slic_mag_field_debug.cxx

    auto vec = step->GetPreStepPoint()->GetPosition();
    const double pos[] = {vec[0], vec[1], vec[2]};
    double bfield[] = {0, 0, 0, 0};
    G4StepPoint* pre = step->GetPreStepPoint();
    G4FieldManager* globalFieldMgr = G4TransportationManager::GetTransportationManager()-> GetFieldManager();
    globalFieldMgr->GetDetectorField()->GetFieldValue(pos, bfield);
    std::cout << ">>>> Field val: " << pre->GetPosition() << " -> ("
                << bfield[0] << ", " << bfield[1] << ", " << bfield[2] << ") " << std::endl;