diff -u -r1.6 -r1.7
--- Helix.java	26 Feb 2009 19:01:28 -0000	1.6
+++ Helix.java	26 Mar 2009 20:58:41 -0000	1.7
@@ -9,7 +9,7 @@

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

- * @version $Id: Helix.java,v 1.6 2009/02/26 19:01:28 onoprien Exp $

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

  */
 public class Helix extends AbstractTrajectory {
   

@@ -257,6 +257,8 @@

       return intersect((Poca) surface);
     } else if (surface instanceof PocaXY) {
       return intersect((PocaXY) surface);

+    } else if (surface instanceof ZDisk) {
+      return intersect((ZDisk) surface);

     } else if (surface instanceof ZPlane) {
       return intersect((ZPlane) surface);
     } else if (surface instanceof ZCylinder) {

@@ -288,10 +290,10 @@

     double sin = - (_ro*a2)/a12;
     double s = getLength(sin,cos);
 

-    double nx = _dir.x()/_ro;
-    double ny = _dir.y()/_ro;
-    double x = _orig.x() + nx * sin + ny * (1-cos);
-    double y = _orig.y() + ny * sin - nx * (1-cos);

+//    double nx = _dir.x()/_ro;
+//    double ny = _dir.y()/_ro;
+//    double x = _orig.x() + nx * sin + ny * (1-cos);
+//    double y = _orig.y() + ny * sin - nx * (1-cos);

     return new IntersectionSingle(s, this, poca);
   }
 

@@ -312,12 +314,18 @@

     return (r2 > zDisk._rMin2 && r2 < zDisk._rMax2) ? new IntersectionSingle(s, this, zDisk) : new IntersectionNone(this, zDisk);
   }
   

-  public Intersection intersect(ZCylinder zCylinder) { // FIXME
-    
-    double ro2 = _c*_c;
-    double a1 = 1. - _dir.z()*_dir.z() - _c*(_orig.x()*_dir.y() + _orig.y()*_dir.x());
-    double a2 = _orig.x()*_dir.x() - _orig.y()*_dir.y();
-    double deltaR = _orig.x()*_orig.x() + _orig.y()*_orig.y() - zCylinder._r*zCylinder._r;

+  public Intersection intersect(ZCylinder zCylinder) {
+
+    double r = zCylinder.getRadius();
+    Hep3Vector center = zCylinder.getCenter();
+
+    double deltaX = _orig.x() - center.x();
+    double deltaY = _orig.y() - center.y();
+    double a1 = 1. - _dir.z()*_dir.z() + _ro*(_dir.y()*deltaX-_dir.x()*deltaY);
+    double a2 = _dir.x()*deltaX + _dir.y()*deltaY;
+
+    double deltaR = deltaX*deltaX + deltaY*deltaY - r*r;
+    double ro2 = _ro*_ro;

     double a12 = a1*a1 + ro2*a2*a2;
     double d = 4.*a2*a2 - 4.*deltaR*a1 - ro2*deltaR*deltaR;
     if (d < 0.) return new IntersectionNone(this, zCylinder);

@@ -326,8 +334,8 @@

     double cos1 = 1. - (ro2* (2.*a2*a2 - deltaR*a1 + a2*d) ) / (2.*a12);
     double cos2 = 1. - (ro2* (2.*a2*a2 - deltaR*a1 - a2*d) ) / (2.*a12);
     

-    double sin1 = (- _c* (2.*a1*a2 + ro2*deltaR*a2 + a1*d)) / (2.*a12);
-    double sin2 = (- _c* (2.*a1*a2 + ro2*deltaR*a2 - a1*d)) / (2.*a12);

+    double sin1 = (- _ro* (2.*a1*a2 + ro2*deltaR*a2 + a1*d)) / (2.*a12);
+    double sin2 = (- _ro* (2.*a1*a2 + ro2*deltaR*a2 - a1*d)) / (2.*a12);

     
     double s1 = getLength(sin1, cos1);
     double s2 = getLength(sin2, cos2);

diff -u -r1.3 -r1.4
--- Line.java	17 Mar 2009 16:57:00 -0000	1.3
+++ Line.java	26 Mar 2009 20:58:41 -0000	1.4
@@ -8,7 +8,7 @@

