| 1 | <!-- ******************************************************** -->
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| 2 | <!-- -->
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| 3 | <!-- [History] -->
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| 4 | <!-- Changed by: Katsuya Amako, 30-Nov-1998 -->
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| 5 | <!-- Changed by: Katsuya Amako, 10-Jul-1998 -->
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| 6 | <!-- Proof read by: Joe Chuma, 30-Jun-1999 -->
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| 7 | <!-- Changed by: Takashi SasakI, 15-Nov-2001 -->
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| 8 | <!-- Changed by: Dennis Wright, 27-Nov-2001 -->
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| 9 | <!-- Converted to DocBook: Katsuya Amako, Aug-2006 -->
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| 10 | <!-- Changed by: Hisaya Kurashige, 01-Dec-2007 -->
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| 11 | <!-- -->
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| 12 | <!-- ******************************************************** -->
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| 13 |
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| 14 |
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| 15 | <!-- ******************* Section (Level#1) ****************** -->
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| 16 | <sect1 id="sect.Track">
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| 17 | <title>
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| 18 | Tracking
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| 19 | </title>
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| 20 |
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| 21 | <!-- ******************* Section (Level#2) ****************** -->
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| 22 | <sect2 id="sect.Track.Basic">
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| 23 | <title>
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| 24 | Basic Concepts
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| 25 | </title>
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| 26 |
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| 27 | <!-- ******* Bridgehead ******* -->
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| 28 | <bridgehead renderas='sect4'>
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| 29 | Philosophy of Tracking
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| 30 | </bridgehead>
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| 31 |
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| 32 | <para>
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| 33 | All Geant4 processes, including the transportation of particles,
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| 34 | are treated generically. In spite of the name "<emphasis>tracking</emphasis>",
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| 35 | particles are not <emphasis>transported</emphasis> in the tracking category.
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| 36 | <emphasis>G4TrackingManager</emphasis> is an interface class which brokers
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| 37 | transactions between the event, track and tracking categories. An
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| 38 | instance of this class handles the message passing between the
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| 39 | upper hierarchical object, which is the event manager, and lower
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| 40 | hierarchical objects in the tracking category. The event manager is
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| 41 | a singleton instance of the <emphasis>G4EventManager</emphasis> class.
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| 42 | </para>
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| 43 |
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| 44 | <para>
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| 45 | The tracking manager receives a track from the event manager and
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| 46 | takes the actions required to finish tracking it.
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| 47 | <emphasis>G4TrackingManager</emphasis> aggregates the pointers to
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| 48 | <emphasis>G4SteppingManager,</emphasis> <emphasis>G4Trajectory</emphasis> and
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| 49 | <emphasis>G4UserTrackingAction</emphasis>. Also there is a "use" relation to
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| 50 | <emphasis>G4Track</emphasis> and <emphasis>G4Step</emphasis>.
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| 51 | </para>
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| 52 |
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| 53 | <para>
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| 54 | <emphasis>G4SteppingManager</emphasis> plays an essential role in tracking the
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| 55 | particle. It takes care of all message passing between objects in
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| 56 | the different categories relevant to transporting a particle (for
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| 57 | example, geometry and interactions in matter). Its public method
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| 58 | <literal>Stepping()</literal> steers the stepping of the particle. The
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| 59 | algorithm to handle one step is given below.
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| 60 |
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| 61 | <orderedlist spacing="compact">
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| 62 | <listitem><para>
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| 63 | The particle's velocity at the beginning of the step is
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| 64 | calculated.
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| 65 | </para></listitem>
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| 66 | <listitem><para>
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| 67 | Each active discrete or continuous process must propose a step
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| 68 | length based on the interaction it describes. The smallest of these
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| 69 | step lengths is taken.
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| 70 | </para></listitem>
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| 71 | <listitem><para>
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| 72 | The geometry navigator calculates "Safety", the distance to the
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| 73 | next volume boundary. If the minimum physical-step-length from the
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| 74 | processes is shorter than "Safety", the physical-step-length is
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| 75 | selected as the next step length. In this case, no further
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| 76 | geometrical calculations will be performed.
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| 77 | </para></listitem>
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| 78 | <listitem><para>
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| 79 | If the minimum physical-step-length from the processes is
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| 80 | longer than "Safety", the distance to the next boundary is
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| 81 | re-calculated.
