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| 8 | </script></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 5.
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| 9 | Tracking and Physics
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| 10 | </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch04s08.html"><img src="AllResources/IconsGIF/prev.gif" alt="Prev"></a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ch05s02.html"><img src="AllResources/IconsGIF/next.gif" alt="Next"></a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="chap.TrackAndPhysics"></a>Chapter 5.
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| 11 | Tracking and Physics
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| 12 | </h2></div></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sect.Track"></a>5.1.
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| 13 | Tracking
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| 14 | </h2></div></div></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.Track.Basic"></a>5.1.1.
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| 15 | Basic Concepts
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| 16 | </h3></div></div></div><h5><a name="id453977"></a>
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| 17 | Philosophy of Tracking
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| 18 | </h5><p>
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| 19 | All Geant4 processes, including the transportation of particles,
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| 20 | are treated generically. In spite of the name "<span class="emphasis"><em>tracking</em></span>",
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| 21 | particles are not <span class="emphasis"><em>transported</em></span> in the tracking category.
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| 22 | <span class="emphasis"><em>G4TrackingManager</em></span> is an interface class which brokers
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| 23 | transactions between the event, track and tracking categories. An
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| 24 | instance of this class handles the message passing between the
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| 25 | upper hierarchical object, which is the event manager, and lower
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| 26 | hierarchical objects in the tracking category. The event manager is
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| 27 | a singleton instance of the <span class="emphasis"><em>G4EventManager</em></span> class.
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| 28 | </p><p>
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| 29 | The tracking manager receives a track from the event manager and
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| 30 | takes the actions required to finish tracking it.
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| 31 | <span class="emphasis"><em>G4TrackingManager</em></span> aggregates the pointers to
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| 32 | <span class="emphasis"><em>G4SteppingManager,</em></span> <span class="emphasis"><em>G4Trajectory</em></span> and
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| 33 | <span class="emphasis"><em>G4UserTrackingAction</em></span>. Also there is a "use" relation to
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| 34 | <span class="emphasis"><em>G4Track</em></span> and <span class="emphasis"><em>G4Step</em></span>.
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| 35 | </p><p>
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| 36 | <span class="emphasis"><em>G4SteppingManager</em></span> plays an essential role in tracking the
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| 37 | particle. It takes care of all message passing between objects in
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| 38 | the different categories relevant to transporting a particle (for
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| 39 | example, geometry and interactions in matter). Its public method
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| 40 | <code class="literal">Stepping()</code> steers the stepping of the particle. The
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| 41 | algorithm to handle one step is given below.
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| 42 |
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| 43 | </p><div class="orderedlist"><ol type="1" compact><li><p>
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| 44 | The particle's velocity at the beginning of the step is
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| 45 | calculated.
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| 46 | </p></li><li><p>
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| 47 | Each active discrete or continuous process must propose a step
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| 48 | length based on the interaction it describes. The smallest of these
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| 49 | step lengths is taken.
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| 50 | </p></li><li><p>
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| 51 | The geometry navigator calculates "Safety", the distance to the
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| 52 | next volume boundary. If the minimum physical-step-length from the
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| 53 | processes is shorter than "Safety", the physical-step-length is
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| 54 | selected as the next step length. In this case, no further
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| 55 | geometrical calculations will be performed.
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| 56 | </p></li><li><p>
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| 57 | If the minimum physical-step-length from the processes is
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| 58 | longer than "Safety", the distance to the next boundary is
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| 59 | re-calculated.
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| 60 | </p></li><li><p>
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| 61 | The smaller of the minimum physical-step-length and the
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| 62 | geometric step length is taken.
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| 63 | </p></li><li><p>
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| 64 | All active continuous processes are invoked. Note that the
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| 65 | particle's kinetic energy will be updated only after all invoked
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| 66 | processes have completed. The change in kinetic energy will be the
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| 67 | sum of the contributions from these processes.
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| 68 | </p></li><li><p>
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| 69 | The track is checked to see whether or not it has been
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| 70 | terminated by a continuous process.
