Hi, I guess the confusion comes from "“The detector position is defined with respect to the source with three parameters”. I guess we wrote this due to the use of source distances in the third coordinate SourceToIsocenterDistance-SourceToDetectorDistance, but it's with respect to the isocenter indeed. Any amendment to the documentation is welcomed (via a github PR preferably). 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 GetSourcePosition <http://www.openrtk.org/Doxygen/classrtk_1_1ThreeDCircularProjectionGeometry.html#a8251a17e5ab907935da8b734ff4fb798> and GetProjectionCoordinatesToFixedSystemMatrix <http://www.openrtk.org/Doxygen/classrtk_1_1ThreeDCircularProjectionGeometry.html#ae072bdb4511a44615fb12ac48538be79*> . Simon
On Thu, May 12, 2022 at 2:08 PM Moritz Schaar <sch...@imt.uni-luebeck.de> wrote: > Dear RTK users, > > > > I am struggling with understanding RTK‘s projection geometry. > > My measurement setup is that source and detector are fixed and the object > is on a rotating plate. > > The rotation axis has a slight horizontal offset as it can be seen in > projections measured with 180° angular shift. > > > > My assumptions based on http://www.openrtk.org/Doxygen/DocGeo3D.html now > are: > > 1) The isocenter is fix and in my case the center of the rotation > axis of the plate. > > 2) The documentation says that “The source position is defined with > respect to the isocenter with three parameters”. > > So I should apply the estimated horizontal offset as SourceOffsetX. > > 3) The documentation also says that “The detector position is > defined with respect to the source with three parameters” > > Does this imply that SourceOffsetX also has an impact on the detector > position, e.g. the detector origin (0,0)? > > Because this would be contrary to the next sentence of the documentation: > > “(ProjectionOffsetX,ProjectionOffsetY,SourceToIsocenterDistance-SourceToDetectorDistance) > are the coordinates of the detector origin (0,0) in the rotated coordinated > system.” > > So either the detector is also positioned with respect to the isocenter, > then the coordinates are > (ProjectionOffsetX,ProjectionOffsetY,SourceToIsocenterDistance-SourceToDetectorDistance) > > or respect to the source and should have (ProjectionOffsetX+ > SourceOffsetX,ProjectionOffsetY+SourceOffsetY,SourceToIsocenterDistance-SourceToDetectorDistance) > > > > Is this correct or did I miss something? > > 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? > > > > > > *Best,* > > *Moritz* > > > _______________________________________________ > Rtk-users mailing list > Rtk-users@public.kitware.com > https://public.kitware.com/cgi-bin/mailman/listinfo/rtk-users >
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