[Rtk-users] Rotation before and during rktprojections

[vincent]

Hi,

just to bring some closure to that problem..

I didn't manage to adapt the ramp filter, so I instead modified 
rtkProjectionsReader to include an Orientation parameter that sets the 
right coefficients for an itkPermuteAxis filter.

I don't think it is worthy to be included in the official source, but I 
am happy to share if someone requires it.

Best regards,

Vincent

On 15.04.20 20:13, Simon Rit wrote:
> Hi Vincent,
> Everything you did is correct but rtkfdk always applies the ramp 
> filter along the first dimension and does not check if this 
> corresponds to the direction orthogonal to the rotation axis. For your 
> case, it is probably not so difficult to adapt the code. When there is 
> a small rotation, it is debatable whether one should ignore the 
> rotation for the ramp filter, resample the image, or recalculate the 
> filter in 2D (see our recent publication here 
> <https://doi.org/10.1088/1361-6560/ab7875> which has not been 
> implemented in RTK). I have opened an issue on github 
> <https://github.com/SimonRit/RTK/issues/335>, hopefully we'll find 
> time to fix this in the future (at least raise an exception above a 
> parametrable rotation threshold).
> Best regards,
> Simon
>
> On Wed, Apr 15, 2020 at 7:00 PM vincent <vl at xris.eu 
> <mailto:vl at xris.eu>> wrote:
>
>     Hi RTK community,
>
>     I hope everyone is doing well in those hard times.
>
>     I have a panel that is rotated by 90° on the CT system.  I used to
>     rotate the images back in the right orientation before building the
>     sinogram with rtkprojections, but then I thought I might give a
>     try at
>     the "newdirection" option.  Using the matrix [0 1 0 ; 1 0 0 ; 0 0 1]
>     gives the expected results.  So far so good. But when I try to
>     reconstruct the latter with the same geometric parameters than for
>     the
>     pre-rotated projections, I obtain a very blurry result (vs a sharp
>     one
>     in the first case).  I am obviously missing something, and I would
>     suspect I am not giving the right information to the rtkfdk
>     application.  So far, here is what I have tried:
>
>     -keep the projections in the initial orientation, but give the
>     "newdirection" option to the rtkfdk application,
>
>     -specify the "newdirection" in both rtkprojections and rtkfdk,
>
>     -turn to you for advice !
>
>     I thank you very much in advance for any help you might be able to
>     give.
>
>     Best regards,
>
>     Vincent
>
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