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| 71 | </p></li><li><p>
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| 72 | The current track properties are updated before discrete
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| 73 | processes are invoked. This includes:
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| 74 |
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| 75 | </p><div class="itemizedlist"><ul type="disc" compact><li><p>
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| 76 | updating the kinetic energy of the current track particle (note
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| 77 | that 'sumEnergyChange' is the sum of the new kinetic energy after
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| 78 | each continuos process was invoked, and NOT the sum of the energy
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| 79 | difference before and after the process invocation) and
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| 80 | </p></li><li><p>
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| 81 | updating position and time.
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| 82 | </p></li></ul></div><p>
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| 83 | </p></li><li><p>
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| 84 | The discrete process is invoked. After the invocation,
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| 85 |
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| 86 | </p><div class="itemizedlist"><ul type="disc" compact><li><p>
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| 87 | the energy of the current track particle is updated, and
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| 88 | </p></li><li><p>
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| 89 | the secondaries from ParticleChange are stored in
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| 90 | SecondaryList. This includes constructing "G4Track" objects, and
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| 91 | setting their member data. Note that the stepping manager is
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| 92 | responsible for deleting secodaries from ParticleChange.
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| 93 | </p></li></ul></div><p>
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| 94 | </p></li><li><p>
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| 95 | The track is checked to see whether or not it has been
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| 96 | terminated by the discrete process.
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| 97 | </p></li><li><p>
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| 98 | "Safety" is updated.
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| 99 | </p></li><li><p>
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| 100 | If the step was limited by the volume boundary, push the
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| 101 | particle into the next volume.
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| 102 | </p></li><li><p>
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| 103 | Invoke the user intervention <span class="emphasis"><em>G4UserSteppingAction</em></span>.
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| 104 | </p></li><li><p>
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| 105 | Handle hit information.
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| 106 | </p></li><li><p>
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| 107 | Save data to Trajectory.
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| 108 | </p></li><li><p>
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| 109 | Update the mean free paths of the discrete processes.
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| 110 | </p></li><li><p>
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| 111 | If the parent particle is still alive, reset the maximum
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| 112 | interaction length of the discrete process which has occurred.
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| 113 | </p></li><li><p>
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| 114 | One step completed.
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| 115 | </p></li></ol></div><p>
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| 116 | </p><h5><a name="id454192"></a>
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| 117 | What is a Step?
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| 118 | </h5><p>
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| 119 | <span class="emphasis"><em>G4Step</em></span> stores the transient information of a step. This
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| 120 | includes the two endpoints of the step, <code class="literal">PreStepPoint</code> and
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| 121 | <code class="literal">PostStepPoint</code>, which contain the points' coordinates and
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| 122 | the volumes containing the points. <span class="emphasis"><em>G4Step</em></span> also stores the
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| 123 | change in track properties between the two points. These
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| 124 | properties, such as energy and momentum, are updated as the various
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| 125 | active processes are invoked.
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| 126 | </p><h5><a name="id454225"></a>
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| 127 | What is a Track?
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| 128 | </h5><p>
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| 129 | <span class="emphasis"><em>G4Track</em></span> keeps information on the final status of the
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| 130 | particle after the completion of one step. This means that
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| 131 | <span class="emphasis"><em>G4Track</em></span> has information on the previous step while the
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| 132 | <code class="literal">AlongStepDoIt</code>s are being invoked for the step in progress.
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| 133 | Only after finishing all <code class="literal">AlongStepDoIt</code>s, will
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| 134 | <span class="emphasis"><em>G4Track</em></span> have the final information (e.g., the final
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| 135 | position) for the step in progress. Also, <span class="emphasis"><em>G4Track</em></span> will be
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| 136 | updated after each invocation of a <code class="literal">PostStepDoIt</code>.
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| 137 | </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.Track.AccInfo"></a>5.1.2.
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| 138 | Access to Track and Step Information
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| 139 | </h3></div></div></div><h5><a name="id454286"></a>
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| 140 | How to Get Track Information
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| 141 | </h5><p>
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| 142 | Track information may be accessed by invoking various
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| 143 | <code class="literal">Get</code> methods provided in the <span class="emphasis"><em>G4Track</em></span>
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| 144 | class. For details, see the
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| 145 | <span class="bold"><strong>Software Reference Manual</strong></span>.