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| 82 | </para></listitem>
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| 83 | <listitem><para>
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| 84 | The smaller of the minimum physical-step-length and the
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| 85 | geometric step length is taken.
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| 86 | </para></listitem>
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| 87 | <listitem><para>
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| 88 | All active continuous processes are invoked. Note that the
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| 89 | particle's kinetic energy will be updated only after all invoked
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| 90 | processes have completed. The change in kinetic energy will be the
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| 91 | sum of the contributions from these processes.
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| 92 | </para></listitem>
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| 93 | <listitem><para>
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| 94 | The track is checked to see whether or not it has been
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| 95 | terminated by a continuous process.
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| 96 | </para></listitem>
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| 97 | <listitem><para>
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| 98 | The current track properties are updated before discrete
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| 99 | processes are invoked. This includes:
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| 100 |
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| 101 | <itemizedlist spacing="compact">
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| 102 | <listitem><para>
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| 103 | updating the kinetic energy of the current track particle (note
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| 104 | that 'sumEnergyChange' is the sum of the new kinetic energy after
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| 105 | each continuos process was invoked, and NOT the sum of the energy
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| 106 | difference before and after the process invocation) and
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| 107 | </para></listitem>
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| 108 | <listitem><para>
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| 109 | updating position and time.
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| 110 | </para></listitem>
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| 111 | </itemizedlist>
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| 112 | </para></listitem>
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| 113 | <listitem><para>
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| 114 | The discrete process is invoked. After the invocation,
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| 115 |
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| 116 | <itemizedlist spacing="compact">
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| 117 | <listitem><para>
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| 118 | the energy of the current track particle is updated, and
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| 119 | </para></listitem>
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| 120 | <listitem><para>
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| 121 | the secondaries from ParticleChange are stored in
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| 122 | SecondaryList. This includes constructing "G4Track" objects, and
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| 123 | setting their member data. Note that the stepping manager is
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| 124 | responsible for deleting secodaries from ParticleChange.
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| 125 | </para></listitem>
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| 126 | </itemizedlist>
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| 127 | </para></listitem>
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| 128 | <listitem><para>
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| 129 | The track is checked to see whether or not it has been
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| 130 | terminated by the discrete process.
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| 131 | </para></listitem>
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| 132 | <listitem><para>
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| 133 | "Safety" is updated.
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| 134 | </para></listitem>
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| 135 | <listitem><para>
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| 136 | If the step was limited by the volume boundary, push the
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| 137 | particle into the next volume.
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| 138 | </para></listitem>
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| 139 | <listitem><para>
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| 140 | Invoke the user intervention <emphasis>G4UserSteppingAction</emphasis>.
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| 141 | </para></listitem>
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| 142 | <listitem><para>
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| 143 | Handle hit information.
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| 144 | </para></listitem>
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| 145 | <listitem><para>
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| 146 | Save data to Trajectory.
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| 147 | </para></listitem>
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| 148 | <listitem><para>
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| 149 | Update the mean free paths of the discrete processes.
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| 150 | </para></listitem>
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| 151 | <listitem><para>
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| 152 | If the parent particle is still alive, reset the maximum
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| 153 | interaction length of the discrete process which has occurred.
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| 154 | </para></listitem>
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| 155 | <listitem><para>
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| 156 | One step completed.
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| 157 | </para></listitem>
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| 158 | </orderedlist>
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| 159 | </para>
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| 160 |
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| 161 | <!-- ******* Bridgehead ******* -->
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| 162 | <bridgehead renderas='sect4'>
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| 163 | What is a Step?
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| 164 | </bridgehead>
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| 165 |
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| 166 | <para>
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| 167 | <emphasis>G4Step</emphasis> stores the transient information of a step. This
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| 168 | includes the two endpoints of the step, <literal>PreStepPoint</literal> and
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| 169 | <literal>PostStepPoint</literal>, which contain the points' coordinates and
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| 170 | the volumes containing the points. <emphasis>G4Step</emphasis> also stores the
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| 171 | change in track properties between the two points. These
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| 172 | properties, such as energy and momentum, are updated as the various
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| 173 | active processes are invoked.
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| 174 | </para>
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| 175 |
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| 176 | <!-- ******* Bridgehead ******* -->
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| 177 | <bridgehead renderas='sect4'>
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| 178 | What is a Track?
