feat: Add ability to skip grid bins in SP grouping and add ITk "fast"…

… tracking config for seeding (#2166)

This PR adds the ITk fastTracking configuration for the seeding, which includes:
- A new feature in `binnedSPGroup` that allow us to skip z bins for middle SPs in the search for neighbours SPs
- A new flag in the python ITk configuration for high occupancy seeding

Core/include/Acts/Seeding/BinnedSPGroup.hpp

@@ -64,11 +64,11 @@ class BinnedSPGroupIterator {
   void findNotEmptyBin();
 
  private:
-  /// The group, it contains the grid and the bin finders
+  // The group, it contains the grid and the bin finders
   Acts::detail::RefHolder<BinnedSPGroup<external_spacepoint_t>> m_group;
-  /// Max Local Bins - limits of the grid
+  // Max Local Bins - limits of the grid
   std::array<std::size_t, 2> m_max_localBins;
-  /// Current Local Bins
+  // Current Local Bins
   std::array<std::size_t, 2> m_current_localBins{0, 0};
 };
 
@@ -113,6 +113,10 @@ class BinnedSPGroup {
     return *m_grid.get();
   }
 
+  std::size_t skipZMiddleBin() {
+    return m_skipZMiddleBin;
+  }
+
  private:
   // grid with ownership of all InternalSpacePoint
   std::unique_ptr<Acts::SpacePointGrid<external_spacepoint_t>> m_grid;
@@ -122,7 +126,10 @@ class BinnedSPGroup {
   std::shared_ptr<const BinFinder<external_spacepoint_t>> m_topBinFinder;
   std::shared_ptr<const BinFinder<external_spacepoint_t>> m_bottomBinFinder;
 
+  // Order of z bins to loop over when searching for SPs
   std::vector<size_t> m_bins;
+  // Number of Z bins to skip the search for middle SP
+  std::size_t m_skipZMiddleBin;
 };
 
 }  // namespace Acts

Core/include/Acts/Seeding/BinnedSPGroup.ipp

@@ -15,6 +15,7 @@ Acts::BinnedSPGroupIterator<external_spacepoint_t>::BinnedSPGroupIterator(
     Acts::BinnedSPGroup<external_spacepoint_t>& group, std::size_t index)
     : m_group(group), m_max_localBins(m_group->m_grid->numLocalBins()) {
   m_max_localBins[INDEX::PHI] += 1;
+  m_current_localBins[INDEX::Z] = m_group->skipZMiddleBin();
   if (index == m_group->m_grid->size()) {
     m_current_localBins = m_max_localBins;
   } else {
@@ -30,7 +31,7 @@ Acts::BinnedSPGroupIterator<external_spacepoint_t>::operator++() {
   // if we were on the edge, go up one phi bin and reset z bin
   if (++m_current_localBins[INDEX::Z] == m_max_localBins[INDEX::Z]) {
     ++m_current_localBins[INDEX::PHI];
-    m_current_localBins[INDEX::Z] = 0;
+    m_current_localBins[INDEX::Z] = m_group->skipZMiddleBin();
   }
 
   // Get the next not-empty bin in the grid
@@ -94,7 +95,6 @@ Acts::BinnedSPGroupIterator<external_spacepoint_t>::findNotEmptyBin() {
       std::size_t zBinIndex = m_group->m_bins[zBin];
       std::size_t index =
           m_group->m_grid->globalBinFromLocalBins({phiBin, zBinIndex});
-
       // Check if there are entries in this bin
       if (m_group->m_grid->at(index).empty()) {
         continue;
@@ -106,7 +106,7 @@ Acts::BinnedSPGroupIterator<external_spacepoint_t>::findNotEmptyBin() {
       return;
     }
     // Reset z-index
-    m_current_localBins[INDEX::Z] = 0;
+    m_current_localBins[INDEX::Z] = m_group->skipZMiddleBin();
   }
 
   // Could find nothing ... setting this to end()
@@ -172,6 +172,7 @@ Acts::BinnedSPGroup<external_spacepoint_t>::BinnedSPGroup(
     // store x,y,z values in extent
     rRangeSPExtent.extend({spX, spY, spZ});
 
+    // remove SPs outside z and phi region
     if (spZ > zMax || spZ < zMin) {
       continue;
     }
@@ -219,6 +220,7 @@ Acts::BinnedSPGroup<external_spacepoint_t>::BinnedSPGroup(
   m_bottomBinFinder = botBinFinder;
   m_topBinFinder = tBinFinder;
 
+  m_skipZMiddleBin = config.skipZMiddleBinSearch;
   m_bins = config.zBinsCustomLooping;
   if (m_bins.empty()) {
     std::size_t nZbins = m_grid->numLocalBins()[1];

Core/include/Acts/Seeding/SeedFinderConfig.hpp

@@ -57,6 +57,10 @@ struct SeedFinderConfig {
   float rMinMiddle = 60.f * Acts::UnitConstants::mm;
   float rMaxMiddle = 120.f * Acts::UnitConstants::mm;
 
