diff -u -r1.5 -r1.6
--- HelixParamCalculator.java	14 Aug 2009 23:28:22 -0000	1.5
+++ HelixParamCalculator.java	5 Sep 2012 00:42:26 -0000	1.6
@@ -8,6 +8,7 @@

 package org.lcsim.fit.helicaltrack;
 
 import hep.physics.vec.BasicHep3Vector;

+import hep.physics.vec.Hep3Vector;

 import org.lcsim.constants.Constants;
 import org.lcsim.event.MCParticle;
 import org.lcsim.event.EventHeader;

@@ -85,6 +86,64 @@

         z0 = mcp.getOriginZ() - arclength * tanL;
     
     }

+    
+    
+    /*
+    *  added 9/3/2012 by mgraham
+    *   calculate the helix parameters given 3-momentum and a point (+ charge and field)  
+   */            
+    public HelixParamCalculator(Hep3Vector momentum, Hep3Vector origin, int charge,double BField)
+    {
+        
+        //Calculate theta, the of the helix projected into an SZ plane, from the z axis
+        double px = momentum.x();
+        double py = momentum.y();
+        double pz = momentum.z();
+        pt = Math.sqrt(px*px + py*py);
+        p = Math.sqrt(pt*pt + pz*pz);
+        double cth = pz / p;
+        theta = Math.acos(cth);
+//        System.out.println("pt = "+pt+"; costh = "+cth);
+       
+        //Calculate Radius of the Helix
+        R = charge* pt / (Constants.fieldConversion * BField);
+        
+        
+        //Slope in the Dz/Ds sense, tanL Calculation
+        tanL = pz / pt;
+
+        //  Azimuthal direction at origin
+        double mcphi = Math.atan2(py, px);
+
+        //Distance of closest approach Calculation
+        double xc   = origin.x() + R * Math.sin(mcphi);
+        double yc   = origin.y() - R * Math.cos(mcphi);
+//        System.out.println("xc = "+xc+"; yc = "+yc);
+        double Rc = Math.sqrt(xc*xc + yc*yc);
+
+            if(charge>0)
+            {
+            mcdca = R - Rc;
+            }
+            else
+            {
+            mcdca = R + Rc;
+            }
+        
+        
+        //azimuthal calculation of the momentum at the DCA, phi0, Calculation
+        mcphi0 = Math.atan2(xc/(R-mcdca), -yc/(R-mcdca));
+            if(mcphi0<0)
+            {
+                mcphi0 += 2*Math.PI;
+            }
+        //z0 Calculation, z position of the particle at dca
+        x0 = -mcdca*Math.sin(mcphi0);
+        y0 = mcdca*Math.cos(mcphi0);
+        arclength  = (((origin.x()-x0)*Math.cos(mcphi0))+((origin.y()-y0)*Math.sin(mcphi0)));
+        z0 =origin.x() - arclength * tanL;
+    
+    }

     /**
      * Calculates the B-Field from event
      * @param mcpc