Hi, It's still not clear to me but what is helpful is to think in terms of source trajectory wrt the object. Trajectory 1: if I understand, you move the source on two circles plus one point. I don't know of a FBP algorithm to reconstruct this, but there might be one. I would consider iterative reconstruction first. Trajectory 2: your trajectory is a point, the source does not move with respect ot the object since it lies on the rotation axis. So each projection contains exactly the same information up to a simple 2D projection deformation. So it's hopeless to reconstruct from one projection only. To create the correct geometry, I would suggest using the function AddProjection <https://github.com/SimonRit/RTK/blob/master/code/rtkThreeDCircularProjectionGeometry.h#L92> for which you provide the source and detector positions plus the 3D coordinates of the two axes of the coordinate system of the projection. I hope this helps Simon
On Tue, Oct 10, 2017 at 5:43 PM, "Robert Calließ" <robert.calli...@gmx.de> wrote: > Hello, > thank you for the fast reply. > To answer your questions first. > In this case the abbrevation pcb stands for printed circuit board. > Next point is the trajectory we are currently handling with. > Please see the attached image "trajectory.png". There are two schematics > showing the side view and top view for trajectory type 1 > and a side-view for trajectory type 2. > > For type 1: > The xray source is fixed. The pcb is clamped within a transport, so the > pcb and the detector are moveable with in the xy plane. > As you can see at the image, the pcb moves along a circular path but the > pcb itself is not rotating. And let's assume that the iso ray > always passes through the centre of the pcb and the centre of the detector. > > For type 2: > The xray source is fixed and the detector is tilted. The pcb lies centred > in the middle of a table. So that the pcb rotates around its centre > around the z-axis. > > > I hope this makes clear what trajectory i'm dealing with. Thank you. > > Kind regards, > Robert C. > > > > > > > *Gesendet:* Dienstag, 10. Oktober 2017 um 15:31 Uhr > *Von:* "Cyril Mory" <cyril.m...@creatis.insa-lyon.fr> > *An:* "Robert Calliess" <robert.calli...@gmx.de>, > rtk-users@public.kitware.com > *Betreff:* Re: [Rtk-users] FDK for planar ct > > Dear Robert, > > Your description of the trajectory is very obscure to me. Maybe you have a > very unusual X-ray system. Could you make the following points clear : > > - what is a PCB ? > > - what is fixed/moving in your system (we need this information for the > object, the source and the detector), and what kind of trajectories have > the moving parts ? > > - can you re-draw your sketch with just 2 or 3 positions (ideally, on > similar but separate drawings), each one with the object, the source and > the detector ? > > If you do that, we should have a clear understanding of how your > acquisition goes, and be able to give you appropriate advice. > > Best regards, > > Cyril > > On 10/10/2017 15:02, Robert Calliess wrote: > > Hello rtk users, > > I have question to the RTK FDK Filter. As far as I understand from to the > fourier slice theorem the object to be reconstructed needs a circular > trajectory and needs to rotate its own centre. > > Please have a look at the attached sketch. With this planar trajectory > (Object, a PCB, is moved on a circle trajectpry “in-plane”, PCB itself is > not rotating) do I need > > a special filtering if I want to use FDK for planar CT with respect to the > sketched trajectory ? I tried a circular in-plane trajectory where the PCB > is centred and rotates > > around its centre point. And with 100 projections I get good results. But > with the trajectory I described (sketch, attached image) the results are > not so good. > > Because of the row-wise ramp filter It looks like there is a directional > dependency. My assumption is, and with respect to fourier slice theorem, > that the missing object > > rotation (rotation around itself) causes there directional effects. > > > > So my questions to the experts are. Do I need to apply a special filtering > before backprojecting with FDK or is it just the wrong > > algorithm for this kind of trajectory ? > > > > kind regards, > > Robert C. > > > _______________________________________________ > Rtk-users mailing > listRtk-users@public.kitware.comhttp://public.kitware.com/mailman/listinfo/rtk-users > > > _______________________________________________ > Rtk-users mailing list > Rtk-users@public.kitware.com > http://public.kitware.com/mailman/listinfo/rtk-users > >
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