feat: Smearing for straw surfaces (#3197)

This PR introduces the smearing of the` boundParameters` of Straw Surface, that can be used for a fast digitization approach for the MDTs with a Gaussian distribution. It is configures from the json structure that can be used for the creation of a json file for a full propagation-digitization test.
Also the option for positive only values is introduced in the `SmearingConfig` as a flag because for the case of the drift radius we want to get only positive values as output.

Examples/Algorithms/Digitization/include/ActsExamples/Digitization/SmearingConfig.hpp

@@ -21,6 +21,8 @@ struct ParameterSmearingConfig {
   Acts::BoundIndices index = Acts::eBoundSize;
   /// The smearing function for this parameter.
   ActsFatras::SingleParameterSmearFunction<RandomEngine> smearFunction;
+  /// A flag to return only positive smeared values
+  bool forcePositiveValues = false;
 };
 
 // The configured indices must be unique, i.e. each one can only appear once

Fatras/include/ActsFatras/Digitization/UncorrelatedHitSmearer.hpp

@@ -49,6 +49,7 @@ struct BoundParametersSmearer {
   /// Parameter indices that will be used to create the smeared measurements.
   std::array<Acts::BoundIndices, kSize> indices{};
   std::array<SingleParameterSmearFunction<generator_t>, kSize> smearFunctions{};
+  std::array<bool, kSize> forcePositive = {};
 
   static constexpr std::size_t size() { return kSize; }
 
@@ -93,6 +94,9 @@ struct BoundParametersSmearer {
       }
       auto [value, stddev] = res.value();
       par[i] = value;
+      if (forcePositive[i]) {
+        par[i] = std::abs(value);
+      }
       cov(i, i) = stddev * stddev;
     }
 

Tests/UnitTests/Fatras/Digitization/CMakeLists.txt

@@ -1,4 +1,4 @@
-set(unittest_extra_libraries ActsFatras)
+set(unittest_extra_libraries ActsExamplesDigitization ActsExamplesIoJson ActsFatras)
 
 add_unittest(FatrasChannelMerger ChannelMergerTests.cpp)
 add_unittest(FatrasChannelizer ChannelizerTests.cpp)

Tests/UnitTests/Fatras/Digitization/UncorrelatedHitSmearerTests.cpp

@@ -18,9 +18,13 @@
 #include "Acts/Geometry/GeometryContext.hpp"
 #include "Acts/Geometry/GeometryIdentifier.hpp"
 #include "Acts/Surfaces/PlaneSurface.hpp"
+#include "Acts/Surfaces/StrawSurface.hpp"
 #include "Acts/Surfaces/Surface.hpp"
 #include "Acts/Tests/CommonHelpers/FloatComparisons.hpp"
 #include "Acts/Utilities/Result.hpp"
+#include "ActsExamples/Digitization/DigitizationConfigurator.hpp"
+#include "ActsExamples/Digitization/Smearers.hpp"
+#include "ActsExamples/Io/Json/JsonDigitizationConfig.hpp"
 #include "ActsFatras/Digitization/DigitizationError.hpp"
 #include "ActsFatras/Digitization/UncorrelatedHitSmearer.hpp"
 #include "ActsFatras/EventData/Barcode.hpp"
@@ -37,6 +41,8 @@
 #include <random>
 #include <utility>
 
+#include <nlohmann/json.hpp>
+
 namespace {
 
 namespace bd = boost::unit_test::data;
@@ -69,8 +75,9 @@ struct InvalidSmearer {
   }
 };
 
+template <typename generator_t>
 struct Fixture {
-  RandomGenerator rng;
+  generator_t rng;
   // identifiers
   Acts::GeometryIdentifier gid;
   ActsFatras::Barcode pid;
@@ -83,13 +90,12 @@ struct Fixture {
   // hit information
   ActsFatras::Hit hit;
 
-  Fixture(uint64_t rngSeed)
+  Fixture(uint64_t rngSeed, std::shared_ptr<Acts::Surface> surf)
       : rng(rngSeed),
         gid(Acts::GeometryIdentifier().setVolume(1).setLayer(2).setSensitive(
             3)),
         pid(ActsFatras::Barcode().setVertexPrimary(12).setParticle(23)),
-        surface(Acts::Surface::makeShared<Acts::PlaneSurface>(
-            Acts::Transform3(Acts::Translation3(3, 2, 1)))) {
+        surface(std::move(surf)) {
     using namespace Acts::UnitLiterals;
     using Acts::VectorHelpers::makeVector4;
 
@@ -99,6 +105,7 @@ struct Fixture {
     auto [par, cov] =
         Acts::detail::Test::generateBoundParametersCovariance(rng);
     boundParams = par;
+
     freeParams =
         Acts::transformBoundToFreeParameters(*surface, geoCtx, boundParams);
 