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| 146 | Typical information available includes:
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| 147 |
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| 148 | </p><div class="itemizedlist"><ul type="disc" compact><li><p>
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| 149 | (x,y,z)
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| 150 | </p></li><li><p>
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| 151 | Global time (time since the event was created)
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| 152 | </p></li><li><p>
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| 153 | Local time (time since the track was created)
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| 154 | </p></li><li><p>
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| 155 | Proper time (time in its rest frame since the track was created )
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| 156 | </p></li><li><p>
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| 157 | Momentum direction ( unit vector )
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| 158 | </p></li><li><p>
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| 159 | Kinetic energy
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| 160 | </p></li><li><p>
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| 161 | Accumulated geometrical track length
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| 162 | </p></li><li><p>
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| 163 | Accumulated true track length
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| 164 | </p></li><li><p>
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| 165 | Pointer to dynamic particle
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| 166 | </p></li><li><p>
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| 167 | Pointer to physical volume
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| 168 | </p></li><li><p>
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| 169 | Track ID number
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| 170 | </p></li><li><p>
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| 171 | Track ID number of the parent
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| 172 | </p></li><li><p>
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| 173 | Current step number
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| 174 | </p></li><li><p>
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| 175 | Track status
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| 176 | </p></li><li><p>
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| 177 | (x,y,z) at the start point (vertex position) of the track
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| 178 | </p></li><li><p>
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| 179 | Momentum direction at the start point (vertex position) of the
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| 180 | track
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| 181 | </p></li><li><p>
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| 182 | Kinetic energy at the start point (vertex position) of the track
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| 183 | </p></li><li><p>
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| 184 | Pinter to the process which created the current track
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| 185 | </p></li></ul></div><p>
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| 186 | </p><h5><a name="id454406"></a>
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| 187 | How to Get Step Information
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| 188 | </h5><p>
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| 189 | Step and step-point information can be retrieved by invoking
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| 190 | various <code class="literal">Get</code> methods provided in the
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| 191 | <span class="emphasis"><em>G4Step</em></span>/<span class="emphasis"><em>G4StepPoint</em></span>
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| 192 | classes. For details, see the
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| 193 | <span class="bold"><strong>Software Reference Manual</strong></span>.
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| 194 | </p><p>
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| 195 | Information in <span class="emphasis"><em>G4Step</em></span>
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| 196 | includes:
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| 197 |
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| 198 | </p><div class="itemizedlist"><ul type="disc" compact><li><p>
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| 199 | Pointers to <code class="literal">PreStep</code> and
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| 200 | <code class="literal">PostStepPoint</code>
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| 201 | </p></li><li><p>
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| 202 | Geometrical step length (step length before the correction of
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| 203 | multiple scattering)
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| 204 | </p></li><li><p>
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| 205 | True step length (step length after the correction of multiple
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| 206 | scattering)
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| 207 | </p></li><li><p>
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| 208 | Increment of position and time between <code class="literal">PreStepPoint</code>
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| 209 | and <code class="literal">PostStepPoint</code>
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| 210 | </p></li><li><p>
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| 211 | Increment of momentum and energy between <code class="literal">PreStepPoint</code>
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| 212 | and <code class="literal">PostStepPoint</code>. (Note: to get the energy deposited in
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| 213 | the step, you cannot use this 'Delta energy'. You have to use
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| 214 | 'Total energy deposit' as below.)
