From 31d2c4a15f2229f4496ef5ae0059fc69af54746c Mon Sep 17 00:00:00 2001
From: Josh Bendavid <Josh.Bendavid@cern.ch>
Date: Tue, 17 Jan 2023 00:52:24 +0100
Subject: [PATCH] re-initialize geometry in g4e propagator as required at
 beginning of propagation and for each step

---
 TrackPropagation/Geant4e/src/Geant4ePropagator.cc | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/TrackPropagation/Geant4e/src/Geant4ePropagator.cc b/TrackPropagation/Geant4e/src/Geant4ePropagator.cc
index 54852ac133027..42f1418322925 100644
--- a/TrackPropagation/Geant4e/src/Geant4ePropagator.cc
+++ b/TrackPropagation/Geant4e/src/Geant4ePropagator.cc
@@ -30,6 +30,7 @@
 #include "G4TransportationManager.hh"
 #include "G4Tubs.hh"
 #include "G4UImanager.hh"
+#include "G4ErrorPropagationNavigator.hh"
 
 // CLHEP
 #include "CLHEP/Units/GlobalSystemOfUnits.h"
@@ -311,11 +312,18 @@ std::pair<TrajectoryStateOnSurface, double> Geant4ePropagator::propagateGeneric(
 
   theG4eManager->InitTrackPropagation();
 
+  // re-initialize navigator to avoid mismatches and/or segfaults
+  theG4eManager->GetErrorPropagationNavigator()->LocateGlobalPointAndSetup(
+      g4InitPos, &g4InitMom, /*pRelativeSearch = */ false, /*ignoreDirection = */ false);
+
   bool continuePropagation = true;
   while (continuePropagation) {
     iterations++;
     LogDebug("Geant4e") << std::endl << "step count " << iterations << " step length " << finalPathLength;
 
+    // re-initialize navigator to avoid mismatches and/or segfaults
+    theG4eManager->GetErrorPropagationNavigator()->LocateGlobalPointWithinVolume(g4eTrajState.GetPosition());
+
     const int ierr = theG4eManager->PropagateOneStep(&g4eTrajState, mode);
 
     if (ierr != 0) {