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

- * @version $Id: Line.java,v 1.3 2009/03/17 16:57:00 onoprien Exp $

+ * @version $Id: Line.java,v 1.4 2009/03/26 20:58:41 onoprien Exp $

  */
 public class Line extends AbstractTrajectory {
   

@@ -198,7 +198,7 @@

           good[i] = false;
         } else {
           double z = getPosition(s).z();

-          good[i] = z > zCylinder._zMin && z < zCylinder._zMax;

+          good[i] = z > zCylinder.getMinZ() && z < zCylinder.getMaxZ();

         }
       }
       if (good[0] && good[1]) {

diff -u -r1.2 -r1.3
--- ZCylinder.java	22 Jan 2009 21:01:58 -0000	1.2
+++ ZCylinder.java	26 Mar 2009 20:58:42 -0000	1.3
@@ -1,36 +1,89 @@

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

+import hep.physics.vec.Hep3Vector;
+

 import org.lcsim.contrib.onoprien.util.ConstHep3Vector;
 
 /**

- * {@link Surface} that represents a bounded cylinder parallel to and centered at Z axis.
- * This surface is characterized by radius, low Z bound, and high Z bound.

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

  *
  * @author D. Onoprienko

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

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

  */
 public class ZCylinder extends AbstractSurface {

+
+// -- Private parts :  ---------------------------------------------------------
+
+  protected ConstHep3Vector _center;
+  protected double _r;
+  protected double _zHalf;

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

-  

+
+  /**
+   * Constructs a cylinder centered around Z axis.
+   * @param radius  Cylinder radius.
+   * @param zMin    Lower Z boundary.
+   * @param zMax    Higher Z boundary.
+   */

   public ZCylinder(double radius, double zMin, double zMax) {

+    if (radius <= 0. || zMin >= zMax) throw new IllegalArgumentException();
+    _r = radius;
+    _zHalf = (zMax - zMin) / 2.;
+    double z = (zMax + zMin) / 2.;
+    _center = new ConstHep3Vector(0., 0., z);
+  }
+
+  /**
+   * Constructs a cylinder with a center at the global coordinate system origin.
+   * @param radius  Cylinder radius.
+   * @param zHalf   Half-length in Z.
+   */
+  public ZCylinder(double radius, double zHalf) {
+    if (radius <= 0. || zHalf <= 0.) throw new IllegalArgumentException();
+    _r = radius;
+    _zHalf = zHalf;
+    _center = ConstHep3Vector.V000;
+  }
+
+  /**
+   * Constract a ZCylinder.
+   * @param center  Center of the cylinder.
+   * @param radius  Cylinder radius.
+   * @param zHalf   Half-length in Z.
+   */
+  public ZCylinder(Hep3Vector center, double radius, double zHalf) {
+    if (radius <= 0. || zHalf <= 0.) throw new IllegalArgumentException();
+    _center = (center instanceof ConstHep3Vector) ? (ConstHep3Vector)center : new ConstHep3Vector(center);
+    _r = radius;
+    _zHalf = zHalf;

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

-  

+
+  /** Returns the center point of this cylinder. */
+  public ConstHep3Vector getCenter() {
+    return _center;
+  }
+

   /** Returns radius of this cylinder. */
   public double getRadius() {
     return _r;
   }

+
+  /** Returns half-length of this cylinder. */
+  public double getHalfZ() {
+    return _zHalf;
+  }

   
   /** Returns minimum Z of this cylinder. */
   public double getMinZ() {

-    return _zMin;

+    return _center.z() - _zHalf;

   }
   
   /** Returns minimum Z of this cylinder. */
   public double getMaxZ() {

-    return _zMax;

+    return _center.z() + _zHalf;

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

@@ -46,9 +99,4 @@

     }
   }
   

-// -- Private parts :  ---------------------------------------------------------
-  
-  double _r;
-  double _zMin, _zMax;
-  

 }