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| 215 | </p></li><li><p>
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| 216 | Pointer to <code class="literal">G4Track</code>
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| 217 | </p></li><li><p>
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| 218 | Total energy deposited during the step - this is the sum of
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| 219 | </p><p>
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| 220 | </p><div class="itemizedlist"><ul type="circle" compact><li><p>
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| 221 | the energy deposited by the energy loss process, and
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| 222 | </p></li><li><p>
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| 223 | the energy lost by secondaries which have NOT been generated
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| 224 | because each of their energies was below the cut threshold
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| 225 | </p></li></ul></div><p>
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| 226 | </p><p>
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| 227 | </p></li><li><p>
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| 228 | Energy deposited not by ionization during the step
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| 229 | </p></li></ul></div><p>
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| 230 | </p><p>
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| 231 | Information in <span class="emphasis"><em>G4StepPoint</em></span>
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| 232 | (<code class="literal">PreStepPoint</code> and <code class="literal">PostStepPoint</code>)
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| 233 | includes:
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| 234 |
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| 235 | </p><div class="itemizedlist"><ul type="disc" compact><li><p>
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| 236 | (x, y, z, t)
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| 237 | </p></li><li><p>
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| 238 | (px, py, pz, Ek)
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| 239 | </p></li><li><p>
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| 240 | Momentum direction (unit vector)
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| 241 | </p></li><li><p>
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| 242 | Pointers to physical volumes
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| 243 | </p></li><li><p>
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| 244 | Safety
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| 245 | </p></li><li><p>
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| 246 | Beta, gamma
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| 247 | </p></li><li><p>
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| 248 | Polarization
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| 249 | </p></li><li><p>
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| 250 | Step status
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| 251 | </p></li><li><p>
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| 252 | Pointer to the physics process which defined the current step
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| 253 | and its <code class="literal">DoIt</code> type
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| 254 | </p></li><li><p>
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| 255 | Pointer to the physics process which defined the previous step
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| 256 | and its <code class="literal">DoIt</code> type
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| 257 | </p></li><li><p>
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| 258 | Total track length
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| 259 | </p></li><li><p>
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| 260 | Global time (time since the current event began)
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| 261 | </p></li><li><p>
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| 262 | Local time (time since the current track began)
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| 263 | </p></li><li><p>
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| 264 | Proper time
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| 265 | </p></li></ul></div><p>
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| 266 | </p><h5><a name="id454654"></a>
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| 267 | How to Get "particle change"
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| 268 | </h5><p>
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| 269 | Particle change information can be accessed by invoking various
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| 270 | <code class="literal">Get</code> methods provided in the
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| 271 | <span class="emphasis"><em>G4ParticleChange</em></span> class.
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| 272 | Typical information available includes (for details, see the
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| 273 | <span class="bold"><strong>Software Reference Manual</strong></span>):
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| 274 |
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| 275 | </p><div class="itemizedlist"><ul type="disc" compact><li><p>
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| 276 | final momentum direction of the parent particle
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| 277 | </p></li><li><p>
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| 278 | final kinetic energy of the parent particle
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| 279 | </p></li><li><p>
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| 280 | final position of the parent particle
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| 281 | </p></li><li><p>
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| 282 | final global time of the parent particle
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| 283 | </p></li><li><p>
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| 284 | final proper time of the parent particle
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| 285 | </p></li><li><p>
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| 286 | final polarization of the parent particle
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| 287 | </p></li><li><p>
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| 288 | status of the parent particle (<span class="emphasis"><em>G4TrackStatus</em></span>)
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| 289 | </p></li><li><p>
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| 290 | true step length (this is used by multiple scattering to store
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| 291 | the result of the transformation from the geometrical step length
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| 292 | to the true step length)
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| 293 | </p></li><li><p>
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| 294 | local energy deposited - this consists of either
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| 295 | </p><p>
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| 296 | </p><div class="itemizedlist"><ul type="circle" compact><li><p>
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| 297 | energy deposited by the energy loss process, or
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| 298 | </p></li><li><p>
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| 299 | the energy lost by secondaries which have NOT been generated
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| 300 | because each of their energies was below the cut threshold.
|
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| 301 | </p></li></ul></div><p>
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| 302 | </p><p>
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| 303 | </p></li><li><p>
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| 304 | number of secondaries particles
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| 305 | </p></li><li><p>
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| 306 | list of secondary particles (list of <span class="emphasis"><em>G4Track</em></span>)
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| 307 | </p></li></ul></div><p>
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| 308 | </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.Track.SecPar"></a>5.1.3.