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| 179 | </bridgehead>
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| 180 |
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| 181 | <para>
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| 182 | <emphasis>G4Track</emphasis> keeps information on the final status of the
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| 183 | particle after the completion of one step. This means that
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| 184 | <emphasis>G4Track</emphasis> has information on the previous step while the
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| 185 | <literal>AlongStepDoIt</literal>s are being invoked for the step in progress.
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| 186 | Only after finishing all <literal>AlongStepDoIt</literal>s, will
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| 187 | <emphasis>G4Track</emphasis> have the final information (e.g., the final
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| 188 | position) for the step in progress. Also, <emphasis>G4Track</emphasis> will be
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| 189 | updated after each invocation of a <literal>PostStepDoIt</literal>.
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| 190 | </para>
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| 191 |
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| 192 | </sect2>
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| 193 |
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| 194 |
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| 195 | <!-- ******************* Section (Level#2) ****************** -->
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| 196 | <sect2 id="sect.Track.AccInfo">
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| 197 | <title>
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| 198 | Access to Track and Step Information
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| 199 | </title>
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| 200 |
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| 201 | <!-- ******* Bridgehead ******* -->
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| 202 | <bridgehead renderas='sect4'>
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| 203 | How to Get Track Information
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| 204 | </bridgehead>
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| 205 |
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| 206 | <para>
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| 207 | Track information may be accessed by invoking various
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| 208 | <literal>Get</literal> methods provided in the <emphasis>G4Track</emphasis>
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| 209 | class. For details, see the
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| 210 | <emphasis role="bold">Software Reference Manual</emphasis>.
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| 211 | Typical information available includes:
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| 212 |
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| 213 | <itemizedlist spacing="compact">
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| 214 | <listitem><para>
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| 215 | (x,y,z)
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| 216 | </para></listitem>
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| 217 | <listitem><para>
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| 218 | Global time (time since the event was created)
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| 219 | </para></listitem>
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| 220 | <listitem><para>
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| 221 | Local time (time since the track was created)
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| 222 | </para></listitem>
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| 223 | <listitem><para>
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| 224 | Proper time (time in its rest frame since the track was created )
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| 225 | </para></listitem>
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| 226 | <listitem><para>
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| 227 | Momentum direction ( unit vector )
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| 228 | </para></listitem>
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| 229 | <listitem><para>
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| 230 | Kinetic energy
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| 231 | </para></listitem>
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| 232 | <listitem><para>
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| 233 | Accumulated geometrical track length
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| 234 | </para></listitem>
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| 235 | <listitem><para>
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| 236 | Accumulated true track length
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| 237 | </para></listitem>
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| 238 | <listitem><para>
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| 239 | Pointer to dynamic particle
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| 240 | </para></listitem>
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| 241 | <listitem><para>
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| 242 | Pointer to physical volume
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| 243 | </para></listitem>
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| 244 | <listitem><para>
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| 245 | Track ID number
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| 246 | </para></listitem>
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| 247 | <listitem><para>
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| 248 | Track ID number of the parent
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| 249 | </para></listitem>
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| 250 | <listitem><para>
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| 251 | Current step number
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| 252 | </para></listitem>
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| 253 | <listitem><para>
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| 254 | Track status
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| 255 | </para></listitem>
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| 256 | <listitem><para>
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| 257 | (x,y,z) at the start point (vertex position) of the track
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| 258 | </para></listitem>
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| 259 | <listitem><para>
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| 260 | Momentum direction at the start point (vertex position) of the
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| 261 | track
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| 262 | </para></listitem>
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| 263 | <listitem><para>
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| 264 | Kinetic energy at the start point (vertex position) of the track
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| 265 | </para></listitem>
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| 266 | <listitem><para>
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| 267 | Pinter to the process which created the current track
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| 268 | </para></listitem>
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| 269 | </itemizedlist>
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| 270 | </para>
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| 271 |
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| 272 | <!-- ******* Bridgehead ******* -->
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| 273 | <bridgehead renderas='sect4'>
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| 274 | How to Get Step Information
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| 275 | </bridgehead>
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| 276 |
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| 277 | <para>
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| 278 | Step and step-point information can be retrieved by invoking
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| 279 | various <literal>Get</literal> methods provided in the
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| 280 | <emphasis>G4Step</emphasis>/<emphasis>G4StepPoint</emphasis>
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| 281 | classes. For details, see the
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| 282 | <emphasis role="bold">Software Reference Manual</emphasis>.
