[Rtk-users] Error message: cannot account for detector displacement larger than 50% of panel size

[vincent]

Hi Simon,

thank you very much for your quick reply.  Your analysis was correct, I 
needed to redefine the center.

I wish you a very nice day,

best regards,

Vincent



On 2018-10-01 20:43, Simon Rit wrote:
> Hi Vincent,
> This generally occurs when your detector offset is not adequately 
> passed to the geometry. When you say that you have "5.2mm and -8mm" 
> offsets, I guess it is with respect to a centered geometry, where the 
> central ray hits the detector. For this to be the case in RTK, you 
> must check that the coordinate (0,0) mm corresponds to the center of 
> the detector. By default, I guess that tif puts it in the corner. So 
> you probably need to add to rtkprojections an option like --neworigin 
> xorig,yorig,0 where xorig and yorig is something like 
> -0.5*(npixels-1)*spacing.
> If that doesn't help, you don't need to share the data, the mhd 
> headers are sufficient to test the geometry.
> Good luck!
> Simon
>
> On Mon, Oct 1, 2018 at 5:13 PM vincent <vl at xris.eu 
> <mailto:vl at xris.eu>> wrote:
>
>     Hi everyone,
>
>     I am facing a problem when I try to reconstruct an object. I'll
>     try to
>     be as complete as possible in the description.
>
>     I acquired 18000 views from a custom-made ct scanner, of which I
>     extracted 360 for the sake of reconstruction speed for my tests. The
>     images are cropped to 1001*1761 pixels.  An external calibration
>     program
>     estimated that the x and y detector offsets where 5.2mm and -8mm
>     respectively.  The sdd and sid are 983mm and 483mm.  I used those
>     value
>     to generate a simulated geometry.
>
>     I then created a projection volume with the command
>
>     rtkprojections -v  -o rec1Proj.mha -p . -r cropped.*.tif --i0 7000
>     where
>     I estimated the i0 value on the images background (for the sake of
>     completeness, I also tested with the automatic value which
>     resulted in
>     the same problem)
>
>     Finally, I wanted to reconstruct the volume with the command
>
>     rtkfdk  -g geoCT.xml -p . -r rec1Proj.mha  --spacing 0.2 --dimension
>     1761,1761,1761 -v -o recFDK.mha  --hardware cuda
>
>
>     The exact error message is:
>
>     Reconstructing and writing... ExceptionObject caught with
>     writer->Update() in file
>     ~/IPTools/RTK/RTK/applications/rtkfdk/rtkfdk.cxx line 218
>
>     itk::ExceptionObject (0x1cf4b90)
>     Location: "unknown"
>     File: ~/IPTools/RTK/RTK/code/rtkDisplacedDetectorImageFilter.hxx
>     Line: 155
>     Description: itk::ERROR: Cannot account for detector displacement
>     larger
>     than 50% of panel size. Corner inf=2.55504 and corner sup=100.826
>
>     I had a look at the aforementionned line in the
>     rtkDisplacedDetectorImageFilter.hxx file but I didn't really
>     understand
>     how the corners are computed in the
>     inputPtr->TransformIndexToPhysicalPoint(inputPtr->GetLargestPossibleRegion().GetIndex(),
>
>     corner function.
>
>     I have no problem sharing the projections if needed, but they
>     weight 1.3
>     Go altogether.
>
>
>     I thank you very much in advance for any kind of help you can provide.
>
>     Best regards,
>
>     Vincent
>
>
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