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1<html>
2<head>
3<title>ADG: Geometry</title>
4</head>
5
6<!-- Changed by: Gabriele Cosmo, 18-Apr-2005 -->
7<!-- $Id: geomAssembly.html,v 1.3 2006/11/23 16:35:55 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>
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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="4.1.6">
34<h2>4.1.6 Creating an Assembly of Volumes</h2></a>
35
36<p> 
37<tt>G4AssemblyVolume</tt> is a helper class which allows several logical
38volumes to be combined together in an arbitrary way in 3D space.  The result
39is a placement of a normal logical volume, but where final physical volumes are
40many.
41</p>
42<p>
43However, an <i>assembly</i> volume does not act as a real mother volume,
44being an envelope for its daughter volumes. Its role is over at the time
45the placement of the logical assembly volume is done. The physical volume
46objects become independent copies of each of the assembled logical volumes.
47</p>
48<P>
49 This class is particularly useful when there is a need to create a regular
50 pattern in space of a complex component which consists of different shapes
51 and can't be obtained by using replicated volumes or parametrised volumes
52 (see also figure 4.1.2).
53 Careful usage of <tt>G4AssemblyVolume</tt> must be considered though, in order
54 to avoid cases of "proliferation" of physical volumes all placed in the same
55 mother.</P>
56<P>
57<center>
58<table BORDER=1 CELLPADDING=8>
59 <tr>
60  <td>
61  <IMG SRC="geometry.src/avex1.jpg" ALT="Assembly volumes 1">
62  <IMG SRC="geometry.src/avex2.jpg" ALT="Assembly volumes 2">
63  </td>
64 </tr>
65 <tr>
66  <td ALIGN=center>
67   Figure 4.1.2<BR>
68   Examples of <i>assembly</i> of volumes.
69  </td>
70 </tr>
71 </table>
72</center>
73<P>
74
75<b>Filling an assembly volume with its "daughters"</b>
76<P>
77 Participating logical volumes are represented as a triplet of &lt;logical
78 volume, translation, rotation&gt; (<tt>G4AssemblyTriplet</tt> class).<BR>
79 The adopted approach is to place each participating logical volume with
80 respect to the assembly's coordinate system, according to the specified
81 translation and rotation.
82<P>
83<B>Assembly volume placement</B>
84<P>
85 An assembly volume object is composed of a set of logical volumes;
86 imprints of it can be made inside a mother logical volume.
87<P>
88 Since the assembly volume class generates physical volumes during each
89 imprint, the user has no way to specify identifiers for these. An
90 internal counting mechanism is used to compose uniquely the names of the
91 physical volumes created by the invoked <tt>MakeImprint(...)</tt> method(s).<BR>
92 The name for each of the&nbsp; physical volume is generated with the following
93 format:
94
95<PRE>
96    av_<B>WWW</B>_impr_<B>XXX</B>_<B>YYY</B>_<B>ZZZ</B>
97</PRE>
98
99 where:
100 <UL>
101 <LI><B>WWW</B> - assembly volume instance number</LI>
102 <LI><B>XXX</B> - assembly volume imprint number</LI>
103 <LI><B>YYY</B> - the name of the placed logical volume</LI>
104 <LI><B>ZZZ</B> - the logical volume index inside the assembly volume</LI>
105 </UL>
106 It is however possible to access the constituent physical volumes of an
107 assembly and eventually customise ID and copy-number.
108
109<P>
110<b>Destruction of an assembly volume</b>
111<P>
112 At destruction all the generated physical volumes and associated rotation
113 matrices of the imprints will be destroyed. A list of physical volumes created
114 by <tt>MakeImprint()</tt> method is kept, in order to be able to cleanup the objects
115 when not needed anymore. This requires the user to keep the assembly objects in
116 memory during the whole job or during the life-time of the <tt>G4Navigator</tt>,
117 logical volume store and physical volume store may keep pointers to physical
118 volumes generated by the assembly volume.<BR>
119 The <tt>MakeImprint()</tt> method will operate correctly also on transformations
120 including reflections and can be applied also to recursive assemblies (i.e., it
121 is possible to generate imprints of assemblies including other assemblies).
122 Giving <TT>true</TT> as the last argument of the <tt>MakeImprint()</tt> method,
123 it is possible to activate the volumes overlap check for the assembly's
124 constituents (the default is <TT>false</TT>).<BR>
125 At destruction of a <tt>G4AssemblyVolume</tt>, all its generated physical
126 volumes and rotation matrices will be freed.