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| 309 | Handling of Secondary Particles
|
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| 310 | </h3></div></div></div><p>
|
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| 311 | Secondary particles are passed as <span class="emphasis"><em>G4Track</em></span>s from a physics
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| 312 | process to tracking. <span class="emphasis"><em>G4ParticleChange</em></span> provides the following
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| 313 | four methods for a physics process:
|
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| 314 |
|
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| 315 | </p><div class="itemizedlist"><ul type="disc" compact><li><p>
|
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| 316 | <code class="literal">AddSecondary( G4Track* aSecondary )</code>
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| 317 | </p></li><li><p>
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| 318 | <code class="literal">AddSecondary( G4DynamicParticle* aSecondary )</code>
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| 319 | </p></li><li><p>
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| 320 | <code class="literal">AddSecondary( G4DynamicParticle* aSecondary, G4ThreeVector
|
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| 321 | position )</code>
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| 322 | </p></li><li><p>
|
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| 323 | <code class="literal">AddSecondary( G4DynamicParticle* aSecondary, G4double time)</code>
|
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| 324 | </p></li></ul></div><p>
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| 325 | </p><p>
|
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| 326 | In all but the first, the construction of <span class="emphasis"><em>G4Track</em></span> is done in
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| 327 | the methods using informaton given by the arguments.
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| 328 | </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.Track.UserAct"></a>5.1.4.
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| 329 | User Actions
|
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| 330 | </h3></div></div></div><p>
|
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| 331 | There are two classes which allow the user to intervene in the
|
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| 332 | tracking. These are:
|
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| 333 |
|
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| 334 | </p><div class="itemizedlist"><ul type="disc" compact><li><p>
|
|---|
| 335 | <span class="emphasis"><em>G4UserTrackingAction</em></span>, and
|
|---|
| 336 | </p></li><li><p>
|
|---|
| 337 | <span class="emphasis"><em>G4UserSteppingAction</em></span>.
|
|---|
| 338 | </p></li></ul></div><p>
|
|---|
| 339 | </p><p>
|
|---|
| 340 | Each provides methods which allow the user access to the Geant4
|
|---|
| 341 | kernel at specific points in the tracking. For details, see the
|
|---|
| 342 | <span class="bold"><strong>Software Reference Manual</strong></span>.
|
|---|
| 343 | </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.Track.Verb"></a>5.1.5.
|
|---|
| 344 | Verbose Outputs
|
|---|
| 345 | </h3></div></div></div><p>
|
|---|
| 346 | The verbose information output flag can be turned on or off. The
|
|---|
| 347 | amount of information printed about the track/step, from brief to
|
|---|
| 348 | very detailed, can be controlled by the value of the verbose flag,
|
|---|
| 349 | for example,
|
|---|
| 350 |
|
|---|
| 351 | </p><div class="informalexample"><pre class="programlisting">
|
|---|
| 352 | G4UImanager* UI = G4UImanager::GetUIpointer();
|
|---|
| 353 |
|
|---|
| 354 | UI->ApplyCommand("/tracking/verbose 1");
|
|---|
| 355 | </pre></div><p>
|
|---|
| 356 | </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="sect.Track.Traj"></a>5.1.6.
|
|---|
| 357 | Trajectory and Trajectory Point
|
|---|
| 358 | </h3></div></div></div><h5><a name="id454939"></a>
|
|---|
| 359 | G4Trajectory and G4TrajectoryPoint
|
|---|
| 360 | </h5><p>
|
|---|
| 361 | <span class="emphasis"><em>G4Trajectory</em></span> and <span class="emphasis"><em>G4TrajectoryPoint</em></span>
|
|---|
| 362 | are default concrete classes provided by Geant4, which are derived from the
|
|---|
| 363 | <span class="emphasis"><em>G4VTrajectory</em></span> and <span class="emphasis"><em>G4VTrajectoryPoint</em></span>
|
|---|
| 364 | base classes, respectively.
|
|---|
| 365 | A <span class="emphasis"><em>G4Trajectory</em></span> class object is created by
|
|---|
| 366 | <span class="emphasis"><em>G4TrackingManager</em></span> when a <span class="emphasis"><em>G4Track</em></span>
|
|---|
| 367 | is passed from the <span class="emphasis"><em>G4EventManager</em></span>.
