1 package org.lcsim.util.swim;
2
3 import org.lcsim.spacegeom.SpacePoint;
4 import org.lcsim.spacegeom.SpaceVector;
5
6 import hep.physics.vec.Hep3Vector;
7
8 /**
9 * A particle trajectory (either a Helix or a Line)
10 * @author tonyj
11 * @version $Id: Trajectory.java,v 1.8 2007/08/16 21:46:45 jstrube Exp $
12 */
13 public interface Trajectory
14 {
15 /**
16 * Gets a point after traveling distance alpha from the origin along the trajectory
17 */
18 SpacePoint getPointAtDistance(double alpha);
19 /**
20 * Calculates the distance at which the trajectory first reaches radius R.
21 * Returns Double.NaN if the trajectory does not intercept the cylinder.
22 * In principle there could be multiple solutions, so this method should
23 * always return the minimum <b>positive</b> solution.
24 */
25
26 public double getDistanceToInfiniteCylinder(double r);
27 /**
28 * Calculate the distance along the trajectory to reach a given Z plane.
29 * Note distance may be negative.
30 */
31 public double getDistanceToZPlane(double z);
32
33 /**
34 * Obtain the point of closest approach (POCA)
35 * of the trajectory to a point. The return value is the distance
36 * parameter s, such that getPointAtDistance(s) is the POCA.
37 * @param point Point in space to swim to
38 * @return The length parameter s
39 */
40 // FIXME this should be a point rather than a vector
41 public double getDistanceToPoint(Hep3Vector point);
42
43 /**
44 * Returns the momentum at a given distance from the origin
45 * @param alpha The length along the trajectory from the origin
46 * @return The momentum at the given distance
47 */
48 public SpaceVector getUnitTangentAtLength(double alpha);
49 }