1 | <html> |
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2 | <head> |
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3 | <title>ADG: Geometry</title> |
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4 | </head> |
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5 | |
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6 | <!-- Changed by: Gabriele Cosmo, 18-Apr-2005 --> |
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7 | <!-- $Id: geomAssembly.html,v 1.3 2006/11/23 16:35:55 gcosmo Exp $ --> |
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8 | <!-- $Name: $ --> |
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10 | <table WIDTH="100%"><TR> |
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11 | <td> |
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12 | <a href="../../../../Overview/html/index.html"> |
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13 | <IMG SRC="../../../../resources/html/IconsGIF/Overview.gif" ALT="Overview"></a> |
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14 | <a href="geometry.html"> |
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15 | <IMG SRC="../../../../resources/html/IconsGIF/Contents.gif" ALT="Contents"></a> |
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16 | <a href="geomTouch.html"> |
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20 | </td> |
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21 | <td ALIGN="Right"> |
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22 | <font SIZE="-1" COLOR="#238E23"> |
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23 | <b>Geant4 User's Guide</b> |
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24 | <br> |
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25 | <b>For Application Developers</b> |
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26 | <br> |
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27 | <b>Geometry</b> |
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28 | </font> |
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29 | </td> |
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30 | </tr></table> |
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31 | <br><br> |
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32 | |
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33 | <a name="4.1.6"> |
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34 | <h2>4.1.6 Creating an Assembly of Volumes</h2></a> |
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35 | |
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36 | <p> |
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37 | <tt>G4AssemblyVolume</tt> is a helper class which allows several logical |
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38 | volumes to be combined together in an arbitrary way in 3D space. The result |
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39 | is a placement of a normal logical volume, but where final physical volumes are |
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40 | many. |
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41 | </p> |
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42 | <p> |
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43 | However, an <i>assembly</i> volume does not act as a real mother volume, |
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44 | being an envelope for its daughter volumes. Its role is over at the time |
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45 | the placement of the logical assembly volume is done. The physical volume |
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46 | objects become independent copies of each of the assembled logical volumes. |
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47 | </p> |
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48 | <P> |
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49 | This class is particularly useful when there is a need to create a regular |
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50 | pattern in space of a complex component which consists of different shapes |
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51 | and can't be obtained by using replicated volumes or parametrised volumes |
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52 | (see also figure 4.1.2). |
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53 | Careful usage of <tt>G4AssemblyVolume</tt> must be considered though, in order |
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54 | to avoid cases of "proliferation" of physical volumes all placed in the same |
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55 | mother.</P> |
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56 | <P> |
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57 | <center> |
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58 | <table BORDER=1 CELLPADDING=8> |
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59 | <tr> |
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60 | <td> |
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61 | <IMG SRC="geometry.src/avex1.jpg" ALT="Assembly volumes 1"> |
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62 | <IMG SRC="geometry.src/avex2.jpg" ALT="Assembly volumes 2"> |
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63 | </td> |
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64 | </tr> |
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65 | <tr> |
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66 | <td ALIGN=center> |
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67 | Figure 4.1.2<BR> |
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68 | Examples of <i>assembly</i> of volumes. |
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69 | </td> |
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70 | </tr> |
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71 | </table> |
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72 | </center> |
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73 | <P> |
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74 | |
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75 | <b>Filling an assembly volume with its "daughters"</b> |
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76 | <P> |
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77 | Participating logical volumes are represented as a triplet of <logical |
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78 | volume, translation, rotation> (<tt>G4AssemblyTriplet</tt> class).<BR> |
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79 | The adopted approach is to place each participating logical volume with |
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80 | respect to the assembly's coordinate system, according to the specified |
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81 | translation and rotation. |
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82 | <P> |
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83 | <B>Assembly volume placement</B> |
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84 | <P> |
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85 | An assembly volume object is composed of a set of logical volumes; |
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86 | imprints of it can be made inside a mother logical volume. |
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87 | <P> |
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88 | Since the assembly volume class generates physical volumes during each |
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89 | imprint, the user has no way to specify identifiers for these. An |
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90 | internal counting mechanism is used to compose uniquely the names of the |
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91 | physical volumes created by the invoked <tt>MakeImprint(...)</tt> method(s).<BR> |
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92 | The name for each of the physical volume is generated with the following |
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93 | format: |
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94 | |
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95 | <PRE> |
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96 | av_<B>WWW</B>_impr_<B>XXX</B>_<B>YYY</B>_<B>ZZZ</B> |
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97 | </PRE> |
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98 | |
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99 | where: |
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100 | <UL> |
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101 | <LI><B>WWW</B> - assembly volume instance number</LI> |
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102 | <LI><B>XXX</B> - assembly volume imprint number</LI> |
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103 | <LI><B>YYY</B> - the name of the placed logical volume</LI> |
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104 | <LI><B>ZZZ</B> - the logical volume index inside the assembly volume</LI> |
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105 | </UL> |
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106 | It is however possible to access the constituent physical volumes of an |
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107 | assembly and eventually customise ID and copy-number. |
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108 | |
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109 | <P> |
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110 | <b>Destruction of an assembly volume</b> |
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111 | <P> |
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112 | At destruction all the generated physical volumes and associated rotation |
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113 | matrices of the imprints will be destroyed. A list of physical volumes created |
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114 | by <tt>MakeImprint()</tt> method is kept, in order to be able to cleanup the objects |
