| 1 | <html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>FAQ.3. Geometry</title><link rel="stylesheet" href="../xml/XSLCustomizationLayer/G4HTMLStylesheet.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.71.1"><link rel="start" href="index.html" title="Geant4 User's Guide for Application Developers"><link rel="up" href="ch10.html" title="Chapter FAQ. Frequentry Asked Questions"><link rel="prev" href="ch10s02.html" title="FAQ.2. Run Time Problems"><link rel="next" href="ch10s04.html" title="FAQ.4. Tracks and steps"><script language="JavaScript">
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| 2 | function remote_win(fName)
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| 3 | {
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| 4 | var url = "AllResources/Detector/geometry.src/" + fName;
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| 5 | RemoteWin=window.open(url,"","resizable=no,toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=0,copyhistory=0,width=520,height=520")
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| 6 | RemoteWin.creator=self
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| 7 | }
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| 8 | </script></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">FAQ.3.
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| 9 | Geometry
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| 10 | </th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch10s02.html"><img src="AllResources/IconsGIF/prev.gif" alt="Prev"></a> </td><th width="60%" align="center">Chapter FAQ.
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| 11 | Frequentry Asked Questions
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| 12 | </th><td width="20%" align="right"> <a accesskey="n" href="ch10s04.html"><img src="AllResources/IconsGIF/next.gif" alt="Next"></a></td></tr></table><hr></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="qanda.Geometry"></a>FAQ.3.
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| 13 | Geometry
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| 14 | </h2></div></div></div><div class="qandaset"><table border="0" summary="Q and A Set"><col align="left" width="1%"><tbody><tr class="question"><td align="left" valign="top"><a name="qanda.Geometry.GenPnt"></a><a name="id553829"></a><b>Q:</b></td><td align="left" valign="top"><p>
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| 15 | I have a generic point and I would like to know in which physical
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| 16 | volume I'm located in my detector geometry.
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| 17 | </p></td></tr><tr class="answer"><td align="left" valign="top"><b>A:</b></td><td align="left" valign="top"><p>
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| 18 | The best way of doing this is by invoking the G4Navigator. First
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| 19 | get a pointer of the navigator through the G4TransportationManager,
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| 20 | and then locate the point. i.e.
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| 21 | </p><div class="informalexample"><pre class="programlisting">
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| 22 | #include "G4TransportationManager.hh"
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| 23 | #include "G4Navigator.hh"
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| 24 | G4ThreeVector myPoint = ....;
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| 25 | G4Navigator* theNavigator = G4TransportationManager::GetTransportationManager()
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| 26 | ->GetNavigatorForTracking();
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| 27 | G4VPhysicalVolume* myVolume = theNavigator->LocateGlobalPointAndSetup(myPoint);
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| 28 | </pre></div><p>
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| 29 |
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| 30 | </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>
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| 31 | by using the navigator for tracking as shown above, the actual
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| 32 | particle gets also -relocated- in the specified position. Therefore,
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| 33 | if this information is needed during tracking time, in order to
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| 34 | avoid affecting tracking, you should either use an alternative
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| 35 | G4Navigator object (which you then assign to your world-volume),
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| 36 | or you access the information through the track or touchable as
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| 37 | specified in the FAQ for tracking and steps.
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| 38 | </p></div><p>
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| 39 | </p></td></tr><tr class="question"><td align="left" valign="top"><a name="qanda.Geometry.DghtVol"></a><a name="id553875"></a><b>Q:</b></td><td align="left" valign="top"><p>
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| 40 | How can I access the daughter volumes of a specific physical volume?
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| 41 | </p></td></tr><tr class="answer"><td align="left" valign="top"><b>A:</b></td><td align="left" valign="top"><p>
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| 42 | Through the associated logical volume.
