Possibility to bias magnetic field origin via env.var.

Common/Field/CMakeLists.txt

@@ -16,6 +16,7 @@ o2_add_library(Field
                        src/MagFieldParam.cxx
                        src/MagneticField.cxx
                        src/MagneticWrapperChebyshev.cxx
+                       src/FieldOriginBiasParam.cxx
                        src/ALICE3MagneticField.cxx
                        PUBLIC_LINK_LIBRARIES O2::MathUtils FairRoot::Base O2::CommonUtils)
 
@@ -26,6 +27,7 @@ o2_target_root_dictionary(Field
                                   include/Field/MagFieldContFact.h
                                   include/Field/MagFieldFast.h
                                   include/Field/MagFieldFact.h
+                                  include/Field/FieldOriginBiasParam.h
                                   include/Field/ALICE3MagneticField.h)
 
 o2_add_test(MagneticField

Common/Field/include/Field/FieldOriginBiasParam.h

@@ -0,0 +1,38 @@
+// Copyright 2019-2026 CERN and copyright holders of ALICE O2.
+// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
+// All rights not expressly granted are reserved.
+//
+// This software is distributed under the terms of the GNU General Public
+// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
+//
+// In applying this license CERN does not waive the privileges and immunities
+// granted to it by virtue of its status as an Intergovernmental Organization
+// or submit itself to any jurisdiction.
+
+/// \author ruben.shahoyan@cern.ch
+
+/// parameters to bias the origin of the magnetic field
+
+#ifndef ALICEO2_FIELDORIGIN_BIAS_PARAM_H
+#define ALICEO2_FIELDORIGIN_BIAS_PARAM_H
+
+#include "CommonUtils/ConfigurableParam.h"
+#include "CommonUtils/ConfigurableParamHelper.h"
+
+namespace o2
+{
+namespace field
+{
+
+struct FieldOriginBiasParam : public o2::conf::ConfigurableParamHelper<FieldOriginBiasParam> {
+  double x = 0.;
+  double y = 0.;
+  double z = 0.;
+
+  O2ParamDef(FieldOriginBiasParam, "FieldOriginBias");
+};
+
+} // namespace field
+} // end namespace o2
+
+#endif

Common/Field/include/Field/MagneticField.h

@@ -32,6 +32,7 @@ namespace o2
 namespace field
 {
 class MagneticWrapperChebyshev;
+class FieldOriginBiasParam;
 }
 } // namespace o2
 namespace o2
@@ -249,6 +250,7 @@ class MagneticField : public FairField
   void setBeamType(MagFieldParam::BeamType_t type) { mBeamType = type; }
 
   void setBeamEnergy(float energy) { mBeamEnergy = energy; }
+  void checkOriginBias();
 
  private:
   std::unique_ptr<MagneticWrapperChebyshev> mMeasuredMap; //! Measured part of the field map
@@ -273,6 +275,8 @@ class MagneticField : public FairField
 
   TNamed mParameterNames; ///< file and parameterization loaded
 
+  static const FieldOriginBiasParam* gOriginBias;
+
   static const Double_t sSolenoidToDipoleZ;  ///< conventional Z of transition from L3 to Dipole field
   static const UShort_t sPolarityConvention; ///< convention for the mapping of the curr.sign on main component sign
 

Common/Field/src/FieldLinkDef.h

@@ -22,4 +22,7 @@
 #pragma link C++ class o2::field::MagFieldFast + ;
 #pragma link C++ class o2::field::ALICE3MagneticField + ;
 
+#pragma link C++ class o2::field::FieldOriginBiasParam + ;
+#pragma link C++ class o2::conf::ConfigurableParamHelper < o2::field::FieldOriginBiasParam> + ;
+
 #endif

