diff -u -r1.7 -r1.8
--- Helix.java	26 Mar 2009 20:58:41 -0000	1.7
+++ Helix.java	27 Mar 2009 19:52:55 -0000	1.8
@@ -9,7 +9,7 @@

  * Helical {@link Trajectory} with its axis parallel to Z.
  *
  * @author D. Onoprienko

- * @version $Id: Helix.java,v 1.7 2009/03/26 20:58:41 onoprien Exp $

+ * @version $Id: Helix.java,v 1.8 2009/03/27 19:52:55 onoprien Exp $

  */
 public class Helix extends AbstractTrajectory {
   

@@ -305,13 +305,12 @@

 
   /** Returns intersection with <tt>ZDisk</tt>. */
   public Intersection intersect(ZDisk zDisk) {

-    double s = findLengthToZ(zDisk._z);

+    double s = findLengthToZ(zDisk.getZ());

     if (Double.isInfinite(s)) return new IntersectionNone(this, zDisk);
     Hep3Vector pos = getPosition(s);

-    double x = pos.x();
-    double y = pos.y();
-    double r2 = x*x + y*y;
-    return (r2 > zDisk._rMin2 && r2 < zDisk._rMax2) ? new IntersectionSingle(s, this, zDisk) : new IntersectionNone(this, zDisk);

+    double r = Math.hypot(pos.x(), pos.y());
+    return (r >= zDisk.getMinRadius() && r <= zDisk.getMaxRadius()) ?
+      new IntersectionSingle(s, this, zDisk) : new IntersectionNone(this, zDisk);

   }
   
   public Intersection intersect(ZCylinder zCylinder) {

diff -u -r1.5 -r1.6
--- Line.java	27 Mar 2009 04:47:38 -0000	1.5
+++ Line.java	27 Mar 2009 19:52:55 -0000	1.6
@@ -8,7 +8,7 @@

  * Straight line {@link Trajectory}.
  *
  * @author D. Onoprienko

- * @version $Id: Line.java,v 1.5 2009/03/27 04:47:38 onoprien Exp $

+ * @version $Id: Line.java,v 1.6 2009/03/27 19:52:55 onoprien Exp $

  */
 public class Line extends AbstractTrajectory {
   

@@ -174,13 +174,12 @@

   }
   
   public Intersection intersect(ZDisk zDisk) {

-    double s = (zDisk._z - _orig.z()) / _dir.z();

+    double s = (zDisk.getZ() - _orig.z()) / _dir.z();

     if (Double.isInfinite(s)) return new IntersectionNone(this, zDisk);
     Hep3Vector pos = getPosition(s);

-    double x = pos.x();
-    double y = pos.y();
-    double r2 = x*x + y*y;
-    return (r2 > zDisk._rMin2 && r2 < zDisk._rMax2) ? new IntersectionSingle(s, this, zDisk) : new IntersectionNone(this, zDisk);

+    double r = Math.hypot(pos.x(), pos.y());
+    return (r >= zDisk.getMinRadius() && r <= zDisk.getMaxRadius()) ?
+      new IntersectionSingle(s, this, zDisk) : new IntersectionNone(this, zDisk);

   }
   
   public Intersection intersect(ZCylinder zCylinder) {

diff -u -r1.2 -r1.3
--- Poca.java	22 Jan 2009 21:01:58 -0000	1.2
+++ Poca.java	27 Mar 2009 19:52:55 -0000	1.3
@@ -9,7 +9,7 @@

  * its constructor.
  *
  * @author D. Onoprienko

- * @version $Id: Poca.java,v 1.2 2009/01/22 21:01:58 onoprien Exp $

+ * @version $Id: Poca.java,v 1.3 2009/03/27 19:52:55 onoprien Exp $

  */
 public class Poca extends AbstractSurface {
   

@@ -55,6 +55,14 @@

       return super.intersect(trajectory);
     }
   }

+
+  /**
+   * Returns the point on this surface that is closest to the specified point.
+   * Implemented to return the point supplied as an argument.
+   */
+  public Hep3Vector project(Hep3Vector point) {
+    return point;
+  }