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| 43 | </p><div class="informalexample"><pre class="programlisting">
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| 44 | G4VPhysicalVolume* myPVolume = ....;
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| 45 | G4LogicalVolume* myLVolume = myPVolume->GetLogicalVolume();
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| 46 | for (G4int i=0; iGetNoDaughters(); i++)
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| 47 | myPVolume = myLVolume->GetDaughter(i);
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| 48 | </pre></div><p>
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| 49 | </p></td></tr><tr class="question"><td align="left" valign="top"><a name="qanda.Geometry.CpyNum"></a><a name="id553906"></a><b>Q:</b></td><td align="left" valign="top"><p>
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| 50 | How can I identify the exact copy-number of a specific physical volume
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| 51 | in my mass geometry? I tried with GetCopyNo() from my physical volume
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| 52 | pointer, but it doesn't seem to work!
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| 53 | </p></td></tr><tr class="answer"><td align="left" valign="top"><b>A:</b></td><td align="left" valign="top"><p>
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| 54 | The correct way to identify -uniquely- a physical volume in your mass
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| 55 | geometry is by using the touchables (see also section 4.1.5 of the
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| 56 | User's Guide for Application Developers), as follows:
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| 57 | </p><div class="informalexample"><pre class="programlisting">
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| 58 | G4Step* aStep = ..;
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| 59 | G4StepPoint* preStepPoint = aStep->GetPreStepPoint();
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| 60 | G4TouchableHandle theTouchable = preStepPoint->GetTouchableHandle();
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| 61 | G4int copyNo = theTouchable->GetCopyNumber();
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| 62 | G4int motherCopyNo = theTouchable->GetCopyNumber(1);
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| 63 | </pre></div><p>
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| 64 |
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| 65 | where <code class="literal">Copy</code> here stays for any duplicated instance of
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| 66 | a physical volume, either if it is a <code class="literal">G4PVPlacement</code>
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| 67 | (multiple placements of the same logical volume) or a
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| 68 | <code class="literal">G4PVReplica/G4PVParameterised</code>.
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| 69 | The method <code class="literal">GetCopyNo()</code> is meant to return only the
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| 70 | serial number of placements not duplicated in the geometry tree.
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| 71 | </p></td></tr><tr class="question"><td align="left" valign="top"><a name="qanda.Geometry.ConvGtoL"></a><a name="id553963"></a><b>Q:</b></td><td align="left" valign="top"><p>
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| 72 | How can I determine the exact position in global coordinates in my mass
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| 73 | geometry during tracking and how can I convert it to coordinates local
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| 74 | to the current volume ?
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| 75 | </p></td></tr><tr class="answer"><td align="left" valign="top"><b>A:</b></td><td align="left" valign="top"><p>
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| 76 | You need again to do it through the touchables (see also section 4.1.5
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| 77 | of the User's Guide for Application Developers), as follows:
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| 78 | </p><div class="informalexample"><pre class="programlisting">
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| 79 | G4Step* aStep = ..;
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| 80 | G4StepPoint* preStepPoint = aStep->GetPreStepPoint();
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| 81 | G4TouchableHandle theTouchable = preStepPoint->GetTouchableHandle();
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| 82 | G4ThreeVector worldPosition = preStepPoint->GetPosition();
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| 83 | G4ThreeVector localPosition = theTouchable->GetHistory()->
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| 84 | GetTopTransform().TransformPoint(worldPosition);
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| 85 | </pre></div><p>
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| 86 |
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| 87 | where <code class="literal">worldPosition</code> here stays for the position related
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| 88 | to the world volume, while <code class="literal">localPosition</code> refers to the
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| 89 | coordinates local to the volume where the particle is currently placed.
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| 90 | </p></td></tr></tbody></table></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch10s02.html"><img src="AllResources/IconsGIF/prev.gif" alt="Prev"></a> </td><td width="20%" align="center"><a accesskey="u" href="ch10.html"><img src="AllResources/IconsGIF/up.gif" alt="Up"></a></td><td width="40%" align="right"> <a accesskey="n" href="ch10s04.html"><img src="AllResources/IconsGIF/next.gif" alt="Next"></a></td></tr><tr><td width="40%" align="left" valign="top">FAQ.2.
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| 91 | Run Time Problems
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| 92 | </td><td width="20%" align="center"><a accesskey="h" href="index.html"><img src="AllResources/IconsGIF/home.gif" alt="Home"></a></td><td width="40%" align="right" valign="top"> FAQ.4.
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| 93 | Tracks and steps
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| 94 | </td></tr></table></div></body></html>
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