new functions for FT0 to reconstruct event plane

Author: junleekim

Detectors/FIT/FT0/base/include/FT0Base/Geometry.h

@@ -65,9 +65,16 @@ class Geometry
     return o2::base::GeometryManager::getPNEntry(getDetID(), index);
   }
 
+  // Calculate the coordinates of all the channels.
+  void calculateChannelCenter();
+  // Get the coordinates of the center of the channel channelId.
+  TVector3 getChannelCenter(UInt_t channelId) {return mChannelCenter[channelId];}
+
  private:
   TVector3 mMCP[52];
   TVector3 mAngles[28];
+  std::array<TVector3, Nchannels> mChannelCenter;  /// Center of each channel in FT0 A (96) and C (112) combined.
+
 
   ClassDefNV(Geometry, 2);
 };

Detectors/FIT/FT0/base/src/Geometry.cxx

@@ -117,3 +117,78 @@ void Geometry::setCsideModules()
     mMCP[i + NCellsA].SetXYZ(xc2[i], yc2[i], zc2[i]);
   }
 }
+void Geometry::calculateChannelCenter()
+{
+  // This method calculates the position of each channel center composing both FT0-A
+  // and FT0-C, based on the position of their corresponding modules given by
+  // "Geometry::setAsideModules()" and "Geometry::setCsideModules()".
+
+  // Ensure the positions of the modules are well defined.
+  setAsideModules();
+  setCsideModules();
+
+  // Calculate first the positions for the channels for FT0-A. These correspond to the
+  // channels 0-95 in the modules mMCP[0-23].
+  Double_t delta = 5.3/4.;              // Half-channel width (TODO: ask if it actually corresponds to ChannelWidth)
+  Double_t xLocalChannels[Nchannels];   // x-positions of all channels ordered according to xi and internal numbering.
+  Double_t yLocalChannels[Nchannels];   // y-positions of all channels ordered according to yi and internal numbering.
+  Double_t zLocalChannels[Nchannels];   // z-positions of all channels ordered according to zi and internal numbering.
+                                        // INFO: We assume here the modules are perpendicular to z, so z(channel) = z(module).
+
+  for (int iModA = 0; iModA < NCellsA; iModA++) {
+    xLocalChannels[4*iModA+0] = mMCP[iModA].X() - delta;
+    xLocalChannels[4*iModA+1] = mMCP[iModA].X() + delta;
+    xLocalChannels[4*iModA+2] = mMCP[iModA].X() - delta;
+    xLocalChannels[4*iModA+3] = mMCP[iModA].X() + delta;
+
+    yLocalChannels[4*iModA+0] = mMCP[iModA].Y() + delta;
+    yLocalChannels[4*iModA+1] = mMCP[iModA].Y() + delta;
+    yLocalChannels[4*iModA+2] = mMCP[iModA].Y() - delta;
+    yLocalChannels[4*iModA+3] = mMCP[iModA].Y() - delta;
+
+    zLocalChannels[4*iModA+0] = mMCP[iModA].Z();
+    zLocalChannels[4*iModA+1] = mMCP[iModA].Z();
+    zLocalChannels[4*iModA+2] = mMCP[iModA].Z();
+    zLocalChannels[4*iModA+3] = mMCP[iModA].Z();
+  }
+
+  // Calculate then the positions for the channels for FT0-C, corresponding to the
+  // channels 96-207 in the modules mMCP[24-51].
+  for (int iModC = 0; iModC < NCellsC; iModC++) {
+    xLocalChannels[4*(iModC+NCellsA)+0] = mMCP[iModC+NCellsA].X() - delta;
+    xLocalChannels[4*(iModC+NCellsA)+1] = mMCP[iModC+NCellsA].X() + delta;
+    xLocalChannels[4*(iModC+NCellsA)+2] = mMCP[iModC+NCellsA].X() - delta;
+    xLocalChannels[4*(iModC+NCellsA)+3] = mMCP[iModC+NCellsA].X() + delta;
+
+    yLocalChannels[4*(iModC+NCellsA)+0] = mMCP[iModC+NCellsA].Y() + delta;
+    yLocalChannels[4*(iModC+NCellsA)+1] = mMCP[iModC+NCellsA].Y() + delta;
+    yLocalChannels[4*(iModC+NCellsA)+2] = mMCP[iModC+NCellsA].Y() - delta;
+    yLocalChannels[4*(iModC+NCellsA)+3] = mMCP[iModC+NCellsA].Y() - delta;
+
+    zLocalChannels[4*(iModC+NCellsA)+0] = mMCP[iModC+NCellsA].Z();
+    zLocalChannels[4*(iModC+NCellsA)+1] = mMCP[iModC+NCellsA].Z();
+    zLocalChannels[4*(iModC+NCellsA)+2] = mMCP[iModC+NCellsA].Z();
+    zLocalChannels[4*(iModC+NCellsA)+3] = mMCP[iModC+NCellsA].Z();
+  }
+
+  // Convert the local ordering of the channels to the official one and apply it to the channel map.
+  // localChannelOrder[local channel index] = official channel.
+    Int_t localChannelOrder[Nchannels] = {
+      58, 56, 59, 57, 54, 52, 55, 53, 50, 49, 51, 48, 47, 45, 46, 44, 43, 42, 41, 40,
+      61, 60, 63, 62, 14, 12, 15, 13, 10, 9, 11, 8, 7, 6, 5, 4, 39, 38, 37, 36,
+      65, 64, 66, 67, 17, 16, 18, 19, 3, 2, 0, 1, 35, 34, 32, 33,
+      68, 69, 70, 71, 20, 21, 22, 23, 24, 27, 25, 26, 29, 31, 28, 30, 94, 95, 92, 93,
+      72, 73, 74, 75, 76, 78, 77, 79, 80, 83, 81, 82, 85, 87, 84, 86, 89, 91, 88, 90,
+      173, 172, 175, 174, 206, 207, 204, 205, 169, 168, 171, 170, 202, 203, 200, 201,
+      117, 116, 119, 118, 142, 143, 140, 141, 114, 112, 115, 113, 137, 139, 136, 138,
+      166, 164, 167, 165, 197, 199, 196, 198, 110, 108, 111, 109, 133, 135, 132, 134,
+      162, 160, 163, 161, 193, 195, 192, 194, 107, 105, 106, 104, 128, 130, 129, 131,
+      159, 157, 158, 156, 188, 190, 189, 191, 99, 98, 97, 96, 120, 121, 122, 123,
+      103, 102, 101, 100, 124, 125, 126, 127, 155, 153, 154, 152, 184, 186, 185, 187,
+      147, 146, 145, 144, 176, 177, 178, 179, 151, 150, 149, 148, 180, 181, 182, 183
+    };
+    for (int iChannel = 0; iChannel < Nchannels; iChannel++) {
+      mChannelCenter[localChannelOrder[iChannel]].SetXYZ(xLocalChannels[iChannel], yLocalChannels[iChannel], zLocalChannels[iChannel]);
+    }
+    
+}