1 | <html> |
---|
2 | <head> |
---|
3 | <title>ADG: Geometry</title> |
---|
4 | </head> |
---|
5 | |
---|
6 | <!-- Changed by: Gabriele Cosmo, 18-Apr-2005 --> |
---|
7 | <!-- $Id: geomLogical.html,v 1.3 2006/06/09 13:59:15 gcosmo Exp $ --> |
---|
8 | <!-- $Name: $ --> |
---|
9 | <body> |
---|
10 | <table WIDTH="100%"><TR> |
---|
11 | <td> |
---|
12 | <a href="../../../../Overview/html/index.html"> |
---|
13 | <IMG SRC="../../../../resources/html/IconsGIF/Overview.gif" ALT="Overview"></a> |
---|
14 | <a href="geometry.html"> |
---|
15 | <IMG SRC="../../../../resources/html/IconsGIF/Contents.gif" ALT="Contents"></a> |
---|
16 | <a href="geomSolids.html"> |
---|
17 | <IMG SRC="../../../../resources/html/IconsGIF/Previous.gif" ALT="Previous"></a> |
---|
18 | <a href="geomPhysical.html"> |
---|
19 | <IMG SRC="../../../../resources/html/IconsGIF/Next.gif" ALT="Next"></a> |
---|
20 | </td> |
---|
21 | <td ALIGN="Right"> |
---|
22 | <font SIZE="-1" COLOR="#238E23"> |
---|
23 | <b>Geant4 User's Guide</b> |
---|
24 | <br> |
---|
25 | <b>For Application Developers</b> |
---|
26 | <br> |
---|
27 | <b>Geometry</b> |
---|
28 | </font> |
---|
29 | </td> |
---|
30 | </tr></table> |
---|
31 | <br><br> |
---|
32 | |
---|
33 | <a name="4.1.3"> |
---|
34 | <h2>4.1.3 Logical Volumes</h2></a> |
---|
35 | |
---|
36 | <p> |
---|
37 | The Logical Volume manages the information associated with detector elements |
---|
38 | represented by a given Solid and Material, independently from its physical |
---|
39 | position in the detector. |
---|
40 | </p> |
---|
41 | <p> |
---|
42 | A Logical Volume knows which physical volumes are contained within it. It is |
---|
43 | uniquely defined to be their mother volume. A Logical Volume thus represents |
---|
44 | a hierarchy of unpositioned volumes whose positions relative to one another |
---|
45 | are well defined. By creating Physical Volumes, which are placed instances of |
---|
46 | a Logical Volume, this hierarchy or tree can be repeated. |
---|
47 | </p> |
---|
48 | <p> |
---|
49 | A Logical Volume also manages the information relative to the Visualization |
---|
50 | attributes (<a href="../Visualization/attributes.html">Section 8.6</a>) and |
---|
51 | user-defined parameters related to tracking, electro-magnetic field or cuts |
---|
52 | (through the <tt>G4UserLimits</tt> interface). |
---|
53 | </p> |
---|
54 | <p> |
---|
55 | By default, tracking optimization of the geometry (voxelization) is applied |
---|
56 | to the volume hierarchy identified by a logical volume. It is possible to |
---|
57 | change the default behavior by choosing not to apply geometry optimization |
---|
58 | for a given logical volume. This feature does not apply to the case where the |
---|
59 | associated physical volume is a parameterised volume; in this case, |
---|
60 | optimization is always applied. |
---|
61 | |
---|
62 | <pre> |
---|
63 | G4LogicalVolume( G4VSolid* pSolid, |
---|
64 | G4Material* pMaterial, |
---|
65 | const G4String& Name, |
---|
66 | G4FieldManager* pFieldMgr=0, |
---|
67 | G4VSensitiveDetector* pSDetector=0, |
---|
68 | G4UserLimits* pULimits=0, |
---|
69 | G4bool Optimise=true ) |
---|
70 | </pre> |
---|
71 | </p> |
---|
72 | <P> |
---|
73 | The logical volume provides a way to estimate the <I>mass</I> of a tree of |
---|
74 | volumes defining a detector or sub-detector. This can be achieved by calling |
---|
75 | the method: |
---|
76 | <PRE> |
---|
77 | G4double GetMass(G4bool forced=false) |
---|
78 | </PRE> |
---|
79 | The mass of the logical volume tree is computed from the estimated geometrical |
---|
80 | volume of each solid and material associated with the logical volume and its |
---|
81 | daughters. Note that this computation may require a considerable amount of |
---|
82 | time, depending on the complexity of the geometry tree. |