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115 | when not needed anymore. This requires the user to keep the assembly objects in |
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116 | memory during the whole job or during the life-time of the <tt>G4Navigator</tt>, |
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117 | logical volume store and physical volume store may keep pointers to physical |
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118 | volumes generated by the assembly volume.<BR> |
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119 | The <tt>MakeImprint()</tt> method will operate correctly also on transformations |
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120 | including reflections and can be applied also to recursive assemblies (i.e., it |
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121 | is possible to generate imprints of assemblies including other assemblies). |
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122 | Giving <TT>true</TT> as the last argument of the <tt>MakeImprint()</tt> method, |
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123 | it is possible to activate the volumes overlap check for the assembly's |
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124 | constituents (the default is <TT>false</TT>).<BR> |
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125 | At destruction of a <tt>G4AssemblyVolume</tt>, all its generated physical |
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126 | volumes and rotation matrices will be freed. |
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127 | <P> |
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128 | <b>Example</b> |
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129 | <P> |
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130 | This example shows how to use the <tt>G4AssemblyVolume</tt> class. |
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131 | It implements a layered detector where each layer consists of 4 plates. |
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132 | <P> |
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133 | In the code below, at first the world volume is defined, then solid |
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134 | and logical volume for the plate are created, followed by the definition of |
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135 | the assembly volume for the layer.<BR> |
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136 | The assembly volume for the layer is then filled by the plates in the same |
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137 | way as normal physical volumes are placed inside a mother volume.<BR> |
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138 | Finally the layers are placed inside the world volume as the imprints |
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139 | of the assembly volume (see source listing 4.1.7). |
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140 | <P> |
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141 | <center> |
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142 | <table BORDER=1 CELLPADDING=8> |
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143 | <tr><td> |
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144 | <pre> |
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145 | static unsigned int layers = 5; |
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146 | |
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147 | void TstVADetectorConstruction::ConstructAssembly() |
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148 | { |
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149 | // Define world volume |
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150 | G4Box* WorldBox = new G4Box( "WBox", worldX/2., worldY/2., worldZ/2. ); |
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151 | G4LogicalVolume* worldLV = new G4LogicalVolume( WorldBox, selectedMaterial, "WLog", 0, 0, 0); |
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152 | G4VPhysicalVolume* worldVol = new G4PVPlacement(0, G4ThreeVector(), "WPhys", worldLV, 0, false, 0); |
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153 | |
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154 | // Define a plate |
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155 | G4Box* PlateBox = new G4Box( "PlateBox", plateX/2., plateY/2., plateZ/2. ); |
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156 | G4LogicalVolume* plateLV = new G4LogicalVolume( PlateBox, Pb, "PlateLV", 0, 0, 0 ); |
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157 | |
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158 | // Define one layer as one assembly volume |
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159 | G4AssemblyVolume* assemblyDetector = new G4AssemblyVolume(); |
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160 | |
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161 | // Rotation and translation of a plate inside the assembly |
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162 | G4RotationMatrix Ra; |
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163 | G4ThreeVector Ta; |
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164 | |
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165 | // Rotation of the assembly inside the world |
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166 | G4RotationMatrix Rm; |
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167 | |
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168 | // Fill the assembly by the plates |
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169 | Ta.setX( caloX/4. ); Ta.setY( caloY/4. ); Ta.setZ( 0. ); |
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170 | assemblyDetector->AddPlacedVolume( plateLV, G4Transform3D(Ta,Ra) ); |
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171 | |
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172 | Ta.setX( -1*caloX/4. ); Ta.setY( caloY/4. ); Ta.setZ( 0. ); |
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173 | assemblyDetector->AddPlacedVolume( plateLV, G4Transform3D(Ta,Ra) ); |
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174 | |
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175 | Ta.setX( -1*caloX/4. ); Ta.setY( -1*caloY/4. ); Ta.setZ( 0. ); |
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176 | assemblyDetector->AddPlacedVolume( plateLV, G4Transform3D(Ta,Ra) ); |
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177 | |
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178 | Ta.setX( caloX/4. ); Ta.setY( -1*caloY/4. ); Ta.setZ( 0. ); |
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179 | assemblyDetector->AddPlacedVolume( plateLV, G4Transform3D(Ta,Ra) ); |
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180 | |
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181 | // Now instantiate the layers |
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182 | for( unsigned int i = 0; i < layers; i++ ) |
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183 | { |
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184 | // Translation of the assembly inside the world |
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185 | G4ThreeVector Tm( 0,0,i*(caloZ + caloCaloOffset) - firstCaloPos ); |
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186 | assemblyDetector->MakeImprint( worldLV, G4Transform3D(Tm,Rm) ); |
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187 | } |
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188 | } |
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189 | </pre> |
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190 | </td></tr> |
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191 | <tr> |
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192 | <td ALIGN=center> |
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193 | Source listing 4.1.7<br> |
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194 | An example of usage of the <tt>G4AssemblyVolume</tt> class. |
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195 | </td> |
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196 | </tr> |
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197 | </table> |
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198 | </center> |
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199 | <p> |
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200 | |
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201 | The resulting detector will look as in figure 4.1.3, below: |
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202 | <P> |
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203 | <center> |
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204 | <table BORDER=1 CELLPADDING=8> |
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205 | <tr> |
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206 | <td><IMG SRC="geometry.src/avpic.jpg" ALT="Assembly volume detector" height=525 width=445></td> |
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207 | <tr> |
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208 | <td ALIGN=center> |
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209 | Figure 4.1.3<br> |
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210 | The geometry corresponding to source listing 4.1.7.</td> |
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211 | </tr> |
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212 | </table> |
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213 | </center> |
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214 | |
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215 | <hr><a href="../../../../Authors/html/subjectsToAuthors.html"> |
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216 | <i>About the authors</a></i> </P> |
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217 | |
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218 | </body> |
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219 | </html> |
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