+  // z of last layers to avoid iterations
+  std::pair<float, float> zOutermostLayers{-2700 * Acts::UnitConstants::mm,
+                                           2700 * Acts::UnitConstants::mm};
+
   // cut to the maximum value of delta z between SPs
   float deltaZMax =
       std::numeric_limits<float>::infinity() * Acts::UnitConstants::mm;
@@ -116,11 +120,10 @@ struct SeedFinderConfig {
   // which will make seeding very slow!
   float rMin = 33 * Acts::UnitConstants::mm;
 
-  // z of last layers to avoid iterations
-  std::pair<float, float> zOutermostLayers{-2700 * Acts::UnitConstants::mm,
-                                           2700 * Acts::UnitConstants::mm};
-
+  // Order of z bins to loop over when searching for SPs
   std::vector<size_t> zBinsCustomLooping = {};
+  // Number of Z bins to skip the search for middle SPs
+  std::size_t skipZMiddleBinSearch = 0;
 
   // average radiation lengths of material on the length of a seed. used for
   // scattering.

Examples/Algorithms/TrackFinding/src/SeedingAlgorithm.cpp

@@ -229,8 +229,9 @@ ActsExamples::ProcessCode ActsExamples::SeedingAlgorithm::execute(
   spacePointPtrs.reserve(nSpacePoints);
   for (const auto& isp : m_inputSpacePoints) {
     for (const auto& spacePoint : (*isp)(ctx)) {
-      // since the event store owns the space points, their pointers should be
-      // stable and we do not need to create local copies.
+      // since the event store owns the space
+      // points, their pointers should be stable and
+      // we do not need to create local copies.
       spacePointPtrs.push_back(&spacePoint);
     }
   }

Examples/Python/python/acts/examples/itk.py

@@ -298,7 +298,9 @@ def buildITkGeometry(
     )
 
 
-def itkSeedingAlgConfig(inputSpacePointsType: InputSpacePointsType):
+def itkSeedingAlgConfig(
+    inputSpacePointsType: InputSpacePointsType, highOccupancyConfig=False
+):
     assert isinstance(inputSpacePointsType, InputSpacePointsType)
 
     # variables that do not change for pixel and strip SPs:
@@ -309,7 +311,7 @@ def itkSeedingAlgConfig(inputSpacePointsType: InputSpacePointsType):
     collisionRegionMin = -200 * u.mm
     collisionRegionMax = 200 * u.mm
     maxSeedsPerSpM = 4
-    cotThetaMax = 27.2899
+    cotThetaMax = 27.2899  # (4.0 eta) --> 27.2899 = 1/tan(2*arctan(exp(-4)))
     sigmaScattering = 2
     radLengthPerSeed = 0.0975
     minPt = 900 * u.MeV
@@ -439,6 +441,14 @@ def itkSeedingAlgConfig(inputSpacePointsType: InputSpacePointsType):
         maxSeedsPerSpMConf = 5
         maxQualitySeedsPerSpMConf = 5
         useDeltaRorTopRadius = True
+
+        if highOccupancyConfig == True:
+            rMaxGridConfig = 250 * u.mm
+            deltaRMax = 200 * u.mm
+            zBinsCustomLooping = [1, 11, 2, 10, 3, 9, 6, 4, 8, 5, 7]
+            # variables that are only used for highOccupancyConfig configuration:
+            skipZMiddleBinSearch = 2
+
     elif inputSpacePointsType is InputSpacePointsType.StripSpacePoints:
         outputSeeds = "StripSeeds"
         allowSeparateRMax = True
@@ -491,6 +501,27 @@ def itkSeedingAlgConfig(inputSpacePointsType: InputSpacePointsType):
         maxQualitySeedsPerSpMConf = 100
         useDeltaRorTopRadius = False
 
+    if highOccupancyConfig == True:
+        minPt = 1000 * u.MeV
+        collisionRegionMin = -150 * u.mm
+        collisionRegionMax = 150 * u.mm
+        rRangeMiddleSP = [
+            [40.0, 80.0],
+            [40.0, 200.0],
+            [70.0, 200.0],
+            [70.0, 200.0],
+            [70.0, 250.0],
+            [70.0, 250.0],
+            [70.0, 250.0],
+            [70.0, 200.0],
+            [70.0, 200.0],
+            [40.0, 200.0],
+            [40.0, 80.0],
+        ]
+        useVariableMiddleSPRange = False
+    else:
+        skipZMiddleBinSearch = 0
+
     # fill namedtuples
     seedFinderConfigArg = SeedFinderConfigArg(
         maxSeedsPerSpM=maxSeedsPerSpM,
@@ -506,6 +537,7 @@ def itkSeedingAlgConfig(inputSpacePointsType: InputSpacePointsType):
         maxPtScattering=maxPtScattering,
         zBinEdges=zBinEdges,
         zBinsCustomLooping=zBinsCustomLooping,
+        skipZMiddleBinSearch=skipZMiddleBinSearch,
         rRangeMiddleSP=rRangeMiddleSP,
         useVariableMiddleSPRange=useVariableMiddleSPRange,
         binSizeR=binSizeR,
@@ -538,6 +570,7 @@ def itkSeedingAlgConfig(inputSpacePointsType: InputSpacePointsType):
     )
     spacePointGridConfigArg = SpacePointGridConfigArg(
         rMax=rMaxGridConfig,
+        deltaRMax=deltaRMax,
         zBinEdges=zBinEdges,
         phiBinDeflectionCoverage=phiBinDeflectionCoverage,
         phi=(phiMin, phiMax),