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| 283 | </para>
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| 284 |
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| 285 | <para>
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| 286 | Information in <emphasis>G4Step</emphasis>
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| 287 | includes:
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| 288 |
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| 289 | <itemizedlist spacing="compact">
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| 290 | <listitem><para>
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| 291 | Pointers to <literal>PreStep</literal> and
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| 292 | <literal>PostStepPoint</literal>
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| 293 | </para></listitem>
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| 294 | <listitem><para>
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| 295 | Geometrical step length (step length before the correction of
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| 296 | multiple scattering)
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| 297 | </para></listitem>
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| 298 | <listitem><para>
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| 299 | True step length (step length after the correction of multiple
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| 300 | scattering)
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| 301 | </para></listitem>
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| 302 | <listitem><para>
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| 303 | Increment of position and time between <literal>PreStepPoint</literal>
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| 304 | and <literal>PostStepPoint</literal>
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| 305 | </para></listitem>
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| 306 | <listitem><para>
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| 307 | Increment of momentum and energy between <literal>PreStepPoint</literal>
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| 308 | and <literal>PostStepPoint</literal>. (Note: to get the energy deposited in
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| 309 | the step, you cannot use this 'Delta energy'. You have to use
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| 310 | 'Total energy deposit' as below.)
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| 311 | </para></listitem>
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| 312 | <listitem><para>
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| 313 | Pointer to <literal>G4Track</literal>
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| 314 | </para></listitem>
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| 315 | <listitem><para>
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| 316 | Total energy deposited during the step - this is the sum of
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| 317 | <para>
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| 318 | <itemizedlist spacing="compact">
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| 319 | <listitem><para>
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| 320 | the energy deposited by the energy loss process, and
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| 321 | </para></listitem>
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| 322 | <listitem><para>
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| 323 | the energy lost by secondaries which have NOT been generated
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| 324 | because each of their energies was below the cut threshold
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| 325 | </para></listitem>
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| 326 | </itemizedlist>
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| 327 | </para>
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| 328 | </para></listitem>
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| 329 | <listitem><para>
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| 330 | Energy deposited not by ionization during the step
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| 331 | </para></listitem>
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| 332 | </itemizedlist>
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| 333 | </para>
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| 334 |
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| 335 | <para>
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| 336 | Information in <emphasis>G4StepPoint</emphasis>
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| 337 | (<literal>PreStepPoint</literal> and <literal>PostStepPoint</literal>)
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| 338 | includes:
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| 339 |
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| 340 | <itemizedlist spacing="compact">
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| 341 | <listitem><para>
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| 342 | (x, y, z, t)
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| 343 | </para></listitem>
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| 344 | <listitem><para>
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| 345 | (px, py, pz, Ek)
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| 346 | </para></listitem>
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| 347 | <listitem><para>
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| 348 | Momentum direction (unit vector)
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| 349 | </para></listitem>
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| 350 | <listitem><para>
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| 351 | Pointers to physical volumes
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| 352 | </para></listitem>
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| 353 | <listitem><para>
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| 354 | Safety
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| 355 | </para></listitem>
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| 356 | <listitem><para>
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| 357 | Beta, gamma
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| 358 | </para></listitem>
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| 359 | <listitem><para>
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| 360 | Polarization
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| 361 | </para></listitem>
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| 362 | <listitem><para>
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| 363 | Step status
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| 364 | </para></listitem>
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| 365 | <listitem><para>
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| 366 | Pointer to the physics process which defined the current step
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| 367 | and its <literal>DoIt</literal> type
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| 368 | </para></listitem>
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| 369 | <listitem><para>
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| 370 | Pointer to the physics process which defined the previous step
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| 371 | and its <literal>DoIt</literal> type
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| 372 | </para></listitem>
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| 373 | <listitem><para>
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| 374 | Total track length
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| 375 | </para></listitem>
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| 376 | <listitem><para>
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| 377 | Global time (time since the current event began)
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| 378 | </para></listitem>
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| 379 | <listitem><para>
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| 380 | Local time (time since the current track began)
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| 381 | </para></listitem>
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| 382 | <listitem><para>
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| 383 | Proper time
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| 384 | </para></listitem>
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| 385 | </itemizedlist>
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| 386 | </para>
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| 387 |
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| 388 | <!-- ******* Bridgehead ******* -->
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| 389 | <bridgehead renderas='sect4'>
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| 390 | How to Get "particle change"
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| 391 | </bridgehead>
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| 392 |
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| 393 | <para>
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| 394 | Particle change information can be accessed by invoking various
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| 395 | <literal>Get</literal> methods provided in the
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| 396 | <emphasis>G4ParticleChange</emphasis> class.
