Gabriele Cosmo
156 lines
6.9 KiB
Plaintext
156 lines
6.9 KiB
Plaintext
README file for the Geant4 BlineTracer module
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Author : Laurent Desorgher (desorgher@phim.unibe.ch) - 04/10/2003
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The BlineTracer module allows to trace and visualise magnetic field
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lines in a Geant4 application where particle are tracked through the
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magnetic field (in future, these functionalities may be integrated in
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the Geant4 kernel).
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To use the tracer, the user should copy the classes provided here in
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his/her own application/example and create somewhere in his/her code
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an instance of a G4BlineTracer object.
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It can be anywhere (for example in the main code or in the user class
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defining the magnetic field):
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#include "G4BlineTracer.hh"
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G4BlineTracer* theBlineTool = new G4BlineTracer();
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Design principles:
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The core of the tool is the method ComputeBlines() of G4BlineTracer class.
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In this method a bline is computed by tracking a ChargedGeantino in the user
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defined magnetic field and by using a Bline equation of motion (class
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G4BlineEquation, motion along the field) instead of a Lorentz equation.
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During the execution of this method :
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-The user defined equations of motion associated to the different
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global and local fields are replaced by instances of G4BlineEquation
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associated to the same fields.
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The G4BlineEquation class defines the differential equation of a
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magnetic field line.
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-User defined ChordFinders are replaced by new ChordFinders
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associated to the G4BlineEquation object.
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-The user primary generator action, run action, event action and
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stepping action are replaced by instances of the classes
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G4BlinePrimaryGeneratorAction, G4BlineTracer, G4BlineEventAction
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and G4BlineSteppingAction respectively. Other actions are set to
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a NULL pointer.
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After the execution of the method, the original user defined actions, equation
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of motions and chord-finders are restored.
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In other words, the deafult run-action is temporarly replaced by a
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G4BlineTracer run-action using the same Geometry, physics and magnetic fields
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but with a different equation of motion and user actions.
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The GeneratePrimaries() method of the G4BlinePrimaryGeneratorAction class
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call the GeneratePrimaries() method of the user defined PrimaryGeneratorAction
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for defining the start position and start time of tracking.
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Start position for user application and for Bline tracking are therefore
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controlled by the same UI commands.
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The type of particles to be tracked when tracing Blines is always set
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to Charged-Geantino. This allows to switch off the effect of electromagnetic
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and hadronics physics when tracing field lines.
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The G4BlineEventAction class is responsible to store computed magnetic field
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lines as a vector of Polylines and Polymarkers for later visualisation.
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These vectors can be drawn and reset at any time.
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The stepping action does nothing in this implementation but it can be used
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in future versions to limit field line tracing to physical volumes defined
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by the user. For this purpose a G4BlineStackingAction could also be
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implemented.
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User Manual:
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General description:
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The BlineTracer is controlled by the UI commands contained in the directory
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/vis/blineTracer. By calling the command 'computeBline', several magnetic field
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lines passing through user defined start positions are computed.
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Start positions are generated by the user primary generator action.
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By doing so, the definition of start positions is the same for usual particles
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tracking and magnetic field line tracking.
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A magnetic field line is computed as a track of a charged geantino that moves
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along the field line. The user can define the maximum length of a tracking step
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(only valid for Bline tracing purposes) by the use of the 'setMaxStepLength'
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command.
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By using small enough maximum step length, smooth magnetic field lines are
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obtained. By using the command 'stockLines' and 'stockPoints' the user
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can decide to store the series of tracking step positions defining
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a magnetic field line as a Polyline object and/or a PolyMarker object
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(circles) respectively.
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These objects are stored in vectors of PolyLines and PolyMarkers.
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By using the command 'draw', these vectors are added to the scene
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of the visualisation manager, provided that a scene handler and
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visualisation driver have been properly created.
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The scene is visualised by invoking the vis command '/vis/show'.
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Polyline objects are visualised as line segments joining the different
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step positions defining a line, while for a Polymarker object markers
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(here circles), are drawn at each step positions.
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By using the 'setColour' the user defines the visualisation colour
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that will be associated to the next computed magnetic field lines.
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By calling 'setPointSize' the user defines the size of visualisation markers
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that will be associated to the next computed magnetic field lines.
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The user can remove the vector of Polymarker and Polyline from the memory
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by invoking 'resetMaterialToBeDrawn'.
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When using small max step size and polymarkers for visualisation purposes, the
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thickness of a smooth magnetic field line is obtained. It is controlled by the
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Marker size parameter ('setPointSize')
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Command description:
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/vis/blineTracer/computeBline nb_of_lines :
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Parameters: integer nb_of_lines
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Description: Compute nb_of_lines different magnetic field lines
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/vis/blineTracer/setMaxStepLength max_step_length :
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Parameters: double max_step_length
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Description: Set the maximum tracking step length for computing
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magnetic field lines
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/vis/blineTracer/setColour red green blue
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Parameters: double red, green, blue
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Description: Define the colour for visualisation of the
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next computed magnetic field lines. The color is
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defined by a RGB code (red,green,blue) with all
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parameters smaller than 1.
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/vis/blineTracer/stockLines aBool
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Parameters: boolean aBool
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Desscription: If true the next computed field lines are stored
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as Polylines for further visualisation
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/vis/blineTracer/stockLines aBool
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Parameters: boolean aBool
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Desscription: If true the next computed field lines are stored
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as Polymarkers for further visualisation
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/vis/blineTracer/setPointSize point_size
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Parameters: double point_size
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DEscription: set the size of the visualisation markers
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that will be associated with the next computed
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magnetic field lines
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/vis/blineTracer/resetMaterialToBeDrawn
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Parameters: none
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Description: The vector of Polyline and Polymarker representing
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magnetic field lines to be visualised are removed
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from memory
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/tracking/storeTrajectory 1 :
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If the storeTrajectory parameter is not set no field lines are
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stored.
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Current limitations & known problems:
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The tool is working properly only for detectors parts where magnetic
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field are defined. It is planned in the future to stop the tracking of
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field lines in regions where no fields are existing.
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