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1<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>FAQ.4.  Tracks and steps</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="ch10s03.html" title="FAQ.3.  Geometry"><link rel="next" href="ch10s05.html" title="FAQ.5.  Physics and cuts"><script language="JavaScript">
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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.4. 
9Tracks and steps
10</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch10s03.html"><img src="AllResources/IconsGIF/prev.gif" alt="Prev"></a> </td><th width="60%" align="center">Chapter FAQ. 
11Frequentry Asked Questions
12</th><td width="20%" align="right"> <a accesskey="n" href="ch10s05.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.TrackSteps"></a>FAQ.4. 
13Tracks and steps
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.TrackSteps.AccssTrkInfo"></a><a name="id553775"></a><b>Q:</b></td><td align="left" valign="top"><p>
15 How can I access the track information through the step object and
16 what information am I allowed to access ?
17</p></td></tr><tr class="answer"><td align="left" valign="top"><b>A:</b></td><td align="left" valign="top"><p>
18 </p><p>
19 A <code class="literal">G4Step</code> object consists of two points:
20 </p><div class="informalexample"><pre class="programlisting">
21 G4StepPoint* point1 = step-&gt;GetPreStepPoint();
22 G4StepPoint* point2 = step-&gt;GetPostStepPoint();
23 </pre></div><p>
24 </p><p>
25
26 </p><p>
27 To get their positions in the global coordinate system:
28 </p><div class="informalexample"><pre class="programlisting">
29 G4ThreeVector pos1 = point1-&gt;GetPosition();
30 G4ThreeVector pos2 = point2-&gt;GetPosition();
31 </pre></div><p>
32 </p><p>
33
34 </p><p>
35 Hereafter we call current volume the volume where the step has just
36 gone through. Geometrical informations are available from
37 <code class="literal">preStepPoint</code>.
38 <code class="literal">G4VTouchable</code> and its derivates keep these geometrical
39 informations. We retrieve a touchable by creating a handle for it:
40
41 </p><div class="informalexample"><pre class="programlisting">
42 G4TouchableHandle touch1 = point1-&gt;GetTouchableHandle();
43 </pre></div><p>
44 </p><p>
45
46 </p><p>
47 To get the current volume:
48 </p><div class="informalexample"><pre class="programlisting">
49 G4VPhysicalVolume* volume = touch1-&gt;GetVolume();
50 </pre></div><p>
51 </p><p>
52
53 </p><p>
54 To get its name:
55 </p><div class="informalexample"><pre class="programlisting">
56 G4String name = volume-&gt;GetName();
57 </pre></div><p>
58 </p><p>
59
60
61 </p><p>
62 To get the physical volume copy number:
63 </p><div class="informalexample"><pre class="programlisting">
64 G4int copyNumber = touch1-&gt;GetCopyNumber();
65 </pre></div><p>
66 </p><p>
67
68 </p><p>
69 To get logical volume:
70 </p><div class="informalexample"><pre class="programlisting">
71 G4LogicalVolume* lVolume = volume-&gt;GetLogicalVolume();
72 </pre></div><p>
73 </p><p>
74
75
76 </p><p>
77 To get the associated material: the following statements are equivalent:
78 </p><div class="informalexample"><pre class="programlisting">
79 G4Material* material = point1 -&gt;GetMaterial();
80 G4Material* material = lVolume -&gt;GetMaterial();
81 </pre></div><p>
82 </p><p>
83
84
85 </p><p>
86 To get the geometrical region:
87 </p><div class="informalexample"><pre class="programlisting">
88 G4Region* region = lVolume-&gt;GetRegion();
89 </pre></div><p>
90 </p><p>
91
92
93 </p><p>
94 To get its mother volume:
95 </p><div class="informalexample"><pre class="programlisting">
96 G4VPhysicalVolume* mother = touch1-&gt;GetVolume(depth=1);
97 grandMother: depth=2 ...etc...
98 </pre></div><p>
99 </p><p>
100
101
102 </p><p>
103 To get the copy number of the mother volume:
104 </p><div class="informalexample"><pre class="programlisting">
105 G4int copyNumber = touch1-&gt;GetCopyNumber(depth=1);
106 grandMother: depth=2 ...etc...
107 </pre></div><p>
108 </p><p>
109
110 </p><p>
111 To get the process which has limited the current step:
112 </p><div class="informalexample"><pre class="programlisting">
113 G4VProcess* aProcess = point2-&gt;GetProcessDefinedStep();
114 </pre></div><p>
115 </p><p>
116
117 </p><p>
118 To check that the particle has just entered in the current volume
119 (i.e. it is at the first step in the volume; the
120 <code class="literal">preStepPoint</code> is at the boundary):
121
122 </p><div class="informalexample"><pre class="programlisting">
123 if (point1-&gt;GetStepStatus() == fGeomBoundary)
124 </pre></div><p>
125 </p><p>
126
127 </p><p>
128 To check that the particle is leaving the current volume
129 (i.e. it is at the last step in the volume; the
130 <code class="literal">postStepPoint</code> is at the boundary):
131
132 </p><div class="informalexample"><pre class="programlisting">
133 if (point2-&gt;GetStepStatus() == fGeomBoundary)
134 </pre></div><p>
135 </p><p>
136
137 </p><p>
138 In the above situation, to get touchable of the next volume:
139
140 </p><div class="informalexample"><pre class="programlisting">
141 G4TouchableHandle touch2 = point2-&gt;GetTouchableHandle();
142 </pre></div><p>
143
144 From <code class="literal">touch2</code>, all informations on the next
145 volume can be retrieved as above.
146 </p><p>
147
148 </p><p>
149 Physics quantities are available from the step
150 (<code class="literal">G4Step</code>) or from the track (<code class="literal">G4Track</code>).
151 </p><p>
152
153 </p><p>
154 To get the energy deposition, step length, displacement and time
155 of flight spent by the current step:
156 </p><div class="informalexample"><pre class="programlisting">
157 G4double eDeposit = step-&gt;GetTotalEnergyDeposit();
158 G4double sLength = step-&gt;GetStepLength();
159 G4ThreeVector displace = step-&gt;GetDeltaPosition();
160 G4double tof = step-&gt;GetDeltaTime();
161 </pre></div><p>
162 </p><p>
163
164 </p><p>
165 To get momentum, kinetic energy and global time (time since the
166 beginning of the event) of the track after the completion of the
167 current step:
168 </p><div class="informalexample"><pre class="programlisting">
169 G4Track* track = step-&gt;GetTrack();
170 G4ThreeVector momentum = track-&gt;GetMomentum();
171 G4double kinEnergy = track-&gt;GetKineticEnergy();
172 G4double globalTime = track-&gt;GetGlobalTime();
173 ...etc...
174 </pre></div><p>
175
176 </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Remark</h3><p>
177 To transform a position from the global coordinate system to the
178 local system of the current volume, use the
179 <code class="literal">preStepPoint</code> transformation, as described in the
180 <a href="ch10s03.html#qanda.Geometry.ConvGtoL">geometry section</a> above.
181 </p></div><p>
182 </p><p>
183</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="ch10s03.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="ch10s05.html"><img src="AllResources/IconsGIF/next.gif" alt="Next"></a></td></tr><tr><td width="40%" align="left" valign="top">FAQ.3. 
184Geometry
185 </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.5. 
186Physics and cuts
187</td></tr></table></div></body></html>
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