Examples/Python/python/acts/examples/reconstruction.py

@@ -41,6 +41,7 @@
         "maxPtScattering",
         "zBinEdges",
         "zBinsCustomLooping",
+        "skipZMiddleBinSearch",
         "rRangeMiddleSP",
         "useVariableMiddleSPRange",
         "binSizeR",
@@ -56,7 +57,7 @@
         "z",  # (min,max)
         "zOutermostLayers",  # (min,max)
     ],
-    defaults=[None] * 19 + [(None, None)] * 8,
+    defaults=[None] * 20 + [(None, None)] * 8,
 )
 SeedFinderOptionsArg = namedtuple(
     "SeedFinderOptions", ["beamPos", "bFieldInZ"], defaults=[(None, None), None]
@@ -201,7 +202,7 @@ def addSeeding(
     initialVarInflation : list
         List of 6 scale factors to inflate the initial covariance matrix
         Defaults specified in Examples/Algorithms/TrackFinding/include/ActsExamples/TrackFinding/TrackParamsEstimationAlgorithm.hpp
-    seedFinderConfigArg : SeedFinderConfigArg(maxSeedsPerSpM, cotThetaMax, sigmaScattering, radLengthPerSeed, minPt, impactMax, deltaPhiMax, interactionPointCut, arithmeticAverageCotTheta, deltaZMax, maxPtScattering, zBinEdges, zBinsCustomLooping, rRangeMiddleSP, useVariableMiddleSPRange, binSizeR, seedConfirmation, centralSeedConfirmationRange, forwardSeedConfirmationRange, deltaR, deltaRBottomSP, deltaRTopSP, deltaRMiddleSPRange, collisionRegion, r, z, zOutermostLayers)
+    seedFinderConfigArg : SeedFinderConfigArg(maxSeedsPerSpM, cotThetaMax, sigmaScattering, radLengthPerSeed, minPt, impactMax, deltaPhiMax, interactionPointCut, arithmeticAverageCotTheta, deltaZMax, maxPtScattering, zBinEdges, zBinsCustomLooping, skipZMiddleBinSearch, rRangeMiddleSP, useVariableMiddleSPRange, binSizeR, seedConfirmation, centralSeedConfirmationRange, forwardSeedConfirmationRange, deltaR, deltaRBottomSP, deltaRTopSP, deltaRMiddleSPRange, collisionRegion, r, z, zOutermostLayers)
         SeedFinderConfig settings. deltaR, deltaRBottomSP, deltaRTopSP, deltaRMiddleSPRange, collisionRegion, r, z, zOutermostLayers are ranges specified as a tuple of (min,max). beamPos is specified as (x,y).
         Defaults specified in Core/include/Acts/Seeding/SeedFinderConfig.hpp
     seedFinderOptionsArg :  SeedFinderOptionsArg(bFieldInZ, beamPos)
@@ -544,6 +545,7 @@ def addStandardSeeding(
             maxPtScattering=seedFinderConfigArg.maxPtScattering,
             zBinEdges=seedFinderConfigArg.zBinEdges,
             zBinsCustomLooping=seedFinderConfigArg.zBinsCustomLooping,
+            skipZMiddleBinSearch=seedFinderConfigArg.skipZMiddleBinSearch,
             rRangeMiddleSP=seedFinderConfigArg.rRangeMiddleSP,
             useVariableMiddleSPRange=seedFinderConfigArg.useVariableMiddleSPRange,
             binSizeR=seedFinderConfigArg.binSizeR,

Examples/Python/src/TrackFinding.cpp

@@ -123,6 +123,7 @@ void addTrackFinding(Context& ctx) {
     ACTS_PYTHON_MEMBER(zBinEdges);
     ACTS_PYTHON_MEMBER(interactionPointCut);
     ACTS_PYTHON_MEMBER(zBinsCustomLooping);
+    ACTS_PYTHON_MEMBER(skipZMiddleBinSearch);
     ACTS_PYTHON_MEMBER(useVariableMiddleSPRange);
     ACTS_PYTHON_MEMBER(deltaRMiddleMinSPRange);
     ACTS_PYTHON_MEMBER(deltaRMiddleMaxSPRange);