|
|---|
| 368 | <span class="emphasis"><em>G4Trajectory</em></span> has the following data
|
|---|
| 369 | members:
|
|---|
| 370 |
|
|---|
| 371 | </p><div class="itemizedlist"><ul type="disc" compact><li><p>
|
|---|
| 372 | ID numbers of the track and the track's parent
|
|---|
| 373 | </p></li><li><p>
|
|---|
| 374 | particle name, charge, and PDG code
|
|---|
| 375 | </p></li><li><p>
|
|---|
| 376 | a collection of <span class="emphasis"><em>G4TrajectoryPoint</em></span> pointers
|
|---|
| 377 | </p></li></ul></div><p>
|
|---|
| 378 | </p><p>
|
|---|
| 379 | <span class="emphasis"><em>G4TrajectoryPoint</em></span> corresponds to a step point along
|
|---|
| 380 | the path followed by the track. Its position is given by a
|
|---|
| 381 | <span class="emphasis"><em>G4ThreeVector</em></span>. A <span class="emphasis"><em>G4TrajectoryPoint</em></span>
|
|---|
| 382 | class object is created in the <span class="emphasis"><em>AppendStep()</em></span> method of
|
|---|
| 383 | <span class="emphasis"><em>G4Trajectory</em></span> and this method is invoked by
|
|---|
| 384 | <span class="emphasis"><em>G4TrackingManager</em></span> at the end of each step.
|
|---|
| 385 | The first point is created when the <span class="emphasis"><em>G4Trajectory</em></span>
|
|---|
| 386 | is created, thus the first point is the original vertex.
|
|---|
| 387 | </p><p>
|
|---|
| 388 | The creation of a trajectory can be controlled by invoking
|
|---|
| 389 | <span class="emphasis"><em>G4TrackingManager::SetStoreTrajectory(G4bool)</em></span>. The UI
|
|---|
| 390 | command <span class="emphasis"><em>/tracking/storeTrajectory _bool_</em></span> does the same. The
|
|---|
| 391 | user can set this flag for each individual track from his/her
|
|---|
| 392 | <span class="emphasis"><em>G4UserTrackingAction::PreUserTrackingAction()</em></span> method.
|
|---|
| 393 | </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title"></h3><p>
|
|---|
| 394 | The user should not create trajectories for secondaries in a shower
|
|---|
| 395 | due to the large amount of memory consumed.
|
|---|
| 396 | </p></div><p>
|
|---|
| 397 | All the created trajectories in an event are stored in
|
|---|
| 398 | <span class="emphasis"><em>G4TrajectoryContainer</em></span> class object and this object will be
|
|---|
| 399 | kept by <span class="emphasis"><em>G4Event</em></span>. To draw or print trajectories generated in
|
|---|
| 400 | an event, the user may invoke the <span class="emphasis"><em>DrawTrajectory()</em></span> or
|
|---|
| 401 | <span class="emphasis"><em>ShowTrajectory()</em></span> methods of <span class="emphasis"><em>G4VTrajectory</em></span>,
|
|---|
| 402 | respectively, from his/her
|
|---|
| 403 | <span class="emphasis"><em>G4UserEventAction::EndOfEventAction()</em></span>. The geometry must be
|
|---|
| 404 | drawn before the trajectory drawing. The color of the drawn
|
|---|
| 405 | trajectory depends on the particle charge:
|
|---|
| 406 |
|
|---|
| 407 | </p><div class="itemizedlist"><ul type="disc" compact><li><p>
|
|---|
| 408 | negative: red
|
|---|
| 409 | </p></li><li><p>
|
|---|
| 410 | neutral: green
|
|---|
| 411 | </p></li><li><p>
|
|---|
| 412 | positive: blue
|
|---|
| 413 | </p></li></ul></div><p>
|
|---|
| 414 | </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title"></h3><p>
|
|---|
| 415 | Due to improvements in <span class="emphasis"><em>G4Navigator</em></span>, a track
|
|---|
| 416 | can execute more than one turn of its spiral trajectory without
|
|---|
| 417 | being broken into smaller steps as long as the trajectory does not
|
|---|
| 418 | cross a geometrical boundary. Thus a drawn trajectory may not be
|
|---|
| 419 | circular.
