[Rtk-users] Rotation before and during rktprojections

[vincent]

Hi Simon,

I will clean my code and submit today or Monday then.

best regards,

V.

On 23.04.20 18:13, Simon Rit wrote:
> Thanks for the update. It's not a bad idea to include this in the 
> projections reader but ideally, it should calculate the permutation 
> parameter automatically from the geometry. If it's optional, it's not 
> a bad idea to have it in the projections reader pipeline, don't 
> hesitate to submit if you have a clean PR.
>
> On Thu, Apr 23, 2020 at 3:56 PM vincent <vl at xris.eu 
> <mailto:vl at xris.eu>> wrote:
>
>     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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