All distances in the geometry file are in the same unit as the image spacing (i.e., mm in most cases). I forgot to mention the geometry doc before http://www.openrtk.org/Doxygen/geometry.pdf
On Fri, Aug 18, 2017 at 4:03 PM, Samuel Gerber <[email protected]> wrote: > > ---------- Forwarded message ---------- > From: Samuel Gerber <[email protected]> > Date: Fri, Aug 18, 2017 at 10:01 AM > Subject: Re: [Rtk-users] Projection Geometry and Image Origins > To: Simon Rit <[email protected]> > > > 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 <[email protected] > > 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 >> <[email protected]> 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 >> > [email protected] >> > http://public.kitware.com/mailman/listinfo/rtk-users >> > >> > > > > -- > Samuel Gerber > R&D Engineer > Kitware, Inc. > > > > -- > Samuel Gerber > R&D Engineer > Kitware, Inc. > > _______________________________________________ > Rtk-users mailing list > [email protected] > http://public.kitware.com/mailman/listinfo/rtk-users > >
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