@@ -135,7 +142,9 @@ constexpr auto tol = 128 * std::numeric_limits<double>::epsilon();
 BOOST_AUTO_TEST_SUITE(FatrasUncorrelatedHitSmearer)
 
 BOOST_DATA_TEST_CASE(Bound1, bd::make(boundIndices), index) {
-  Fixture f(123);
+  Fixture<RandomGenerator> f(
+      123, Acts::Surface::makeShared<Acts::PlaneSurface>(
+               Acts::Transform3(Acts::Translation3(3, 2, 1))));
   ActsFatras::BoundParametersSmearer<RandomGenerator, 1u> s;
   s.indices = {index};
 
@@ -165,7 +174,9 @@ BOOST_DATA_TEST_CASE(Bound1, bd::make(boundIndices), index) {
 }
 
 BOOST_AUTO_TEST_CASE(BoundAll) {
-  Fixture f(12356);
+  Fixture<RandomGenerator> f(
+      12356, Acts::Surface::makeShared<Acts::PlaneSurface>(
+                 Acts::Transform3(Acts::Translation3(3, 2, 1))));
   // without q/p
   ActsFatras::BoundParametersSmearer<RandomGenerator, std::size(boundIndices)>
       s;
@@ -209,7 +220,9 @@ BOOST_AUTO_TEST_CASE(BoundAll) {
 }
 
 BOOST_DATA_TEST_CASE(Free1, bd::make(freeIndices), index) {
-  Fixture f(1234);
+  Fixture<RandomGenerator> f(
+      1234, Acts::Surface::makeShared<Acts::PlaneSurface>(
+                Acts::Transform3(Acts::Translation3(3, 2, 1))));
   ActsFatras::FreeParametersSmearer<RandomGenerator, 1u> s;
   s.indices = {index};
 
@@ -239,7 +252,9 @@ BOOST_DATA_TEST_CASE(Free1, bd::make(freeIndices), index) {
 }
 
 BOOST_AUTO_TEST_CASE(FreeAll) {
-  Fixture f(123567);
+  Fixture<RandomGenerator> f(
+      123567, Acts::Surface::makeShared<Acts::PlaneSurface>(
+                  Acts::Transform3(Acts::Translation3(3, 2, 1))));
   // without q/p
   ActsFatras::FreeParametersSmearer<RandomGenerator, std::size(freeIndices)> s;
   std::copy(std::begin(freeIndices), std::end(freeIndices), s.indices.begin());
@@ -280,4 +295,62 @@ BOOST_AUTO_TEST_CASE(FreeAll) {
   }
 }
 
+BOOST_AUTO_TEST_CASE(GaussianSmearing) {
+  nlohmann::json djson = nlohmann::json::parse(R"(
+    {
+    "acts-geometry-hierarchy-map" : {
+    "format-version" : 0,
+    "value-identifier" : "digitization-configuration"
+    },
+    
+  "entries"
+      : [
+        {
+           "volume" : 1,
+           "value" : {
+            "smearing" : [
+              {"index" : 0, "mean" : 0.0, "stddev" : 0.05, "type" : "Gauss", "forcePositiveValues" : true}
+             
+             
+            ]
+          }
+        }
+      ]
+})");
+  double radius = 5.;
+  double halfZ = 8.;
+  Fixture<ActsExamples::RandomEngine> f(
+      123567,
+      Acts::Surface::makeShared<Acts::StrawSurface>(
+          Acts::Transform3(Acts::Translation3(0., 0., 0.)), radius, halfZ));
+
+  // Get the smearing configuration from the json object
+  auto digiConfig =
+      ActsExamples::DigiConfigConverter("digitization-configuration")
+          .fromJson(djson);
+  ActsFatras::BoundParametersSmearer<ActsExamples::RandomEngine, 1u> s;
+
+  for (auto& el : digiConfig) {
+    for (auto& smearing : el.smearingDigiConfig) {
+      std::fill(std::begin(s.indices), std::end(s.indices),
+                static_cast<Acts::BoundIndices>(smearing.index));
+      std::fill(std::begin(s.smearFunctions), std::end(s.smearFunctions),
+                smearing.smearFunction);
+      std::fill(std::begin(s.forcePositive), std::end(s.forcePositive),
+                smearing.forcePositiveValues);
+    }
+  }
+
+  auto ret = s(f.rng, f.hit, *f.surface, f.geoCtx);
+
+  BOOST_CHECK(ret.ok());
+  auto [par, cov] = ret.value();
+  for (std::size_t i = 0; i < s.indices.size(); i++) {
+    BOOST_TEST_INFO("Comparing smeared measurement "
+                    << i << " originating from bound parameter "
+                    << s.indices[i]);
+    CHECK_CLOSE_REL(par[i], f.boundParams[s.indices[i]], 0.15);
+  }
+}
+
 BOOST_AUTO_TEST_SUITE_END()