  constexpr static bool pathLengthOrder(const Intersection& aIntersection,
+                                        const Intersection& bIntersection) {
     auto a = aIntersection.pathLength();
     auto b = bIntersection.pathLength();
     return a < b;
@@ -99,6 +99,16 @@ class Intersection {
     return std::abs(a) < std::abs(b);
   }
 
+  /// Comparison function for closest forward order i.e. intersection closest to
+  /// 0 with positive path length will be first.
+  constexpr static bool closestForwardOrder(const Intersection& aIntersection,
+                                            const Intersection& bIntersection) {
+    auto a = aIntersection.pathLength();
+    auto b = bIntersection.pathLength();
+    return std::signbit(a) == std::signbit(b) ? std::abs(a) < std::abs(b)
+                                              : a > b;
+  }
+
  private:
   /// Position of the intersection
   Position m_position = Position::Zero();
@@ -157,10 +167,11 @@ class ObjectIntersection {
 
   constexpr static ObjectIntersection invalid() { return ObjectIntersection(); }
 
-  constexpr static bool forwardOrder(const ObjectIntersection& aIntersection,
-                                     const ObjectIntersection& bIntersection) {
-    return Intersection3D::forwardOrder(aIntersection.intersection(),
-                                        bIntersection.intersection());
+  constexpr static bool pathLengthOrder(
+      const ObjectIntersection& aIntersection,
+      const ObjectIntersection& bIntersection) {
+    return Intersection3D::pathLengthOrder(aIntersection.intersection(),
+                                           bIntersection.intersection());
   }
 
   constexpr static bool closestOrder(const ObjectIntersection& aIntersection,
@@ -169,6 +180,13 @@ class ObjectIntersection {
                                         bIntersection.intersection());
   }
 
+  constexpr static bool closestForwardOrder(
+      const ObjectIntersection& aIntersection,
+      const ObjectIntersection& bIntersection) {
+    return Intersection3D::closestForwardOrder(aIntersection.intersection(),
+                                               bIntersection.intersection());
+  }
+
  private:
   /// The intersection itself
   Intersection3D m_intersection = Intersection3D::invalid();
@@ -218,6 +236,13 @@ class ObjectMultiIntersection {
                              ObjectIntersection<object_t>::closestOrder);
   }
 
+  constexpr ObjectIntersection<object_t> closestForward() const {
+    auto splitIntersections = split();
+    return *std::min_element(splitIntersections.begin(),
+                             splitIntersections.end(),
+                             ObjectIntersection<object_t>::closestForwardOrder);
+  }
+
  private:
   /// The intersections
   MultiIntersection3D m_intersections;

Core/src/Digitization/PlanarModuleStepper.cpp

@@ -63,7 +63,7 @@ std::vector<Acts::DigitizationStep> Acts::PlanarModuleStepper::cellSteps(
       Intersection3D(endPoint, (startPoint - endPoint).norm(),
                      Intersection3D::Status::reachable));
   std::sort(stepIntersections.begin(), stepIntersections.end(),
-            Intersection3D::forwardOrder);
+            Intersection3D::pathLengthOrder);
 
   Vector3 lastPosition = startPoint;
   // reserve the right amount
@@ -121,7 +121,7 @@ std::vector<Acts::DigitizationStep> Acts::PlanarModuleStepper::cellSteps(
         "More than 2 Boundary Surfaces intersected, this is an edge "
         "case, resolving ... ");
     std::sort(boundaryIntersections.begin(), boundaryIntersections.end(),
-              Intersection3D::forwardOrder);
+              Intersection3D::pathLengthOrder);
   }
   // if for some reason the intersection does not work
   if (boundaryIntersections.empty()) {

Core/src/Geometry/GenericApproachDescriptor.cpp

@@ -43,7 +43,7 @@ Acts::SurfaceIntersection Acts::GenericApproachDescriptor::approachSurface(
     return SurfaceIntersection::invalid();
   }
   return *std::min_element(sIntersections.begin(), sIntersections.end(),
-                           SurfaceIntersection::forwardOrder);
+                           SurfaceIntersection::pathLengthOrder);
 }
 
 const std::vector<const Acts::Surface*>&

Core/src/Geometry/Layer.cpp

@@ -252,7 +252,7 @@ Acts::Layer::compatibleSurfaces(
 
   // sort according to the path length
   std::sort(sIntersections.begin(), sIntersections.end(),
-            SurfaceIntersection::forwardOrder);
+            SurfaceIntersection::pathLengthOrder);
 
   return sIntersections;
 }

Core/src/Geometry/TrackingVolume.cpp

@@ -626,7 +626,7 @@ Acts::TrackingVolume::compatibleLayers(
     }
     std::sort(lIntersections.begin(), lIntersections.end(),
               [](const LayerIntersection& a, const LayerIntersection& b) {
-                return SurfaceIntersection::forwardOrder(a.first, b.first);
+                return SurfaceIntersection::pathLengthOrder(a.first, b.first);
               });
   }
   // and return
@@ -709,7 +709,7 @@ Acts::TrackingVolume::compatibleSurfacesFromHierarchy(
 
   // Sort according to the path length
   std::sort(sIntersections.begin(), sIntersections.end(),
-            SurfaceIntersection::forwardOrder);
+            SurfaceIntersection::pathLengthOrder);
 
   return sIntersections;
 }

Fatras/src/Digitization/PlanarSurfaceMask.cpp

@@ -58,7 +58,7 @@ Acts::Result<ActsFatras::PlanarSurfaceMask::Segment2D> maskAndReturn(
     std::vector<Acts::Intersection2D>& intersections,
     const ActsFatras::PlanarSurfaceMask::Segment2D& segment, bool firstInside) {
   std::sort(intersections.begin(), intersections.end(),
-            Acts::Intersection2D::forwardOrder);
+            Acts::Intersection2D::pathLengthOrder);
   if (intersections.size() >= 2) {
     return ActsFatras::PlanarSurfaceMask::Segment2D{
         intersections[0].position(), intersections[1].position()};

