feat: Angles of incidence in neural calibrator (#2494)

As stated in #2493, angles of incidence are more useful than global frame direction for calibration purposes, so in the PR we add feed these to the neural calibrator instead.

depends on #2493

Examples/Framework/ML/src/NeuralCalibrator.cpp

@@ -8,6 +8,7 @@
 
 #include "Acts/EventData/SourceLink.hpp"
 #include "Acts/Utilities/CalibrationContext.hpp"
+#include "Acts/Utilities/UnitVectors.hpp"
 #include <ActsExamples/EventData/NeuralCalibrator.hpp>
 
 #include <TFile.h>
@@ -96,8 +97,8 @@ void ActsExamples::NeuralCalibrator::calibrate(
 
   input[iInput++] = idxSourceLink.geometryId().volume();
   input[iInput++] = idxSourceLink.geometryId().layer();
-  input[iInput++] = trackState.parameters()[Acts::eBoundPhi];
-  input[iInput++] = trackState.parameters()[Acts::eBoundTheta];
+
+  const Acts::Surface& referenceSurface = trackState.referenceSurface();
 
   std::visit(
       [&](const auto& measurement) {
@@ -107,6 +108,24 @@ void ActsExamples::NeuralCalibrator::calibrate(
         Acts::ActsSquareMatrix<Acts::eBoundSize> fcov =
             E * measurement.covariance() * E.transpose();
 
+        Acts::Vector3 dir = Acts::makeDirectionFromPhiTheta(
+            fpar[Acts::eBoundPhi], fpar[Acts::eBoundTheta]);
+        Acts::Vector3 globalPosition = referenceSurface.localToGlobal(
+            gctx, fpar.segment<2>(Acts::eBoundLoc0), dir);
+
+        // Rotation matrix. When applied to global coordinates, they
+        // are rotated into the local reference frame of the
+        // surface. Note that this such a rotation can be found by
+        // inverting a matrix whose columns correspond to the
+        // coordinate axes of the local coordinate system.
+        Acts::RotationMatrix3 rot =
+            referenceSurface.referenceFrame(gctx, globalPosition, dir)
+                .inverse();
+        std::pair<double, double> angles =
+            Acts::VectorHelpers::incidentAngles(dir, rot);
+
+        input[iInput++] = angles.first;
+        input[iInput++] = angles.second;
         input[iInput++] = fpar[Acts::eBoundLoc0];
         input[iInput++] = fpar[Acts::eBoundLoc1];
         input[iInput++] = fcov(Acts::eBoundLoc0, Acts::eBoundLoc0);