geometry/transforms/README.md

0001 \page Exampletransforms Example transforms
0002
0003  This example illustrates various ways to place a volume.
0004
0005  There are two G4PVPlacement constructors. One uses a direct rotation matrix,
0006  via G4Transform3D class. The other uses an inverse rotation matrix.
0007  The rotation matrices themselves, direct or inverse, can be explicitely computed
0008  by users, or built with various G4 build-in transformations methods,
0009  like axial rotations.
0010
0011 ## Geometry construction
0012
0013  Two G4Trd volumes (daughters) are placed within a G4Tubs (mother), in such a way
0014  that their z_axis are in the mother xy plane.
0015  To see the picture, run the example in interactive mode.
0016
0017  The various ways of placement are implemented in the DetectorConstruction class
0018  in the following private functions:
0019
0020  - DetectorConstruction::PlaceWithDirectMatrix() \n
0021    This method is using G4PVPlacement with G4Transform3D, which is constructed from a rotation matrix (G4RotationMatrix) and a translation vector (G4ThreeVector). The rotation and translation in this case represent the active transformation: the solid itself is moved by rotating and translating it to bring it into the system of coordinates of the mother volume.\n
0022    The rotation matrix is defined via the daughter frame axes with respect to the mother frame.\n\n
0023
0024  - DetectorConstruction::PlaceWithInverseMatrix() \n
0025    This method is using G4PVPlacement with a rotation matrix (G4RotationMatrix) and a translation vector (G4ThreeVector). The rotation Matrix represents the rotation of the reference frame of the considered volume relatively to its mother volume’s reference frame. The translation Vector represents the translation of the current volume in the reference frame of its mother volume.  \n
0026    If compared to the previous construct, the transformation in this case is generated by specifying the same translation with respect to its mother volume and the inverse of the rotation matrix.  \n
0027    The rotation matrix is defined again via the daughter frame axes with respect to the mother frame. \n\n
0028
0029  - DetectorConstruction::PlaceWithAxialRotations() \n
0030    This method is using G4PVPlacement with G4Transform3D again, but in difference from
0031    PlaceWithDirectMatrix(), the rotation matrix is defined via rotate[X,Y,Z]() member functions of G4RotationMatrix. \n\n
0032
0033  - DetectorConstruction::PlaceWithEulerAngles() \n
0034    This method is using G4PVPlacement with G4Transform3D again, but with the rotation matrix is defined via Euler angles. \n\n
0035
0036  - DetectorConstruction::PlaceWithReflections() \n
0037    In this method, in addition to two positions defined via "PlaceWithAxialRotations" method, two more positions including reflection symmetry are defined.
0038    When reflections are present in geometry, the placements have to be applied
0039    via G4ReflectionFactory::Place() method, where a G4Transform3D with reflection
0040    can be used.
0041
0042  These functions are then called from the DetectorConstruction::Construct() function.
0043  All methods define exactly same geometry except for the placement
0044  with reflection where trapezoids are placed with their symmetry axis
0045  in parallel with z-axis in order to make easier to check reflection
0046  visually.
0047
0048  The method of placement can be selected interactively via the command
0049  (see DetectorMessenger and transforms.in):
0050 ```
0051 /placement/setMethod method
0052    where method = WithDirectMatrix, WithInverseMatrix, WithAxialRotations,
0053                   WithEulerAngles, WithReflections
0054 ```
0055
0056 ## Physics list
0057
0058  PhysicsList.cc defines only geantino and transportation process.
0059
0060 ## Primary generator
0061
0062  Default kinematic is a geantino, at coordinate origin.
0063  Can be changed with particleGun commands.
0064
0065 ## Physics
0066
0067  No physics; only transportation.
0068
0069 ## Visualisation
0070
0071  In interactive mode, visualization manager is set in the main().
0072  Initialisation of the drawing is done via the commands
0073  `/vis/..`` in the macro vis.mac.
0074
0075 ## How to start ?
0076
0077   - Execute transforms in 'interactive mode' with visualization
0078 ```
0079 % ./transforms
0080 ....
0081 Idle>   ---> type your commands. For instance:
0082 Idle> /placement/setMethod WithInverseMatrix
0083 Idle> /control/execute vis.mac
0084 Idle> /tracking/verbose 1
0085 Idle> /run/beamOn 1
0086 Idle> exit
0087 ```
0088  or, simply
0089 ```
0090 Idle> /control/execute rotations.mac
0091 Idle> /control/execute reflections.mac
0092 ```
0093
0094   - Execute transforms in 'batch' mode from macro files
0095 ```
0096 % transforms transforms.in
0097 ```
0098