Common/Field/src/FieldOriginBiasParam.cxx

@@ -0,0 +1,18 @@
+// Copyright 2019-2026 CERN and copyright holders of ALICE O2.
+// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
+// All rights not expressly granted are reserved.
+//
+// This software is distributed under the terms of the GNU General Public
+// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
+//
+// In applying this license CERN does not waive the privileges and immunities
+// granted to it by virtue of its status as an Intergovernmental Organization
+// or submit itself to any jurisdiction.
+
+/// \author ruben.shahoyan@cern.ch
+
+/// parameters to bias the origin of the magnetic field
+
+#include "Field/FieldOriginBiasParam.h"
+
+O2ParamImpl(o2::field::FieldOriginBiasParam);

Common/Field/src/MagneticField.cxx

@@ -14,6 +14,7 @@
 /// \author ruben.shahoyan@cern.ch
 
 #include "Field/MagneticField.h"
+#include "Field/FieldOriginBiasParam.h"
 #include <TFile.h>             // for TFile
 #include <TPRegexp.h>          // for TPRegexp
 #include <TString.h>           // for TString
@@ -27,6 +28,8 @@ using namespace o2::field;
 
 ClassImp(MagneticField);
 
+const FieldOriginBiasParam* MagneticField::gOriginBias = nullptr;
+
 const Double_t MagneticField::sSolenoidToDipoleZ = -700.;
 
 /// Explanation for polarity conventions: these are the mapping between the
@@ -88,6 +91,9 @@ MagneticField::MagneticField()
    * Default constructor
    */
   fType = 2; // flag non-constant field
+  if (!gOriginBias) {
+    checkOriginBias();
+  }
 }
 
 MagneticField::MagneticField(const char* name, const char* title, Double_t factorSol, Double_t factorDip,
@@ -116,8 +122,10 @@ MagneticField::MagneticField(const char* name, const char* title, Double_t facto
   /*
    * Constructor for human readable params
    */
-
   setDataFileName(path.c_str());
+  if (!gOriginBias) {
+    checkOriginBias();
+  }
   CreateField();
 }
 
@@ -145,8 +153,10 @@ MagneticField::MagneticField(const MagFieldParam& param)
   /*
    * Constructor for FairParam derived params
    */
-
   setDataFileName(param.GetMapPath());
+  if (!gOriginBias) {
+    checkOriginBias();
+  }
   CreateField();
 }
 
@@ -261,12 +271,12 @@ Bool_t MagneticField::loadParameterization()
   return kTRUE;
 }
 
-void MagneticField::Field(const Double_t* __restrict__ xyz, Double_t* __restrict__ b)
+void MagneticField::Field(const Double_t* __restrict__ xyzExt, Double_t* __restrict__ b)
 {
   /*
    * query field value at point
    */
-
+  double xyz[3] = {xyzExt[0] - gOriginBias->x, xyzExt[1] - gOriginBias->y, xyzExt[2] - gOriginBias->z};
   //  b[0]=b[1]=b[2]=0.0;
   if (mFastField && mFastField->Field(xyz, b)) {
     return;
@@ -288,12 +298,12 @@ void MagneticField::Field(const Double_t* __restrict__ xyz, Double_t* __restrict
   }
 }
 
-Double_t MagneticField::getBz(const Double_t* xyz) const
+Double_t MagneticField::getBz(const Double_t* xyzExt) const
 {
   /*
    * query field Bz component at point
    */
-
+  double xyz[3] = {xyzExt[0] - gOriginBias->x, xyzExt[1] - gOriginBias->y, xyzExt[2] - gOriginBias->z};
   if (mFastField) {
     double bz = 0;
     if (mFastField->GetBz(xyz, bz)) {
@@ -728,3 +738,14 @@ void MagneticField::AllowFastField(bool v)
     mFastField.reset(nullptr);
   }
 }
+
+//_____________________________________________________________________________
+void MagneticField::checkOriginBias()
+{
+  // posibility to globally bias all data members with the proper env.var
+  if (const auto* biasString = std::getenv("O2_DPL_FIELDORIGINBIAS"); biasString && *biasString) {
+    o2::conf::ConfigurableParam::updateFromString(biasString);
+  }
+  gOriginBias = &FieldOriginBiasParam::Instance();
+  LOGP(info, "Field origin is set to: XYZ: {:.4f},{:.4f},{:.4f}", gOriginBias->x, gOriginBias->y, gOriginBias->z);
+}