refactor!: Remove bFieldMin from estimateTrackParamsFromSeed (#3863)

This parameter does not have any benefit for the implementation or interface. The user might have checked or guarantees that the magnetic field is strong enough. At the same time we will check for `NaN`s at the end. For this reason I propose to remove this parameter to keep the interface clean and concise.

Core/include/Acts/Seeding/EstimateTrackParamsFromSeed.hpp

@@ -18,7 +18,6 @@
 
 #include <array>
 #include <cmath>
-#include <iostream>
 #include <iterator>
 #include <optional>
 #include <stdexcept>
@@ -126,36 +125,21 @@ FreeVector estimateTrackParamsFromSeed(spacepoint_range_t spRange,
 /// @param surface is the surface of the bottom space point. The estimated bound
 /// track parameters will be represented also at this surface
 /// @param bField is the magnetic field vector
-/// @param bFieldMin is the minimum magnetic field required to trigger the
-/// estimation of q/pt
 /// @param logger A logger instance
 ///
 /// @return optional bound parameters
 template <typename spacepoint_iterator_t>
 std::optional<BoundVector> estimateTrackParamsFromSeed(
     const GeometryContext& gctx, spacepoint_iterator_t spBegin,
     spacepoint_iterator_t spEnd, const Surface& surface, const Vector3& bField,
-    ActsScalar bFieldMin, const Acts::Logger& logger = getDummyLogger()) {
+    const Acts::Logger& logger = getDummyLogger()) {
   // Check the number of provided space points
   std::size_t numSP = std::distance(spBegin, spEnd);
   if (numSP != 3) {
     ACTS_ERROR("There should be exactly three space points provided.");
     return std::nullopt;
   }
 
-  // Convert bField to Tesla
-  ActsScalar bFieldStrength = bField.norm();
-  // Check if magnetic field is too small
-  if (bFieldStrength < bFieldMin) {
-    // @todo shall we use straight-line estimation and use default q/pt in such
-    // case?
-    ACTS_WARNING(
-        "The magnetic field at the bottom space point: B = "
-        << bFieldStrength / UnitConstants::T << " T is smaller than |B|_min = "
-        << bFieldMin / UnitConstants::T << " T. Estimation is not performed.");
-    return std::nullopt;
-  }
-
   // The global positions of the bottom, middle and space points
   std::array<Vector3, 3> spGlobalPositions = {Vector3::Zero(), Vector3::Zero(),
                                               Vector3::Zero()};
@@ -252,6 +236,7 @@ std::optional<BoundVector> estimateTrackParamsFromSeed(
   params[eBoundLoc1] = bottomLocalPos.y();
   params[eBoundTime] = spGlobalTimes[0].value_or(0.);
 
+  ActsScalar bFieldStrength = bField.norm();
   // The estimated q/pt in [GeV/c]^-1 (note that the pt is the projection of
   // momentum on the transverse plane of the new frame)
   ActsScalar qOverPt = sign / (bFieldStrength * R);

Examples/Algorithms/TrackFinding/src/TrackParamsEstimationAlgorithm.cpp

@@ -112,10 +112,16 @@ ProcessCode TrackParamsEstimationAlgorithm::execute(
     }
     Acts::Vector3 field = *fieldRes;
 
+    if (field.norm() < m_cfg.bFieldMin) {
+      ACTS_WARNING("Magnetic field at seed " << iseed << " is too small "
+                                             << field.norm());
+      continue;
+    }
+
     // Estimate the track parameters from seed
     auto optParams = Acts::estimateTrackParamsFromSeed(
         ctx.geoContext, seed.sp().begin(), seed.sp().end(), *surface, field,
-        m_cfg.bFieldMin, logger());
+        logger());
     if (!optParams.has_value()) {
       ACTS_WARNING("Estimation of track parameters for seed " << iseed
                                                               << " failed.");

Examples/Algorithms/TrackFindingExaTrkX/src/PrototracksToParameters.cpp

@@ -154,16 +154,21 @@ ProcessCode PrototracksToParameters::execute(
                            .geometryId();
     const auto &surface = *m_cfg.geometry->findSurface(geoId);
 
-    auto field = m_cfg.magneticField->getField(
+    auto fieldRes = m_cfg.magneticField->getField(
         {bottomSP->x(), bottomSP->y(), bottomSP->z()}, bCache);
-    if (!field.ok()) {
-      ACTS_ERROR("Field lookup error: " << field.error());
+    if (!fieldRes.ok()) {
+      ACTS_ERROR("Field lookup error: " << fieldRes.error());
       return ProcessCode::ABORT;
     }
+    Acts::Vector3 field = *fieldRes;
+
+    if (field.norm() < m_cfg.bFieldMin) {
+      ACTS_WARNING("Magnetic field at seed is too small " << field.norm());
+      continue;
+    }
 
     auto pars = Acts::estimateTrackParamsFromSeed(
-        ctx.geoContext, seed.sp().begin(), seed.sp().end(), surface, *field,
-        m_cfg.bFieldMin);
+        ctx.geoContext, seed.sp().begin(), seed.sp().end(), surface, field);
 
     if (not pars) {
       ACTS_WARNING("Skip track because of bad params");

Examples/Algorithms/TruthTracking/ActsExamples/TruthTracking/ParticleSmearing.cpp

@@ -10,21 +10,15 @@
 
 #include "Acts/Definitions/Algebra.hpp"
 #include "Acts/Definitions/TrackParametrization.hpp"
-#include "Acts/EventData/ParticleHypothesis.hpp"
 #include "Acts/Seeding/EstimateTrackParamsFromSeed.hpp"
 #include "Acts/Surfaces/PerigeeSurface.hpp"
 #include "Acts/Surfaces/Surface.hpp"
-#include "Acts/Utilities/Helpers.hpp"
 #include "Acts/Utilities/detail/periodic.hpp"
 #include "ActsExamples/EventData/SimParticle.hpp"
 #include "ActsExamples/EventData/Track.hpp"
 #include "ActsExamples/Framework/AlgorithmContext.hpp"
 #include "ActsExamples/Framework/RandomNumbers.hpp"
-#include "ActsExamples/Utilities/GroupBy.hpp"
-#include "ActsExamples/Utilities/Range.hpp"
-#include "ActsFatras/EventData/Particle.hpp"
 
-#include <algorithm>
 #include <cmath>
 #include <ostream>
 #include <random>

Tests/UnitTests/Core/Seeding/EstimateTrackParamsFromSeedTest.cpp

@@ -176,7 +176,7 @@ BOOST_AUTO_TEST_CASE(trackparameters_estimation_test) {
           // Test the bound track parameters estimator
           auto fullParamsOpt = estimateTrackParamsFromSeed(
               geoCtx, spacePointPtrs.begin(), spacePointPtrs.end(),
-              *bottomSurface, bField, 0.1_T, *logger);
+              *bottomSurface, bField, *logger);
           BOOST_REQUIRE(fullParamsOpt.has_value());
           const auto& estFullParams = fullParamsOpt.value();
           BOOST_TEST_INFO(