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| 397 | Typical information available includes (for details, see the
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| 398 | <emphasis role="bold">Software Reference Manual</emphasis>):
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| 399 |
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| 400 | <itemizedlist spacing="compact">
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| 401 | <listitem><para>
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| 402 | final momentum direction of the parent particle
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| 403 | </para></listitem>
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| 404 | <listitem><para>
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| 405 | final kinetic energy of the parent particle
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| 406 | </para></listitem>
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| 407 | <listitem><para>
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| 408 | final position of the parent particle
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| 409 | </para></listitem>
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| 410 | <listitem><para>
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| 411 | final global time of the parent particle
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| 412 | </para></listitem>
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| 413 | <listitem><para>
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| 414 | final proper time of the parent particle
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| 415 | </para></listitem>
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| 416 | <listitem><para>
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| 417 | final polarization of the parent particle
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| 418 | </para></listitem>
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| 419 | <listitem><para>
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| 420 | status of the parent particle (<emphasis>G4TrackStatus</emphasis>)
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| 421 | </para></listitem>
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| 422 | <listitem><para>
|
|---|
| 423 | true step length (this is used by multiple scattering to store
|
|---|
| 424 | the result of the transformation from the geometrical step length
|
|---|
| 425 | to the true step length)
|
|---|
| 426 | </para></listitem>
|
|---|
| 427 | <listitem><para>
|
|---|
| 428 | local energy deposited - this consists of either
|
|---|
| 429 | <para>
|
|---|
| 430 | <itemizedlist spacing="compact">
|
|---|
| 431 | <listitem><para>
|
|---|
| 432 | energy deposited by the energy loss process, or
|
|---|
| 433 | </para></listitem>
|
|---|
| 434 | <listitem><para>
|
|---|
| 435 | the energy lost by secondaries which have NOT been generated
|
|---|
| 436 | because each of their energies was below the cut threshold.
|
|---|
| 437 | </para></listitem>
|
|---|
| 438 | </itemizedlist>
|
|---|
| 439 | </para>
|
|---|
| 440 | </para></listitem>
|
|---|
| 441 | <listitem><para>
|
|---|
| 442 | number of secondaries particles
|
|---|
| 443 | </para></listitem>
|
|---|
| 444 | <listitem><para>
|
|---|
| 445 | list of secondary particles (list of <emphasis>G4Track</emphasis>)
|
|---|
| 446 | </para></listitem>
|
|---|
| 447 | </itemizedlist>
|
|---|
| 448 | </para>
|
|---|
| 449 |
|
|---|
| 450 | </sect2>
|
|---|
| 451 |
|
|---|
| 452 |
|
|---|
| 453 | <!-- ******************* Section (Level#2) ****************** -->
|
|---|
| 454 | <sect2 id="sect.Track.SecPar">
|
|---|
| 455 | <title>
|
|---|
| 456 | Handling of Secondary Particles
|
|---|
| 457 | </title>
|
|---|
| 458 |
|
|---|
| 459 | <para>
|
|---|
| 460 | Secondary particles are passed as <emphasis>G4Track</emphasis>s from a physics
|
|---|
| 461 | process to tracking. <emphasis>G4ParticleChange</emphasis> provides the following
|
|---|
| 462 | four methods for a physics process:
|
|---|
| 463 |
|
|---|
| 464 | <itemizedlist spacing="compact">
|
|---|
| 465 | <listitem><para>
|
|---|
| 466 | <literal>AddSecondary( G4Track* aSecondary )</literal>
|
|---|
| 467 | </para></listitem>
|
|---|
| 468 | <listitem><para>
|
|---|
| 469 | <literal>AddSecondary( G4DynamicParticle* aSecondary )</literal>
|
|---|
| 470 | </para></listitem>
|
|---|
| 471 | <listitem><para>
|
|---|
| 472 | <literal>AddSecondary( G4DynamicParticle* aSecondary, G4ThreeVector
|
|---|
| 473 | position )</literal>
|
|---|
| 474 | </para></listitem>
|
|---|
| 475 | <listitem><para>
|
|---|
| 476 | <literal>AddSecondary( G4DynamicParticle* aSecondary, G4double time)</literal>
|
|---|
| 477 | </para></listitem>
|
|---|
| 478 | </itemizedlist>
|
|---|
| 479 | </para>
|
|---|
| 480 |
|
|---|
| 481 | <para>
|
|---|
| 482 | In all but the first, the construction of <emphasis>G4Track</emphasis> is done in
|
|---|
| 483 | the methods using informaton given by the arguments.
