<div dir="ltr"><div>Hi,</div><div>I guess the confusion comes from "“The detector position is defined with respect to the source with three parameters”. <span lang="EN-GB">I guess we wrote this due to the use of source distances in the third coordinate <span lang="EN-GB">SourceToIsocenterDistance-SourceToDetectorDistance, but it's with respect to the isocenter indeed. Any amendment to the documentation is welcomed (via a github PR preferably).</span></span></div><div><span lang="EN-GB"><span lang="EN-GB">In general, I strongly suggest to play with the python wrappings to understand what positions are taken by the source and a detector coordinate with the methods <a href="http://www.openrtk.org/Doxygen/classrtk_1_1ThreeDCircularProjectionGeometry.html#a8251a17e5ab907935da8b734ff4fb798">GetSourcePosition</a> and <a href="http://www.openrtk.org/Doxygen/classrtk_1_1ThreeDCircularProjectionGeometry.html#ae072bdb4511a44615fb12ac48538be79*">GetProjectionCoordinatesToFixedSystemMatrix</a></span></span>.</div><div>Simon<br></div><div><span lang="EN-GB"><span lang="EN-GB"></span></span></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, May 12, 2022 at 2:08 PM Moritz Schaar <<a href="mailto:schaar@imt.uni-luebeck.de">schaar@imt.uni-luebeck.de</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div lang="DE">
<div class="gmail-m_-3074165621266056184WordSection1">
<p class="MsoNormal">Dear RTK users,<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><span lang="EN-GB">I am struggling with understanding RTK‘s projection geometry.<u></u><u></u></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.<u></u><u></u></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.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">My assumptions based on <a href="http://www.openrtk.org/Doxygen/DocGeo3D.html" target="_blank">
http://www.openrtk.org/Doxygen/DocGeo3D.html</a> now are:<u></u><u></u></span></p>
<p class="gmail-m_-3074165621266056184MsoListParagraph"><u></u><span lang="EN-GB"><span>1)<span style="font:7pt "Times New Roman"">
</span></span></span><u></u><span lang="EN-GB">The isocenter is fix and in my case the center of the rotation axis of the plate.<u></u><u></u></span></p>
<p class="gmail-m_-3074165621266056184MsoListParagraph"><u></u><span lang="EN-GB"><span>2)<span style="font:7pt "Times New Roman"">
</span></span></span><u></u><span lang="EN-GB">The documentation says that “The source position is defined with respect to the isocenter with three parameters”.<u></u><u></u></span></p>
<p class="gmail-m_-3074165621266056184MsoListParagraph"><span lang="EN-GB">So I should apply the estimated horizontal offset as SourceOffsetX.<u></u><u></u></span></p>
<p class="gmail-m_-3074165621266056184MsoListParagraph"><u></u><span lang="EN-GB"><span>3)<span style="font:7pt "Times New Roman"">
</span></span></span><u></u><span lang="EN-GB">The documentation also says that “The detector position is defined with respect to the source with three parameters”<u></u><u></u></span></p>
<p class="gmail-m_-3074165621266056184MsoListParagraph"><span lang="EN-GB">Does this imply that SourceOffsetX also has an impact on the detector position, e.g. the detector origin (0,0)?<u></u><u></u></span></p>
<p class="gmail-m_-3074165621266056184MsoListParagraph"><span lang="EN-GB">Because this would be contrary to the next sentence of the documentation:<u></u><u></u></span></p>
<p class="gmail-m_-3074165621266056184MsoListParagraph"><span lang="EN-GB">“(ProjectionOffsetX,ProjectionOffsetY,SourceToIsocenterDistance-SourceToDetectorDistance) are the coordinates of the detector origin (0,0) in the rotated coordinated system.”<u></u><u></u></span></p>
<p class="gmail-m_-3074165621266056184MsoListParagraph"><span lang="EN-GB">So either the detector is also positioned with respect to the isocenter, then the coordinates are (ProjectionOffsetX,ProjectionOffsetY,SourceToIsocenterDistance-SourceToDetectorDistance)<u></u><u></u></span></p>
<p class="gmail-m_-3074165621266056184MsoListParagraph"><span lang="EN-GB">or respect to the source and should have (ProjectionOffsetX+ SourceOffsetX,ProjectionOffsetY+SourceOffsetY,SourceToIsocenterDistance-SourceToDetectorDistance)<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">Is this correct or did I miss something?<u></u><u></u></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?<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><b><span style="color:rgb(20,90,110)">Best,<u></u><u></u></span></b></p>
<p class="MsoNormal"><b><span style="color:rgb(20,90,110)">Moritz<u></u><u></u></span></b></p>
<p class="MsoNormal"><u></u> <u></u></p>
</div>
</div>
_______________________________________________<br>
Rtk-users mailing list<br>
<a href="mailto:Rtk-users@public.kitware.com" target="_blank">Rtk-users@public.kitware.com</a><br>
<a href="https://public.kitware.com/cgi-bin/mailman/listinfo/rtk-users" rel="noreferrer" target="_blank">https://public.kitware.com/cgi-bin/mailman/listinfo/rtk-users</a><br>
</blockquote></div>