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1 README file for the Geant4 BlineTracer module 1 README file for the Geant4 BlineTracer module
2 2
3 Author : Laurent Desorgher (desorgher@phim.uni 3 Author : Laurent Desorgher (desorgher@phim.unibe.ch) - 04/10/2003
4 4
5 -------------------------------- 5 -------------------------------------------------
6 6
7 The BlineTracer module allows to trace and vis 7 The BlineTracer module allows to trace and visualise magnetic field
8 lines in a Geant4 application where particle a 8 lines in a Geant4 application where particle are tracked through the
9 magnetic field (in future, these functionaliti 9 magnetic field (in future, these functionalities may be integrated in
10 the Geant4 kernel). 10 the Geant4 kernel).
11 To use the tracer, the user should copy the cl 11 To use the tracer, the user should copy the classes provided here in
12 his/her own application/example and create som 12 his/her own application/example and create somewhere in his/her code
13 an instance of a G4BlineTracer object. 13 an instance of a G4BlineTracer object.
14 It can be anywhere (for example in the main co 14 It can be anywhere (for example in the main code or in the user class
15 defining the magnetic field): 15 defining the magnetic field):
16 16
17 #include "G4BlineTracer.hh" 17 #include "G4BlineTracer.hh"
18 G4BlineTracer* theBlineTool = new G4BlineTra 18 G4BlineTracer* theBlineTool = new G4BlineTracer();
19 19
20 20
21 Design principles: 21 Design principles:
22 22
23 The core of the tool is the method ComputeBlin 23 The core of the tool is the method ComputeBlines() of G4BlineTracer class.
24 In this method a bline is computed by tracking 24 In this method a bline is computed by tracking a ChargedGeantino in the user
25 defined magnetic field and by using a Bline eq 25 defined magnetic field and by using a Bline equation of motion (class
26 G4BlineEquation, motion along the field) inste 26 G4BlineEquation, motion along the field) instead of a Lorentz equation.
27 27
28 During the execution of this method : 28 During the execution of this method :
29 29
30 -The user defined equations of motion assoc 30 -The user defined equations of motion associated to the different
31 global and local fields are replaced by in 31 global and local fields are replaced by instances of G4BlineEquation
32 associated to the same fields. 32 associated to the same fields.
33 The G4BlineEquation class defines the diffe 33 The G4BlineEquation class defines the differential equation of a
34 magnetic field line. 34 magnetic field line.
35 35
36 -User defined ChordFinders are replaced by n 36 -User defined ChordFinders are replaced by new ChordFinders
37 associated to the G4BlineEquation object. 37 associated to the G4BlineEquation object.
38 38
39 -The user primary generator action, run acti 39 -The user primary generator action, run action, event action and
40 stepping action are replaced by instances o 40 stepping action are replaced by instances of the classes
41 G4BlinePrimaryGeneratorAction, G4BlineTrace 41 G4BlinePrimaryGeneratorAction, G4BlineTracer, G4BlineEventAction
42 and G4BlineSteppingAction respectively. Oth 42 and G4BlineSteppingAction respectively. Other actions are set to
43 a NULL pointer. 43 a NULL pointer.
44 44
45 After the execution of the method, the origina 45 After the execution of the method, the original user defined actions, equation
46 of motions and chord-finders are restored. 46 of motions and chord-finders are restored.
47 47
48 In other words, the deafult run-action is temp 48 In other words, the deafult run-action is temporarly replaced by a
49 G4BlineTracer run-action using the same Geomet 49 G4BlineTracer run-action using the same Geometry, physics and magnetic fields
50 but with a different equation of motion and us 50 but with a different equation of motion and user actions.
51 51
52 The GeneratePrimaries() method of the G4Bline 52 The GeneratePrimaries() method of the G4BlinePrimaryGeneratorAction class
53 call the GeneratePrimaries() method of the use 53 call the GeneratePrimaries() method of the user defined PrimaryGeneratorAction
54 for defining the start position and start time 54 for defining the start position and start time of tracking.