|
|---|
| 484 | </para>
|
|---|
| 485 |
|
|---|
| 486 | </sect2>
|
|---|
| 487 |
|
|---|
| 488 |
|
|---|
| 489 | <!-- ******************* Section (Level#2) ****************** -->
|
|---|
| 490 | <sect2 id="sect.Track.UserAct">
|
|---|
| 491 | <title>
|
|---|
| 492 | User Actions
|
|---|
| 493 | </title>
|
|---|
| 494 |
|
|---|
| 495 | <para>
|
|---|
| 496 | There are two classes which allow the user to intervene in the
|
|---|
| 497 | tracking. These are:
|
|---|
| 498 |
|
|---|
| 499 | <itemizedlist spacing="compact">
|
|---|
| 500 | <listitem><para>
|
|---|
| 501 | <emphasis>G4UserTrackingAction</emphasis>, and
|
|---|
| 502 | </para></listitem>
|
|---|
| 503 | <listitem><para>
|
|---|
| 504 | <emphasis>G4UserSteppingAction</emphasis>.
|
|---|
| 505 | </para></listitem>
|
|---|
| 506 | </itemizedlist>
|
|---|
| 507 | </para>
|
|---|
| 508 |
|
|---|
| 509 | <para>
|
|---|
| 510 | Each provides methods which allow the user access to the Geant4
|
|---|
| 511 | kernel at specific points in the tracking. For details, see the
|
|---|
| 512 | <emphasis role="bold">Software Reference Manual</emphasis>.
|
|---|
| 513 | </para>
|
|---|
| 514 |
|
|---|
| 515 | </sect2>
|
|---|
| 516 |
|
|---|
| 517 |
|
|---|
| 518 | <!-- ******************* Section (Level#2) ****************** -->
|
|---|
| 519 | <sect2 id="sect.Track.Verb">
|
|---|
| 520 | <title>
|
|---|
| 521 | Verbose Outputs
|
|---|
| 522 | </title>
|
|---|
| 523 |
|
|---|
| 524 | <para>
|
|---|
| 525 | The verbose information output flag can be turned on or off. The
|
|---|
| 526 | amount of information printed about the track/step, from brief to
|
|---|
| 527 | very detailed, can be controlled by the value of the verbose flag,
|
|---|
| 528 | for example,
|
|---|
| 529 |
|
|---|
| 530 | <informalexample>
|
|---|
| 531 | <programlisting>
|
|---|
| 532 | G4UImanager* UI = G4UImanager::GetUIpointer();
|
|---|
| 533 |
|
|---|
| 534 | UI->ApplyCommand("/tracking/verbose 1");
|
|---|
| 535 | </programlisting>
|
|---|
| 536 | </informalexample>
|
|---|
| 537 | </para>
|
|---|
| 538 |
|
|---|
| 539 | </sect2>
|
|---|
| 540 |
|
|---|
| 541 |
|
|---|
| 542 | <!-- ******************* Section (Level#2) ****************** -->
|
|---|
| 543 | <sect2 id="sect.Track.Traj">
|
|---|
| 544 | <title>
|
|---|
| 545 | Trajectory and Trajectory Point
|
|---|
| 546 | </title>
|
|---|
| 547 |
|
|---|
| 548 | <!-- ******* Bridgehead ******* -->
|
|---|
| 549 | <bridgehead renderas='sect4'>
|
|---|
| 550 | G4Trajectory and G4TrajectoryPoint
|
|---|
| 551 | </bridgehead>
|
|---|
| 552 |
|
|---|
| 553 | <para>
|
|---|
| 554 | <emphasis>G4Trajectory</emphasis> and <emphasis>G4TrajectoryPoint</emphasis>
|
|---|
| 555 | are default concrete classes provided by Geant4, which are derived from the
|
|---|
| 556 | <emphasis>G4VTrajectory</emphasis> and <emphasis>G4VTrajectoryPoint</emphasis>
|
|---|
| 557 | base classes, respectively.