127<P>
128<b>Example</b>
129<P>
130 This example shows how to use the <tt>G4AssemblyVolume</tt> class.
131 It implements a layered detector where each layer consists of 4 plates.
132<P>
133 In the code below, at first the world volume is defined, then solid
134 and logical volume for the plate are created, followed by the definition of
135 the assembly volume for the layer.<BR>
136 The assembly volume for the layer is then filled by the plates in the same
137 way as normal physical volumes are placed inside a mother volume.<BR>
138 Finally the layers are placed inside the world volume as the imprints
139 of the assembly volume (see source listing 4.1.7).
140<P>
141<center>
142 <table BORDER=1 CELLPADDING=8>
143 <tr><td>
144 <pre>
145 static unsigned int layers = 5;
146
147 void TstVADetectorConstruction::ConstructAssembly()
148 {
149   // Define world volume
150   G4Box* WorldBox = new G4Box( "WBox", worldX/2., worldY/2., worldZ/2. );
151   G4LogicalVolume*   worldLV  = new G4LogicalVolume( WorldBox, selectedMaterial, "WLog", 0, 0, 0);
152   G4VPhysicalVolume* worldVol = new G4PVPlacement(0, G4ThreeVector(), "WPhys", worldLV, 0, false, 0);
153
154   // Define a plate
155   G4Box* PlateBox = new G4Box( "PlateBox", plateX/2., plateY/2., plateZ/2. );
156   G4LogicalVolume* plateLV = new G4LogicalVolume( PlateBox, Pb, "PlateLV", 0, 0, 0 );
157
158   // Define one layer as one assembly volume
159   G4AssemblyVolume* assemblyDetector = new G4AssemblyVolume();
160
161   // Rotation and translation of a plate inside the assembly
162   G4RotationMatrix Ra;
163   G4ThreeVector Ta;
164
165   // Rotation of the assembly inside the world
166   G4RotationMatrix Rm;
167
168   // Fill the assembly by the plates
169   Ta.setX( caloX/4. ); Ta.setY( caloY/4. ); Ta.setZ( 0. );
170   assemblyDetector->AddPlacedVolume( plateLV, G4Transform3D(Ta,Ra) );
171
172   Ta.setX( -1*caloX/4. ); Ta.setY( caloY/4. ); Ta.setZ( 0. );
173   assemblyDetector->AddPlacedVolume( plateLV, G4Transform3D(Ta,Ra) );
174
175   Ta.setX( -1*caloX/4. ); Ta.setY( -1*caloY/4. ); Ta.setZ( 0. );
176   assemblyDetector->AddPlacedVolume( plateLV, G4Transform3D(Ta,Ra) );
177
178   Ta.setX( caloX/4. ); Ta.setY( -1*caloY/4. ); Ta.setZ( 0. );
179   assemblyDetector->AddPlacedVolume( plateLV, G4Transform3D(Ta,Ra) );
180
181   // Now instantiate the layers
182   for( unsigned int i = 0; i < layers; i++ )
183   {
184     // Translation of the assembly inside the world
185     G4ThreeVector Tm( 0,0,i*(caloZ + caloCaloOffset) - firstCaloPos );
186     assemblyDetector->MakeImprint( worldLV, G4Transform3D(Tm,Rm) );
187   }
188}
189</pre>
190</td></tr>
191 <tr>
192  <td ALIGN=center>
193   Source listing 4.1.7<br>
194   An example of usage of the <tt>G4AssemblyVolume</tt> class.
195  </td>
196 </tr>
197 </table>
198</center>
199<p>
200
201 The resulting detector will look as in figure 4.1.3, below:
202<P>
203 <center>
204  <table BORDER=1 CELLPADDING=8>
205  <tr>
206  <td><IMG SRC="geometry.src/avpic.jpg" ALT="Assembly volume detector" height=525 width=445></td>
207  <tr>
208  <td ALIGN=center>
209  Figure 4.1.3<br>
210  The geometry corresponding to source listing 4.1.7.</td>
211  </tr>
212  </table>
213 </center>
214
215<hr><a href="../../../../Authors/html/subjectsToAuthors.html">
216<i>About the authors</a></i> </P>
217
218</body>
219</html>
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