diff -u -r1.22 -r1.23
--- TrackUtils.java	25 Aug 2013 21:41:44 -0000	1.22
+++ TrackUtils.java	12 Sep 2013 17:57:54 -0000	1.23
@@ -6,10 +6,12 @@

 import hep.physics.vec.Hep3Matrix;
 import hep.physics.vec.Hep3Vector;
 import hep.physics.vec.VecOp;

+

 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;

+

 import org.lcsim.detector.ITransform3D;
 import org.lcsim.detector.solids.Box;
 import org.lcsim.detector.solids.Point3D;

@@ -28,7 +30,7 @@

 /**
  * 
  * @author Omar Moreno <[log in to unmask]>

- * @version $Id: TrackUtils.java,v 1.22 2013/08/25 21:41:44 phansson Exp $

+ * @version $Id: TrackUtils.java,v 1.23 2013/09/12 17:57:54 phansson Exp $

  * TODO: Switch to JLab coordinates
  */
 

@@ -287,8 +289,71 @@

         }
  
         

+        /**
+         * @param helix input helix object
+         * @param origin of the plane to intercept
+         * @param normal of the plane to intercept
+         * @param eps  criteria on the distance to the plane before stopping iteration
+         * @return position in space at the intercept of the plane
+         */
+        public static Hep3Vector getHelixPlanePositionIter(HelicalTrackFit helix, Hep3Vector origin, Hep3Vector normal, double eps) {
+        	boolean debug = false;
+        	if(debug) {
+        	System.out.printf("--- getHelixPlanePositionIter ---\n");
+        	System.out.printf("Target origin [%.10f %.10f %.10f] normal [%.10f %.10f %.10f]\n",origin.x(),origin.y(),origin.z(),normal.x(),normal.y(),normal.z());
+        	System.out.printf("%.10f %.10f %.10f %.10f %.10f\n",helix.dca(),helix.z0(),helix.phi0(),helix.slope(),helix.R());
+        	}
+        	double x = origin.x();
+        	double d = 9999.9;
+        	double dx = 0.0;
+        	int nIter = 0;
+        	Hep3Vector pos = null;
+        	while( Math.abs(d) > eps && nIter < 50) {
+        		// Calculate position on helix at x
+        		pos = getHelixPosAtX(helix, x + dx);
+        		//	 Check if we are on the plane
+        		d =  VecOp.dot(VecOp.sub(pos, origin), normal);
+        		dx += -1.0 * d / 2.0;
+        	    if(debug) System.out.printf("%d d %.10f pos [%.10f %.10f %.10f] dx %.10f\n", nIter, d, pos.x(),pos.y(),pos.z(), dx);
+        	    nIter +=  1;
+        	}
+    	    return pos;
+        }

         
         /*

+         *  Calculates the point on the helix at a given point along the x-axis
+         *  The normal of the plane is in the same x-y plane as the circle.
+         * 
+         * @param helix
+         * @param x point along x-axis 
+         * @return point on helix at x-coordinate
+         * 
+         */
+        private static Hep3Vector getHelixPosAtX(HelicalTrackFit helix, double x) {
+        	//double C = (double)Math.round(helix.curvature()*1000000)/1000000;
+        	//double R = 1.0/C;
+        	double R = helix.R();
+    	    double dca = helix.dca();
+    	    double z0 = helix.z0();
+    	    double phi0 = helix.phi0();
+    	    double slope = helix.slope();    
+        	//System.out.printf("%.10f %.10f %.10f %.10f %.10f\n",dca,z0,phi0,slope,R);
+    	    
+    	    double xc = (R - dca) * Math.sin(phi0);
+    	    double sinPhi = (xc - x)/R;
+    	    double phi_at_x = Math.asin(sinPhi);
+    	    double dphi_at_x = phi_at_x - phi0;
+    	    if (dphi_at_x > Math.PI) dphi_at_x -= 2.0 * Math.PI;
+    	    if (dphi_at_x < -Math.PI) dphi_at_x += 2.0 * Math.PI;
+    	    double s_at_x = -1.0 * dphi_at_x * R;    
+    	    double y = dca * Math.cos(phi0) - R * Math.cos(phi0) + R * Math.cos(phi_at_x);
+    	    double z = z0 + s_at_x * slope;
+    	    BasicHep3Vector pos = new BasicHep3Vector(x,y,z);
+    	    //System.out.printf("pos %s xc %f phi_at_x %f dphi_at_x %f s_at_x %f\n", pos.toString(),xc,phi_at_x,dphi_at_x,s_at_x);
+    	    return pos;
+        }
+        
+		/*

          *  Calculates the point on the helix in the x-y plane at the intercept with plane
          *  The normal of the plane is in the same x-y plane as the circle.
          *