From e752b14f44e0762b51e476a3e9158a7cf0ce849b Mon Sep 17 00:00:00 2001
From: Archil Durglishvili <archil.durglishvili@cern.ch>
Date: Sat, 30 Nov 2024 21:27:43 +0100
Subject: [PATCH] Add the method thetaMax() for HCal phi-row segmentation
 needed for SW clustering

---
 .../FCCSWHCalPhiRow_k4geo.h                   |  7 ++++-
 .../src/FCCSWHCalPhiRow_k4geo.cpp             | 27 +++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/detectorSegmentations/include/detectorSegmentations/FCCSWHCalPhiRow_k4geo.h b/detectorSegmentations/include/detectorSegmentations/FCCSWHCalPhiRow_k4geo.h
index acda782e8..1df1353d9 100644
--- a/detectorSegmentations/include/detectorSegmentations/FCCSWHCalPhiRow_k4geo.h
+++ b/detectorSegmentations/include/detectorSegmentations/FCCSWHCalPhiRow_k4geo.h
@@ -111,7 +111,7 @@ namespace dd4hep {
         */
         std::array<double, 2> cellTheta(const CellID& cID) const;
 
-        /**  Get the vector of cell indexes in a give layer.
+        /**  Get the vector of cell indexes in a given layer.
         */
 	inline std::vector<int> cellIndexes(const uint layer) const {
           if(m_radii.empty()) calculateLayerRadii();
@@ -119,6 +119,11 @@ namespace dd4hep {
           else return std::vector<int>();
         }
 
+        /**  Get the thetaMax needed for SW clustering
+        *   return max theta value of the detector
+        */
+        double thetaMax() const;
+
         /**  Get the min and max layer indexes of each HCal part.
         * For Endcap, returns the three elements vector, while for Barrel - single element vector.
         */
diff --git a/detectorSegmentations/src/FCCSWHCalPhiRow_k4geo.cpp b/detectorSegmentations/src/FCCSWHCalPhiRow_k4geo.cpp
index f17059abb..09d644982 100644
--- a/detectorSegmentations/src/FCCSWHCalPhiRow_k4geo.cpp
+++ b/detectorSegmentations/src/FCCSWHCalPhiRow_k4geo.cpp
@@ -602,5 +602,32 @@ std::array<double, 2> FCCSWHCalPhiRow_k4geo::cellTheta(const CellID& cID) const
   return cTheta;
 }
 
+/// determine maximum theta value of the detector. This is used by SW clustering
+double FCCSWHCalPhiRow_k4geo::thetaMax() const {
+  std::vector<std::pair<uint,uint> > minMaxLayerId(getMinMaxLayerId());
+  if(minMaxLayerId.empty()) return 0.;
+
+  // get the first layerId in the Barrel or in the last part of the Endcap
+  uint layer = minMaxLayerId[minMaxLayerId.size()-1].first;
+
+  if(m_radii.empty()) calculateLayerRadii();
+  if(m_cellEdges.empty()) return 0;
+
+  // get the last cell index (which is in the positive-z side)
+  int idx = abs(m_cellIndexes[layer].back());
+
+  // get the z-coordinate of the right-hand edge of the last cell
+  double zhigh = m_cellEdges[layer][idx].second;
+
+  // get the inner radius of the first layer
+  double Rmin = m_radii[layer] - 0.5*m_layerDepth[layer];
+
+  // calculate the minimum theta of the last cell in the first layer -> this is the minimum theta of the detector (Barrel or Endcap)
+  double thetaMin = std::atan2(Rmin,zhigh); // theta min
+
+  return (M_PI - thetaMin); // theta max
+}
+
+
 }
 }