   
 // -- Private parts :  ---------------------------------------------------------
   

diff -u -r1.2 -r1.3
--- PocaXY.java	22 Jan 2009 21:01:58 -0000	1.2
+++ PocaXY.java	27 Mar 2009 19:52:55 -0000	1.3
@@ -9,7 +9,7 @@

  * point supplied to its constructor.
  *
  * @author D. Onoprienko

- * @version $Id: PocaXY.java,v 1.2 2009/01/22 21:01:58 onoprien Exp $

+ * @version $Id: PocaXY.java,v 1.3 2009/03/27 19:52:55 onoprien Exp $

  */
 public class PocaXY extends AbstractSurface {
   

@@ -56,6 +56,14 @@

     }
   }
 

+  /**
+   * Returns the point on this surface that is closest to the specified point.
+   * Implemented to return the point supplied as an argument.
+   */
+  public Hep3Vector project(Hep3Vector point) {
+    return point;
+  }
+

 // -- Private parts :  ---------------------------------------------------------
   
   private ConstHep3Vector _point;

diff -u -r1.2 -r1.3
--- Surface.java	22 Jan 2009 21:01:58 -0000	1.2
+++ Surface.java	27 Mar 2009 19:52:55 -0000	1.3
@@ -1,16 +1,23 @@

 package org.lcsim.contrib.onoprien.util.swim;
 

+import hep.physics.vec.Hep3Vector;
+

 /**
  * A surface in space.
  *
  * @author D. Onoprienko

- * @version $Id: Surface.java,v 1.2 2009/01/22 21:01:58 onoprien Exp $

+ * @version $Id: Surface.java,v 1.3 2009/03/27 19:52:55 onoprien Exp $

  */
 public interface Surface {
   
   /**
    * Returns intersection of the specified trajectory with this surface.
    */

-  public Intersection intersect(Trajectory trajectory);

+  Intersection intersect(Trajectory trajectory);
+
+  /**
+   * Returns the point on this surface that is closest to the specified point.
+   */
+  Hep3Vector project(Hep3Vector point);

   
 }

diff -u -r1.3 -r1.4
--- ZCylinder.java	26 Mar 2009 20:58:42 -0000	1.3
+++ ZCylinder.java	27 Mar 2009 19:52:55 -0000	1.4
@@ -8,15 +8,15 @@

  * {@link Surface} that represents a bounded cylinder parallel to Z axis.
  *
  * @author D. Onoprienko

- * @version $Id: ZCylinder.java,v 1.3 2009/03/26 20:58:42 onoprien Exp $

+ * @version $Id: ZCylinder.java,v 1.4 2009/03/27 19:52:55 onoprien Exp $

  */
 public class ZCylinder extends AbstractSurface {
 
 // -- Private parts :  ---------------------------------------------------------
 

-  protected ConstHep3Vector _center;
-  protected double _r;
-  protected double _zHalf;

+  private ConstHep3Vector _center;
+  private double _r;
+  private double _zHalf;

   
 // -- Constructors :  ----------------------------------------------------------
 

@@ -98,5 +98,22 @@

       return super.intersect(trajectory);
     }
   }

+
+  /**
+   * Returns the point on this surface that is closest to the specified point.
+   */
+  public Hep3Vector project(Hep3Vector point) {
+    double x = point.x() - _center.x();
+    double y = point.y() - _center.y();
+    double phi = Math.atan2(y, x);
+    double z = point.z();
+    double altZ;
+    if (z > (altZ = _center.z() + _zHalf)) {
+      z = altZ;
+    } else if (z < (altZ = _center.z() - _zHalf)) {
+      z = altZ;
+    }
+    return new ConstHep3Vector(_center.x()+_r*Math.cos(phi), _center.y()+_r*Math.sin(phi), z);
+  }