55 Start position for user application and for Bl 55 Start position for user application and for Bline tracking are therefore
56 controlled by the same UI commands. 56 controlled by the same UI commands.
57 The type of particles to be tracked when traci 57 The type of particles to be tracked when tracing Blines is always set
58 to Charged-Geantino. This allows to switch off 58 to Charged-Geantino. This allows to switch off the effect of electromagnetic
59 and hadronics physics when tracing field lines 59 and hadronics physics when tracing field lines.
60 60
61 61
62 The G4BlineEventAction class is responsible to 62 The G4BlineEventAction class is responsible to store computed magnetic field
63 lines as a vector of Polylines and Polymarkers 63 lines as a vector of Polylines and Polymarkers for later visualisation.
64 These vectors can be drawn and reset at any ti 64 These vectors can be drawn and reset at any time.
65 65
66 The stepping action does nothing in this imple 66 The stepping action does nothing in this implementation but it can be used
67 in future versions to limit field line tracing 67 in future versions to limit field line tracing to physical volumes defined
68 by the user. For this purpose a G4BlineStackin 68 by the user. For this purpose a G4BlineStackingAction could also be
69 implemented. 69 implemented.
70 70
71 User Manual: 71 User Manual:
72 72
73 General description: 73 General description:
74 74
75 The BlineTracer is controlled by the UI comman 75 The BlineTracer is controlled by the UI commands contained in the directory
76 /vis/blineTracer. By calling the command 'comp 76 /vis/blineTracer. By calling the command 'computeBline', several magnetic field
77 lines passing through user defined start posit 77 lines passing through user defined start positions are computed.
78 Start positions are generated by the user prim 78 Start positions are generated by the user primary generator action.
79 By doing so, the definition of start positions 79 By doing so, the definition of start positions is the same for usual particles
80 tracking and magnetic field line tracking. 80 tracking and magnetic field line tracking.
81 81
82 A magnetic field line is computed as a track o 82 A magnetic field line is computed as a track of a charged geantino that moves
83 along the field line. The user can define the 83 along the field line. The user can define the maximum length of a tracking step
84 (only valid for Bline tracing purposes) by the 84 (only valid for Bline tracing purposes) by the use of the 'setMaxStepLength'
85 command. 85 command.
86 By using small enough maximum step length, smo 86 By using small enough maximum step length, smooth magnetic field lines are
87 obtained. By using the command 'stockLines' an 87 obtained. By using the command 'stockLines' and 'stockPoints' the user
88 can decide to store the series of tracking ste 88 can decide to store the series of tracking step positions defining
89 a magnetic field line as a Polyline object and 89 a magnetic field line as a Polyline object and/or a PolyMarker object
90 (circles) respectively. 90 (circles) respectively.
91 These objects are stored in vectors of PolyLin 91 These objects are stored in vectors of PolyLines and PolyMarkers.
92 By using the command 'draw', these vectors are 92 By using the command 'draw', these vectors are added to the scene
93 of the visualisation manager, provided that a 93 of the visualisation manager, provided that a scene handler and
94 visualisation driver have been properly create 94 visualisation driver have been properly created.
95 The scene is visualised by invoking the vis co 95 The scene is visualised by invoking the vis command '/vis/show'.
96 Polyline objects are visualised as line segmen 96 Polyline objects are visualised as line segments joining the different
97 step positions defining a line, while for a Po 97 step positions defining a line, while for a Polymarker object markers
98 (here circles), are drawn at each step positi 98 (here circles), are drawn at each step positions.
99 By using the 'setColour' the user defines the 99 By using the 'setColour' the user defines the visualisation colour
100 that will be associated to the next computed m 100 that will be associated to the next computed magnetic field lines.
101 By calling 'setPointSize' the user defines the 101 By calling 'setPointSize' the user defines the size of visualisation markers
102 that will be associated to the next computed 102 that will be associated to the next computed magnetic field lines.