|
|---|
| 558 | A <emphasis>G4Trajectory</emphasis> class object is created by
|
|---|
| 559 | <emphasis>G4TrackingManager</emphasis> when a <emphasis>G4Track</emphasis>
|
|---|
| 560 | is passed from the <emphasis>G4EventManager</emphasis>.
|
|---|
| 561 | <emphasis>G4Trajectory</emphasis> has the following data
|
|---|
| 562 | members:
|
|---|
| 563 |
|
|---|
| 564 | <itemizedlist spacing="compact">
|
|---|
| 565 | <listitem><para>
|
|---|
| 566 | ID numbers of the track and the track's parent
|
|---|
| 567 | </para></listitem>
|
|---|
| 568 | <listitem><para>
|
|---|
| 569 | particle name, charge, and PDG code
|
|---|
| 570 | </para></listitem>
|
|---|
| 571 | <listitem><para>
|
|---|
| 572 | a collection of <emphasis>G4TrajectoryPoint</emphasis> pointers
|
|---|
| 573 | </para></listitem>
|
|---|
| 574 | </itemizedlist>
|
|---|
| 575 | </para>
|
|---|
| 576 |
|
|---|
| 577 | <para>
|
|---|
| 578 | <emphasis>G4TrajectoryPoint</emphasis> corresponds to a step point along
|
|---|
| 579 | the path followed by the track. Its position is given by a
|
|---|
| 580 | <emphasis>G4ThreeVector</emphasis>. A <emphasis>G4TrajectoryPoint</emphasis>
|
|---|
| 581 | class object is created in the <emphasis>AppendStep()</emphasis> method of
|
|---|
| 582 | <emphasis>G4Trajectory</emphasis> and this method is invoked by
|
|---|
| 583 | <emphasis>G4TrackingManager</emphasis> at the end of each step.
|
|---|
| 584 | The first point is created when the <emphasis>G4Trajectory</emphasis>
|
|---|
| 585 | is created, thus the first point is the original vertex.
|
|---|
| 586 | </para>
|
|---|
| 587 |
|
|---|
| 588 | <para>
|
|---|
| 589 | The creation of a trajectory can be controlled by invoking
|
|---|
| 590 | <emphasis>G4TrackingManager::SetStoreTrajectory(G4bool)</emphasis>. The UI
|
|---|
| 591 | command <emphasis>/tracking/storeTrajectory _bool_</emphasis> does the same. The
|
|---|
| 592 | user can set this flag for each individual track from his/her
|
|---|
| 593 | <emphasis>G4UserTrackingAction::PreUserTrackingAction()</emphasis> method.
|
|---|
| 594 | </para>
|
|---|
| 595 |
|
|---|
| 596 | <note><title></title>
|
|---|
| 597 | <para>
|
|---|
| 598 | The user should not create trajectories for secondaries in a shower
|
|---|
| 599 | due to the large amount of memory consumed.
|
|---|
| 600 | </para>
|
|---|
| 601 | </note>
|
|---|
| 602 |
|
|---|
| 603 | <para>
|
|---|
| 604 | All the created trajectories in an event are stored in
|
|---|
| 605 | <emphasis>G4TrajectoryContainer</emphasis> class object and this object will be
|
|---|
| 606 | kept by <emphasis>G4Event</emphasis>. To draw or print trajectories generated in
|
|---|
| 607 | an event, the user may invoke the <emphasis>DrawTrajectory()</emphasis> or
|
|---|
| 608 | <emphasis>ShowTrajectory()</emphasis> methods of <emphasis>G4VTrajectory</emphasis>,
|
|---|
| 609 | respectively, from his/her
|
|---|
| 610 | <emphasis>G4UserEventAction::EndOfEventAction()</emphasis>. The geometry must be
|
|---|
| 611 | drawn before the trajectory drawing. The color of the drawn
|
|---|
| 612 | trajectory depends on the particle charge:
|
|---|
| 613 |
|
|---|
| 614 | <itemizedlist spacing="compact">
|
|---|
| 615 | <listitem><para>
|
|---|
| 616 | negative: red
|
|---|
| 617 | </para></listitem>
|
|---|
| 618 | <listitem><para>
|
|---|
| 619 | neutral: green
|
|---|
| 620 | </para></listitem>
|
|---|
| 621 | <listitem><para>
|
|---|
| 622 | positive: blue
|
|---|
| 623 | </para></listitem>
|
|---|
| 624 | </itemizedlist>
|
|---|
| 625 | </para>
|
|---|
| 626 |
|
|---|
| 627 | <note><title></title>
|
|---|
| 628 | <para>
|
|---|
| 629 | Due to improvements in <emphasis>G4Navigator</emphasis>, a track
|
|---|
| 630 | can execute more than one turn of its spiral trajectory without
|
|---|
| 631 | being broken into smaller steps as long as the trajectory does not
|
|---|
| 632 | cross a geometrical boundary. Thus a drawn trajectory may not be
|
|---|
| 633 | circular.