   
 }

diff -u -r1.2 -r1.3
--- ZDisk.java	22 Jan 2009 21:01:58 -0000	1.2
+++ ZDisk.java	27 Mar 2009 19:52:55 -0000	1.3
@@ -1,19 +1,30 @@

 package org.lcsim.contrib.onoprien.util.swim;
 

+import hep.physics.vec.Hep3Vector;
+
+import org.lcsim.contrib.onoprien.util.ConstHep3Vector;
+

 /**
  * {@link Surface} that represents a disk centered around Z axis and perpendicular to it.
  *
  * @author D. Onoprienko

- * @version $Id: ZDisk.java,v 1.2 2009/01/22 21:01:58 onoprien Exp $

+ * @version $Id: ZDisk.java,v 1.3 2009/03/27 19:52:55 onoprien Exp $

  */
 public class ZDisk extends AbstractSurface {

-  

+
+// -- Private parts :  ---------------------------------------------------------
+
+  private double _z;
+  private double _rMin;
+  private double _rMax;
+
+

 // -- Constructors :  ----------------------------------------------------------
   
   public ZDisk(double z, double radiusMin, double radiusMax) {
     _z = z;

-    _rMin2 = radiusMin * radiusMin;
-    _rMax2 = radiusMax * radiusMax;

+    _rMin = radiusMin;
+    _rMax = radiusMax;

   }
   
 // -- Getters :  ---------------------------------------------------------------

@@ -25,12 +36,12 @@

   
   /** Returns inner radius of this disk. */
   public double getMinRadius() {

-    return Math.sqrt(_rMin2);

+    return _rMin;

   }
   
   /** Returns outer radius of this disk. */
   public double getMaxRadius() {

-    return Math.sqrt(_rMax2);

+    return _rMax;

   }
   
 // -- Implementing Surface :  --------------------------------------------------

@@ -45,9 +56,20 @@

       return super.intersect(trajectory);
     }
   }

-  
-// -- Private parts :  ---------------------------------------------------------
-  
-  double _z;
-  double _rMin2, _rMax2;

+
+  /**
+   * Returns the point on this surface that is closest to the specified point.
+   */
+  public Hep3Vector project(Hep3Vector point) {
+    double r = Math.hypot(point.x(), point.y());
+    if (r > _rMax) {
+      double phi = Math.atan2(point.y(), point.x());
+      return new ConstHep3Vector(_rMax*Math.cos(phi), _rMax*Math.sin(phi), _z);
+    } else if (r < _rMin) {
+      double phi = Math.atan2(point.y(), point.x());
+      return new ConstHep3Vector(_rMin*Math.cos(phi), _rMin*Math.sin(phi), _z);    
+    } else {
+      return new ConstHep3Vector(point.x(), point.y(), _z);
+    }
+  }

 }

diff -u -r1.2 -r1.3
--- ZPlane.java	22 Jan 2009 21:01:58 -0000	1.2
+++ ZPlane.java	27 Mar 2009 19:52:55 -0000	1.3
@@ -1,10 +1,14 @@

 package org.lcsim.contrib.onoprien.util.swim;
 

+import hep.physics.vec.Hep3Vector;
+
+import org.lcsim.contrib.onoprien.util.ConstHep3Vector;
+

 /**
  * {@link Surface} that represents a plane perpendicular to Z axis.
  *
  * @author D. Onoprienko

- * @version $Id: ZPlane.java,v 1.2 2009/01/22 21:01:58 onoprien Exp $

+ * @version $Id: ZPlane.java,v 1.3 2009/03/27 19:52:55 onoprien Exp $

  */
 public class ZPlane extends AbstractSurface {
   

@@ -34,6 +38,13 @@

     }
   }
 

+  /**
+   * Returns the point on this surface that is closest to the specified point.
+   */
+  public Hep3Vector project(Hep3Vector point) {
+    return new ConstHep3Vector(point.x(), point.y(), _z);
+  }
+

 // -- Private parts :  ---------------------------------------------------------
   
   double _z;