|
|---|
| 420 | </p></div><h5><a name="id455124"></a>
|
|---|
| 421 | Customizing trajectory and trajectory point
|
|---|
| 422 | </h5><p>
|
|---|
| 423 | <span class="emphasis"><em>G4Track</em></span> and <span class="emphasis"><em>G4Step</em></span> are
|
|---|
| 424 | transient classes; they are not available at the end of the event.
|
|---|
| 425 | Thus, the concrete classes <span class="emphasis"><em>G4VTrajectory</em></span> and
|
|---|
| 426 | <span class="emphasis"><em>G4VTrajectoryPoint</em></span> are the only
|
|---|
| 427 | ones a user may employ for end-of-event analysis or for
|
|---|
| 428 | persistency. As mentioned above, the default classes which Geant4
|
|---|
| 429 | provides, i.e. <span class="emphasis"><em>G4Trajectory</em></span> and
|
|---|
| 430 | <span class="emphasis"><em>G4TrajectoryPoint</em></span>,
|
|---|
| 431 | have only very primitive quantities. The user can customize his/her
|
|---|
| 432 | own trajectory and trajectory point classes by deriving directly
|
|---|
| 433 | from the respective base classes.
|
|---|
| 434 | </p><p>
|
|---|
| 435 | To use the customized trajectory, the user must construct a
|
|---|
| 436 | concrete trajectory class object in the
|
|---|
| 437 | <span class="emphasis"><em>G4UserTrackingAction::PreUserTrackingAction()</em></span> method and
|
|---|
| 438 | make its pointer available to <span class="emphasis"><em>G4TrackingManager</em></span> by using the
|
|---|
| 439 | <span class="emphasis"><em>SetTrajectory()</em></span> method. The customized trajectory point
|
|---|
| 440 | class object must be constructed in the <span class="emphasis"><em>AppendStep()</em></span> method
|
|---|
| 441 | of the user's implementation of the trajectory class. This
|
|---|
| 442 | <span class="emphasis"><em>AppendStep()</em></span> method will be invoked by
|
|---|
| 443 | <span class="emphasis"><em>G4TrackingManager</em></span>.
|
|---|
| 444 | </p><p>
|
|---|
| 445 | To customize trajectory drawing, the user can override the
|
|---|
| 446 | <span class="emphasis"><em>DrawTrajectory()</em></span> method in his/her own trajectory class.
|
|---|
| 447 | </p><p>
|
|---|
| 448 | When a customized version of G4Trajectory declares any new class
|
|---|
| 449 | variables, <span class="emphasis"><em>operator new</em></span> and
|
|---|
| 450 | <span class="emphasis"><em>operator delete</em></span> must be
|
|---|
| 451 | provided. It is also useful to check that the allocation size in
|
|---|
| 452 | <span class="emphasis"><em>operator new</em></span> is equal to
|
|---|
| 453 | <span class="emphasis"><em>sizeof(G4Trajectory)</em></span>. These two points do not
|
|---|
| 454 | apply to <span class="emphasis"><em>G4VTrajectory</em></span> because it has no
|
|---|
| 455 | <span class="emphasis"><em>operator new</em></span> or <span class="emphasis"><em>operator delete</em></span>.
|
|---|
| 456 | </p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch04s08.html"><img src="AllResources/IconsGIF/prev.gif" alt="Prev"></a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="ch05s02.html"><img src="AllResources/IconsGIF/next.gif" alt="Next"></a></td></tr><tr><td width="40%" align="left" valign="top">4.8.
|
|---|
| 457 | Command-based scoring
|
|---|
| 458 | </td><td width="20%" align="center"><a accesskey="h" href="index.html"><img src="AllResources/IconsGIF/home.gif" alt="Home"></a></td><td width="40%" align="right" valign="top"> 5.2.
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| 459 | Physics Processes
|
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| 460 | </td></tr></table></div></body></html>
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