|
|---|
| 634 | </para>
|
|---|
| 635 | </note>
|
|---|
| 636 |
|
|---|
| 637 | <!-- ******* Bridgehead ******* -->
|
|---|
| 638 | <bridgehead renderas='sect4'>
|
|---|
| 639 | Customizing trajectory and trajectory point
|
|---|
| 640 | </bridgehead>
|
|---|
| 641 |
|
|---|
| 642 | <para>
|
|---|
| 643 | <emphasis>G4Track</emphasis> and <emphasis>G4Step</emphasis> are
|
|---|
| 644 | transient classes; they are not available at the end of the event.
|
|---|
| 645 | Thus, the concrete classes <emphasis>G4VTrajectory</emphasis> and
|
|---|
| 646 | <emphasis>G4VTrajectoryPoint</emphasis> are the only
|
|---|
| 647 | ones a user may employ for end-of-event analysis or for
|
|---|
| 648 | persistency. As mentioned above, the default classes which Geant4
|
|---|
| 649 | provides, i.e. <emphasis>G4Trajectory</emphasis> and
|
|---|
| 650 | <emphasis>G4TrajectoryPoint</emphasis>,
|
|---|
| 651 | have only very primitive quantities. The user can customize his/her
|
|---|
| 652 | own trajectory and trajectory point classes by deriving directly
|
|---|
| 653 | from the respective base classes.
|
|---|
| 654 | </para>
|
|---|
| 655 |
|
|---|
| 656 | <para>
|
|---|
| 657 | To use the customized trajectory, the user must construct a
|
|---|
| 658 | concrete trajectory class object in the
|
|---|
| 659 | <emphasis>G4UserTrackingAction::PreUserTrackingAction()</emphasis> method and
|
|---|
| 660 | make its pointer available to <emphasis>G4TrackingManager</emphasis> by using the
|
|---|
| 661 | <emphasis>SetTrajectory()</emphasis> method. The customized trajectory point
|
|---|
| 662 | class object must be constructed in the <emphasis>AppendStep()</emphasis> method
|
|---|
| 663 | of the user's implementation of the trajectory class. This
|
|---|
| 664 | <emphasis>AppendStep()</emphasis> method will be invoked by
|
|---|
| 665 | <emphasis>G4TrackingManager</emphasis>.
|
|---|
| 666 | </para>
|
|---|
| 667 |
|
|---|
| 668 | <para>
|
|---|
| 669 | To customize trajectory drawing, the user can override the
|
|---|
| 670 | <emphasis>DrawTrajectory()</emphasis> method in his/her own trajectory class.
|
|---|
| 671 | </para>
|
|---|
| 672 |
|
|---|
| 673 | <para>
|
|---|
| 674 | When a customized version of G4Trajectory declares any new class
|
|---|
| 675 | variables, <emphasis>operator new</emphasis> and
|
|---|
| 676 | <emphasis>operator delete</emphasis> must be
|
|---|
| 677 | provided. It is also useful to check that the allocation size in
|
|---|
| 678 | <emphasis>operator new</emphasis> is equal to
|
|---|
| 679 | <emphasis>sizeof(G4Trajectory)</emphasis>. These two points do not
|
|---|
| 680 | apply to <emphasis>G4VTrajectory</emphasis> because it has no
|
|---|
| 681 | <emphasis>operator new</emphasis> or <emphasis>operator delete</emphasis>.
|
|---|
| 682 | </para>
|
|---|
| 683 |
|
|---|
| 684 |
|
|---|
| 685 | </sect2>
|
|---|
| 686 | </sect1>
|
|---|