---|
83 | The returned value is cached by default and can be used for successive calls, |
---|
84 | unless recomputation is forced by providing <TT>true</TT> for the boolean |
---|
85 | argument <TT>forced</TT> in input. Computation should be forced if the |
---|
86 | geometry setup has changed after the previous call.</P> |
---|
87 | <P> |
---|
88 | Finally, the Logical Volume manages the information relative to the Envelopes |
---|
89 | hierarchy required for fast Monte Carlo parameterisations |
---|
90 | (<a href="../TrackingAndPhysics/physicsProcess.html#5.2.6">Section 5.2.6</a>).</P> |
---|
91 | |
---|
92 | <P> </P> |
---|
93 | |
---|
94 | <a name="4.1.3.1"> |
---|
95 | <H4>4.1.3.1 Sub-detector Regions</H4></a> |
---|
96 | |
---|
97 | In complex geometry setups, such as those found in large detectors in |
---|
98 | particle physics experiments, it is useful to think of specific Logical |
---|
99 | Volumes as representing parts (sub-detectors) of the entire detector setup |
---|
100 | which perform specific functions. In such setups, the processing speed of |
---|
101 | a real simulation can be increased by assigning specific production |
---|
102 | <i>cuts</i> to each of these detector parts. This allows a more detailed |
---|
103 | simulation to occur only in those regions where it is required. |
---|
104 | <P> |
---|
105 | The concept of detector <i>Region</i> was introduced to address this need. |
---|
106 | Once the final geometry setup of the detector has been defined, a region |
---|
107 | can be specified by constructing it with: |
---|
108 | <PRE> |
---|
109 | G4Region( const G4String& rName ) |
---|
110 | </PRE></P> |
---|
111 | <P> |
---|
112 | where:</P> |
---|
113 | <P> |
---|
114 | <table border=1 cellpadding=8> |
---|
115 | <td><tt>rName</tt> <td>String identifier for the detector region |
---|
116 | </table></P> |
---|
117 | <P> |
---|
118 | A <tt>G4Region</tt> must then be assigned to a logical volume, in order to |
---|
119 | make it a <i>Root Logical Volume</i>: |
---|
120 | <PRE> |
---|
121 | G4Region* emCalorimeter = new G4Region("EM-Calorimeter"); |
---|
122 | emCalorimeter->AddRootLogicalVolume(emCalorimeter); |
---|
123 | </PRE> |
---|
124 | A root logical volume is the first volume at the top of the hierarchy to |
---|
125 | which a given region is assigned. Once the region is assigned to the root |
---|
126 | logical volume, the information is automatically propagated to the volume |
---|
127 | tree, so that each daughter volume shares the same region. Propagation on |
---|
128 | a tree branch will be interrupted if an already existing root logical |
---|
129 | volume is encountered.</P> |
---|
130 | <P> |
---|
131 | A specific <i>Production Cut</i> can be assigned to the region, by defining |
---|
132 | and assigning to it a <tt>G4ProductionCut</tt> object |
---|
133 | <PRE> |
---|
134 | emCalorimeter->SetProductionCuts(emCalCuts); |
---|
135 | </PRE> |
---|
136 | <a href="../TrackingAndPhysics/thresholdVScut.html#5.4.2">Section 5.4.2</a> |
---|
137 | describes how to define a production cut. The same region can be assigned |
---|
138 | to more than one root logical volume, and root logical volumes can be |
---|
139 | removed from an existing region. A logical volume can have only <i>one</i> |
---|
140 | region assigned to it. Regions will be automatically registered in a store |
---|
141 | which will take care of destroying them at the end of the job. A default |
---|
142 | region with a default production cut is automatically created and assigned |
---|
143 | to the world volume.</P> |
---|
144 | |
---|
145 | <hr><a href="../../../../Authors/html/subjectsToAuthors.html"> |
---|
146 | <i>About the authors</a></i> </P> |
---|
147 | |
---|
148 | </body> |
---|
149 | </html> |
---|