103 The user can remove the vector of Polymarker a 103 The user can remove the vector of Polymarker and Polyline from the memory
104 by invoking 'resetMaterialToBeDrawn'. 104 by invoking 'resetMaterialToBeDrawn'.
105 When using small max step size and polymarkers 105 When using small max step size and polymarkers for visualisation purposes, the
106 thickness of a smooth magnetic field line is o 106 thickness of a smooth magnetic field line is obtained. It is controlled by the
107 Marker size parameter ('setPointSize') 107 Marker size parameter ('setPointSize')
108 108
109 Command description: 109 Command description:
110 /vis/blineTracer/computeBline nb_of_lines : 110 /vis/blineTracer/computeBline nb_of_lines :
111 Parameters: integer nb_of_lines 111 Parameters: integer nb_of_lines
112 Description: Compute nb_of_lines different 112 Description: Compute nb_of_lines different magnetic field lines
113 113
114 /vis/blineTracer/setMaxStepLength max_step_l 114 /vis/blineTracer/setMaxStepLength max_step_length :
115 Parameters: double max_step_length 115 Parameters: double max_step_length
116 Description: Set the maximum tracking step 116 Description: Set the maximum tracking step length for computing
117 magnetic field lines 117 magnetic field lines
118 118
119 /vis/blineTracer/setColour red green 119 /vis/blineTracer/setColour red green blue
120 Parameters: double red, green, blue 120 Parameters: double red, green, blue
121 Description: Define the colour for visual 121 Description: Define the colour for visualisation of the
122 next computed magnetic field lines. 122 next computed magnetic field lines. The color is
123 defined by a RGB code (red,green,bl 123 defined by a RGB code (red,green,blue) with all
124 parameters smaller than 1. 124 parameters smaller than 1.
125 125
126 /vis/blineTracer/stockLines aBool 126 /vis/blineTracer/stockLines aBool
127 Parameters: boolean aBool 127 Parameters: boolean aBool
128 Description: If true the next computed fie 128 Description: If true the next computed field lines are stored
129 as Polylines for further visualisa 129 as Polylines for further visualisation
130 /vis/blineTracer/stockLines aBool 130 /vis/blineTracer/stockLines aBool
131 Parameters: boolean aBool 131 Parameters: boolean aBool
132 Description: If true the next computed fie 132 Description: If true the next computed field lines are stored
133 as Polymarkers for further visuali 133 as Polymarkers for further visualisation
134 134
135 /vis/blineTracer/setPointSize point_size 135 /vis/blineTracer/setPointSize point_size
136 Parameters: double point_size 136 Parameters: double point_size
137 DEscription: set the size of the visualisa 137 DEscription: set the size of the visualisation markers
138 that will be associated with the ne 138 that will be associated with the next computed
139 magnetic field lines 139 magnetic field lines
140 140
141 /vis/blineTracer/resetMaterialToBeDraw 141 /vis/blineTracer/resetMaterialToBeDrawn
142 Parameters: none 142 Parameters: none
143 Description: The vector of Polyline and Po 143 Description: The vector of Polyline and Polymarker representing
144 magnetic field lines to be visualis 144 magnetic field lines to be visualised are removed
145 from memory 145 from memory
146 146
147 /tracking/storeTrajectory 1 : 147 /tracking/storeTrajectory 1 :
148 If the storeTrajectory parameter is n 148 If the storeTrajectory parameter is not set no field lines are
149 stored. 149 stored.
150 150
151 An example for Bline visualisation is provid 151 An example for Bline visualisation is provided in the bline_vis.mac macro.
152 152
153 Current limitations & known problems: 153 Current limitations & known problems:
154 154
155 The tool is working properly only for detect 155 The tool is working properly only for detectors parts where magnetic
156 field are defined. It is planned in th 156 field are defined. It is planned in the future to stop the tracking of
157 field lines in regions where no fields are e 157 field lines in regions where no fields are existing.