diff -N SvtTrackExtrapolator.java
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ SvtTrackExtrapolator.java	12 May 2012 22:21:20 -0000	1.1
@@ -0,0 +1,78 @@

+package org.lcsim.hps.recon.tracking;
+
+//--- org.lcsim ---//
+import hep.physics.vec.BasicHep3Vector;
+import hep.physics.vec.Hep3Vector;
+
+import org.lcsim.recon.tracking.seedtracker.SeedTrack;
+
+public class SvtTrackExtrapolator {
+
+	SeedTrack track;
+	TrackUtils trackUtils;
+	
+	public static final double ECAL_FACE   = 1450;  // mm
+	public static final double DIPOLE_EDGE = 914; // mm
+	
+	/**
+	 * 
+	 */
+	public SvtTrackExtrapolator(){
+		track = null;
+		trackUtils = new TrackUtils();
+	}
+	
+	/**
+	 * 
+	 */
+	public void setTrack(SeedTrack track){
+		this.track = track;
+		trackUtils.setTrack(track);
+	}
+	
+	/**
+	 * 
+	 */
+	public Hep3Vector getTrackPositionAtEcal(){
+		
+		return this.extrapolateTrack(ECAL_FACE);
+	}
+	
+	/**
+	 * 
+	 */
+	public Hep3Vector extrapolateTrack(double x){
+	
+		if(track == null) throw new RuntimeException("Track has not been set!");
+		
+		if(x > DIPOLE_EDGE){
+			double yDipole = trackUtils.getYOnHelixProjection(x);
+			double s = trackUtils.arcLength(DIPOLE_EDGE, yDipole);
+			double zDipole = trackUtils.getZ0() + s*trackUtils.getTanLambda();
+			double phi = trackUtils.getPhi0() - s/trackUtils.getR();
+			
+			double dx = x - DIPOLE_EDGE;
+			double r = dx/(Math.cos(phi)*(1/Math.sqrt(1 + Math.pow(trackUtils.getTanLambda(), 2))));
+			double dy = r*Math.sin(phi)*(1/Math.sqrt(1 + Math.pow(trackUtils.getTanLambda(), 2)));
+			double dz = r*(trackUtils.getTanLambda()/Math.sqrt(1 + Math.pow(trackUtils.getTanLambda(), 2)));
+			
+			double y = yDipole + dy;
+			double z = zDipole + dz;
+			
+			return new BasicHep3Vector(x, y, z);
+			
+		} else if(x < 0){
+			double dx = x - trackUtils.getX0();
+			double r = dx/(Math.cos(trackUtils.getPhi0())*(1/Math.sqrt(1 + Math.pow(trackUtils.getTanLambda(), 2))));
+			double dy = r*Math.sin(trackUtils.getPhi0())*(1/Math.sqrt(1 + Math.pow(trackUtils.getTanLambda(), 2)));
+			double dz = r*(trackUtils.getTanLambda()/Math.sqrt(1 + Math.pow(trackUtils.getTanLambda(), 2)));
+			
+			double y = trackUtils.getY0() + dy;
+			double z = trackUtils.getZ0() + dz;
+			
+			return new BasicHep3Vector(x, y, z);
+			
+		} else throw new RuntimeException(x + " value is invalid! z-coordinate must lie outside dipole volume.");
+		
+	}
+}