correct the calculation of z positions of clusters and docaclusters (#1165)

* correct the calculation of z positions of  clusters and docaclusters

* calculate stereoangle with line information

* remove unused variables

---------

Co-authored-by: Zeyu Zhang <zyzhang@ifarm2401.jlab.org>
Co-authored-by: Zeyu Zhang <zyzhang@ifarm2402.jlab.org>

Author: 3 people

reconstruction/alert/src/main/java/org/jlab/rec/ahdc/Cluster/Cluster.java

@@ -4,17 +4,16 @@
 import org.jlab.rec.ahdc.PreCluster.PreCluster;
 
 import java.util.ArrayList;
+import org.jlab.geom.detector.alert.AHDC.AlertDCFactory;
+import org.jlab.geom.prim.Line3D;
+import org.jlab.geom.prim.Point3D;
 
 /**
  * Cluster are compose by 2 PreCluster on layer with a different stereo angle
  */
 public class Cluster {
 
 	private int                   _trackId = -1;
-	private double                _StereoAngle = 20.0;
-	private double                _DeltaZ = 300.0;
-	private double                _Zoffset = 150.0;
-
 	private double                _Radius;
 	private double                _Phi;
 	private double                _Z;
@@ -26,14 +25,46 @@ public class Cluster {
 	private double                _V;
 	private ArrayList<PreCluster> _PreClusters_list;
 
+	private static Line3D representativeLine(PreCluster pc) {
+		if (pc == null || pc.get_hits_list() == null || pc.get_hits_list().isEmpty()) {
+			return null;
+		}
+		Hit h = pc.get_hits_list().get(0);
+		return h.getLine();
+	}
+	private static double wrapPi(double a) {
+		while (a > Math.PI)  a -= 2.0 * Math.PI;
+		while (a < -Math.PI) a += 2.0 * Math.PI;
+		return a;
+	}
+	private static double stereoTwistFromLine(Line3D line) {
+		if (line == null) {
+			return 0.0;
+		}
+
+		Point3D p0 = line.origin();
+		Point3D p1 = line.end();
+
+		double phi0 = Math.atan2(p0.y(), p0.x());
+		double phi1 = Math.atan2(p1.y(), p1.x());
 
+		return wrapPi(phi1 - phi0);
+	}
 	public Cluster(PreCluster precluster, PreCluster other_precluster) {
 		this._PreClusters_list = new ArrayList<>();
 		_PreClusters_list.add(precluster);
 		_PreClusters_list.add(other_precluster);
 		this._Radius = (precluster.get_Radius() + other_precluster.get_Radius()) / 2;
 
-		this._Z      = ((other_precluster.get_Phi() - precluster.get_Phi()) / (Math.toRadians(_StereoAngle) * Math.pow(-1, precluster.get_Super_layer()-1) - Math.toRadians(_StereoAngle) * Math.pow(-1, other_precluster.get_Super_layer()-1))) * _DeltaZ - _Zoffset;
+		Line3D line1 = representativeLine(precluster);
+		Line3D line2 = representativeLine(other_precluster);
+		Point3D end1 = line1.end();
+		Point3D start1 = line1.origin();
+		double DeltaZ = end1.z()-start1.z();
+		double Zref = end1.z();
+		double StereoAnglep = stereoTwistFromLine(line1);
+		double StereoAngleo = stereoTwistFromLine(line2);
+		this._Z      = ((precluster.get_Phi() - other_precluster.get_Phi()) / (StereoAnglep - StereoAngleo)) * DeltaZ + Zref;
 
 		double x1     = -precluster.get_Radius() * Math.sin(precluster.get_Phi());
 		double y1     = -precluster.get_Radius() * Math.cos(precluster.get_Phi());

reconstruction/alert/src/main/java/org/jlab/rec/ahdc/DocaCluster/DocaClusterRefiner.java

@@ -209,9 +209,10 @@ private static Line3D buildShiftedWireLine(Hit h, Vec2 tangentXY) {
         double dz = e.z() - o.z();
 
         // New origin: (tangent.x, tangent.y, original_z)
-        Point3D oShift = new Point3D(tangentXY.x, tangentXY.y, o.z());
-        Point3D eShift = new Point3D(oShift.x() + dx, oShift.y() + dy, oShift.z() + dz);
-
+        //Point3D oShift = new Point3D(tangentXY.x, tangentXY.y, o.z());
+        //Point3D eShift = new Point3D(oShift.x() + dx, oShift.y() + dy, oShift.z() + dz);
+        Point3D eShift = new Point3D(tangentXY.x, tangentXY.y, e.z());
+        Point3D oShift = new Point3D(tangentXY.x - dx, tangentXY.y - dy, e.z() - dz);
         return new Line3D(oShift, eShift);
     }