---------- Forwarded message ---------- From: Samuel Gerber <samuel.ger...@kitware.com> Date: Fri, Aug 18, 2017 at 10:01 AM Subject: Re: [Rtk-users] Projection Geometry and Image Origins To: Simon Rit <simon....@creatis.insa-lyon.fr>
Thank you Simon. One more clarification question Are the SID and SDD parameters measured in units of the input volume spacing in z? On Fri, Aug 18, 2017 at 2:53 AM, Simon Rit <simon....@creatis.insa-lyon.fr> wrote: > Dear Samuel, > Here is how I'd explain it: there are two ITK images, a volume and a > stack of projections. Each image has its own coordinate system, > defined in ITK by the Origin, the Spacing and the Direction. The > geometry links the volume coordinate system to each projection > coordinate system (which is common for all projections) of the stack > using 9 parameters per projection. > In order to center the volume on the projections, you have different > scenarios. Let's take one example: > - the volume is centered around (0,0,0) (e.g., > origin=(-127,-127,-127), spacing=(2,2,2) and size=(128,128,128)), > - the projection is centered around (0,0) (e.g., same values as for > the volume. Note that the third coordinate is ignored by RTK). > - then the projection is centered on the volume if all offsets are 0. > If the projection had not been centered (e.g., origin=(0,0,0)), then > you can create exactly the same geometry by setting > ProjectionOffsetX=ProjectionOffsetY=127. > I hope this helps, > Simon > > On Thu, Aug 17, 2017 at 3:45 PM, Samuel Gerber > <samuel.ger...@kitware.com> wrote: > > Hi, > > > > I'm curious about the settings for the different origins when setting up > a > > ProjectionGeometry, in particular ThreeDCircularProjectionGeometry. > > > > As far as I understand there is three origins: > > - The projection geometry origin at (0, 0, 0) > > - The input image origin > > - The projection image origin > > > > In order to center the projection on the input image I assume that I will > > have to use the offset parameters to shift the source and detector so > that > > they are centered on the input image in physical coordinates. > > How does the projection image origin come into play? > > > > Thanks > > Samuel > > > > -- > > Samuel Gerber > > R&D Engineer > > Kitware, Inc. > > > > _______________________________________________ > > Rtk-users mailing list > > Rtk-users@public.kitware.com > > http://public.kitware.com/mailman/listinfo/rtk-users > > > -- Samuel Gerber R&D Engineer Kitware, Inc. -- Samuel Gerber R&D Engineer Kitware, Inc.
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