Tests/UnitTests/Core/Geometry/BVHDataTestCase.hpp

@@ -71,7 +71,7 @@ BOOST_DATA_TEST_CASE(
   }
 
   // sort by path length
-  std::sort(hits.begin(), hits.end(), SurfaceIntersection::forwardOrder);
+  std::sort(hits.begin(), hits.end(), SurfaceIntersection::pathLengthOrder);
   std::vector<const Surface*> expHits;
   expHits.reserve(hits.size());
   for (const auto& hit : hits) {

Tests/UnitTests/Core/Utilities/IntersectionTests.cpp

@@ -52,7 +52,7 @@ BOOST_AUTO_TEST_CASE(IntersectionTest) {
 
   // let's sort the tsf intersection, it should give fst
   std::sort(tsfpIntersections.begin(), tsfpIntersections.end(),
-            Intersection3D::forwardOrder);
+            Intersection3D::pathLengthOrder);
   BOOST_CHECK_EQUAL(fstpIntersections[0].pathLength(),
                     tsfpIntersections[0].pathLength());
   BOOST_CHECK_EQUAL(fstpIntersections[1].pathLength(),
@@ -67,7 +67,7 @@ BOOST_AUTO_TEST_CASE(IntersectionTest) {
 
   // shuffle the intersections
   std::sort(ntfspIntersections.begin(), ntfspIntersections.end(),
-            Intersection3D::forwardOrder);
+            Intersection3D::pathLengthOrder);
   BOOST_CHECK_EQUAL(fstpIntersections[0].pathLength(),
                     ntfspIntersections[0].pathLength());
   BOOST_CHECK_EQUAL(fstpIntersections[1].pathLength(),
@@ -76,7 +76,7 @@ BOOST_AUTO_TEST_CASE(IntersectionTest) {
                     ntfspIntersections[2].pathLength());
 
   std::sort(tfnsnpIntersections.begin(), tfnsnpIntersections.end(),
-            Intersection3D::forwardOrder);
+            Intersection3D::pathLengthOrder);
   BOOST_CHECK_EQUAL(fstpIntersections[0].pathLength(),
                     tfnsnpIntersections[0].pathLength());
   BOOST_CHECK_EQUAL(fstpIntersections[1].pathLength(),
@@ -97,7 +97,7 @@ BOOST_AUTO_TEST_CASE(IntersectionTest) {
 
   // this time around, sort the f-s-t-n to match the t-s-f-n
   std::sort(fstnIntersections.begin(), fstnIntersections.end(),
-            Intersection3D::forwardOrder);
+            Intersection3D::pathLengthOrder);
   BOOST_CHECK_EQUAL(fstnIntersections[0].pathLength(),
                     tsfnIntersections[0].pathLength());
   BOOST_CHECK_EQUAL(fstnIntersections[1].pathLength(),
@@ -108,7 +108,7 @@ BOOST_AUTO_TEST_CASE(IntersectionTest) {
   // shuffle negative and positive solutions
   std::vector<Intersection3D> pnsolutions = {tIp, sIn, sIp, fIn, tIn, fIp};
   std::sort(pnsolutions.begin(), pnsolutions.end(),
-            Intersection3D::forwardOrder);
+            Intersection3D::pathLengthOrder);
 
   BOOST_CHECK_EQUAL(pnsolutions[0].pathLength(), -3.);
   BOOST_CHECK_EQUAL(pnsolutions[1].pathLength(), -2.);
@@ -122,7 +122,7 @@ BOOST_AUTO_TEST_CASE(IntersectionTest) {
   std::vector<Intersection3D> tszfpIntersections = {tIp, sIp, zI, fIp};
 
   std::sort(tszfpIntersections.begin(), tszfpIntersections.end(),
-            Intersection3D::forwardOrder);
+            Intersection3D::pathLengthOrder);
   BOOST_CHECK_EQUAL(tszfpIntersections[0].pathLength(), 0.);
   BOOST_CHECK_EQUAL(tszfpIntersections[1].pathLength(), 1.);
   BOOST_CHECK_EQUAL(tszfpIntersections[2].pathLength(), 2.);
@@ -132,7 +132,7 @@ BOOST_AUTO_TEST_CASE(IntersectionTest) {
   std::vector<Intersection3D> ztfsnIntersections = {zI, tIn, fIn, sIn};
 
   std::sort(tfsznIntersections.begin(), tfsznIntersections.end(),
-            Intersection3D::forwardOrder);
+            Intersection3D::pathLengthOrder);
   BOOST_CHECK_EQUAL(tfsznIntersections[0].pathLength(), -3.);
   BOOST_CHECK_EQUAL(tfsznIntersections[1].pathLength(), -2.);
   BOOST_CHECK_EQUAL(tfsznIntersections[2].pathLength(), -1.);
@@ -184,7 +184,7 @@ BOOST_AUTO_TEST_CASE(ObjectIntersectionTest) {
   // This should give 6 different intersections
   std::set_union(firstSet.begin(), firstSet.end(), secondSet.begin(),
                  secondSet.end(), std::back_inserter(unionSetStd),
-                 PlaneIntersection::forwardOrder);
+                 PlaneIntersection::pathLengthOrder);
   BOOST_CHECK_EQUAL(unionSetStd.size(), 6u);
 }