[Rtk-users] Rotation before and during rktprojections

[Simon Rit]

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> 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> 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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>>
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