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<p class="MsoNormal">Dear RTK users,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="EN-GB">I am struggling with understanding RTK‘s projection geometry.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">My measurement setup is that source and detector are fixed and the object is on a rotating plate.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">The rotation axis has a slight horizontal offset as it can be seen in projections measured with 180° angular shift.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">My assumptions based on <a href="http://www.openrtk.org/Doxygen/DocGeo3D.html">
http://www.openrtk.org/Doxygen/DocGeo3D.html</a> now are:<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span lang="EN-GB"><span style="mso-list:Ignore">1)<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-GB">The isocenter is fix and in my case the center of the rotation axis of the plate.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span lang="EN-GB"><span style="mso-list:Ignore">2)<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-GB">The documentation says that “The source position is defined with respect to the isocenter with three parameters”.<o:p></o:p></span></p>
<p class="MsoListParagraph"><span lang="EN-GB">So I should apply the estimated horizontal offset as SourceOffsetX.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo1"><![if !supportLists]><span lang="EN-GB"><span style="mso-list:Ignore">3)<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-GB">The documentation also says that “The detector position is defined with respect to the source with three parameters”<o:p></o:p></span></p>
<p class="MsoListParagraph"><span lang="EN-GB">Does this imply that SourceOffsetX also has an impact on the detector position, e.g. the detector origin (0,0)?<o:p></o:p></span></p>
<p class="MsoListParagraph"><span lang="EN-GB">Because this would be contrary to the next sentence of the documentation:<o:p></o:p></span></p>
<p class="MsoListParagraph"><span lang="EN-GB">“(ProjectionOffsetX,ProjectionOffsetY,SourceToIsocenterDistance-SourceToDetectorDistance) are the coordinates of the detector origin (0,0) in the rotated coordinated system.”<o:p></o:p></span></p>
<p class="MsoListParagraph"><span lang="EN-GB">So either the detector is also positioned with respect to the isocenter, then the coordinates are (ProjectionOffsetX,ProjectionOffsetY,SourceToIsocenterDistance-SourceToDetectorDistance)<o:p></o:p></span></p>
<p class="MsoListParagraph"><span lang="EN-GB">or respect to the source and should have (ProjectionOffsetX+ SourceOffsetX,ProjectionOffsetY+SourceOffsetY,SourceToIsocenterDistance-SourceToDetectorDistance)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Is this correct or did I miss something?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Basically it comes down to the question: Do I need to compensate for the horizontal offset of the rotation axis in ProjectionOffsetX as well or is it already handled by setting SourceOffsetX?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="color:#145A6E;mso-fareast-language:DE">Best,<o:p></o:p></span></b></p>
<p class="MsoNormal"><b><span style="color:#145A6E;mso-fareast-language:DE">Moritz<o:p></o:p></span></b></p>
<p class="MsoNormal"><o:p> </o:p></p>
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