[Rtk-users] Fwd: Projection Geometry and Image Origins

[Samuel Gerber]

---------- Forwarded message ----------
From: Samuel Gerber <samuel.gerber at kitware.com>
Date: Fri, Aug 18, 2017 at 10:01 AM
Subject: Re: [Rtk-users] Projection Geometry and Image Origins
To: Simon Rit <simon.rit at 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.rit at 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.gerber at 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 at 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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