[Rtk-users] geometry offsets

[Simon Rit]

Hi,
I'm afraid it's in your hands from here, at least I won't have time to
download and reconstruct your dataset. I don't understand the
computation of the offset in the proj_sub.mhd file. Shouldn't it be
-1 * (512 * 0.0957 - 0.0957) / 2  -1 *(500 * 0.096 - 0.096) / 2 0
?
Simon

On Wed, Apr 8, 2015 at 10:32 AM, bambykaa 1 <bambykaa at yandex.ru> wrote:
> Ok. But i still have problems with reconstruction. Could you check me
> please...
> My geomerty: source to detector 396.8 mm, source to iso 327.3 mm, iso center
> offset approximately calculated from projection 0.71775, gantry, 100 shots,
> 1 degree for each shot.
> camera: 1024x1000,  pixel sizes 95.7um x 96um
>
> Firstly i converted all tif files to mhd via rtksubselect. Then:
> rtksimulatedgeometry -o geometry.xml --n 100 --arc=100 --sdd=396.8
> --sid=327.3  --proj_iso_x=-0.71775 --source_x=-0.71775
> rtkfdk -p . -r proj_sub.mhd -o fdk.mha -g geometry.xml --verbose --dimension
> 512,512,512 --spacing 0.0957,0.096,0.0957
>
> proj_sub.mhd:
> ObjectType = Image
> NDims = 3
> BinaryData = True
> BinaryDataByteOrderMSB = False
> CompressedData = False
> TransformMatrix = 1 0 0 0 1 0 0 0 1
> Offset = -48.95055 -47.952 0 < ---- i calc so: -1 * (512 * 0.0957 - 0.0957 /
> 2)  -1 *(500 * 0.096 - 0.096 / 2) 0
> CenterOfRotation = 0 0 0
> AnatomicalOrientation = RAI
> ElementSpacing = 0.0957 0.096 1
> DimSize = 1024 1000 100
> ElementType = MET_FLOAT
> ElementDataFile = proj_sub.raw
>
> Here is the raw file and few origin tifs :
> https://drive.google.com/file/d/0B9EY8AokXE8zbjdtUUQtVkFuM1U/view?usp=sharing
> https://drive.google.com/file/d/0B9EY8AokXE8zVi1RaDA2QzBwdDA/view?usp=sharing
>
> Volume is not as promising at all.  Probably some geometry information in
> this tomography system is incorrect, its just in development. (may be
> central ray is not intersecting in the center of detector, and etc ). And of
> course it can be cause of reconstruction problems. But, if suppose that
> information above is correct, is i specify it right ?
>
>
> 07.04.2015, 13:26, "Simon Rit" <simon.rit at creatis.insa-lyon.fr>:
>
> Hi,
> This is almost correct. I think the default origin is -127.5 in the second
> case so the option of the first case should have been
> "--origin=-27.5,-127.5". Then, there would have been no geometric difference
> for RTK, it comes down to a choice between shifting the origin of your image
> or setting a relative position of your image with respect to the volume.
> Note that if you have different offsets for each projection, only the second
> option is feasible.
>
> In RTK, the center-of-rotation is always (0,0,0). So you have to shift the
> rest if you want to shift it (source and detector position indeed).
> Simon
>
> On Mon, Apr 6, 2015 at 3:40 PM, bambykaa 1 <bambykaa at yandex.ru> wrote:
>
> Hello RTK users.
> Is there difference between this
> rtksimulatedgeometry -n 180 -o geometry.xml
> rtkprojectgeometricphantom -g geometry.xml -o projections.mha --spacing 1
> --dimension 256 --phantomfile SheppLogan.txt --origin=-28,-128
>
> and this
>
> rtksimulatedgeometry -n 180 -o geometry.xml  --proj_iso_x=100
> rtkprojectgeometricphantom -g geometry.xml -o projections.mha --spacing 1
> --dimension 256 --phantomfile SheppLogan.txt
>
> ?
>
> As i understand these sequences are identical and using for specifying
> detector offset.
>
> But if i want to specify iso center offset ? May be..
> rtksimulatedgeometry -n 180 -o geometry.xml --proj_iso_x=100 --source_x=100
> rtkprojectgeometricphantom -g geometry.xml -o projections.mha --spacing 1
> --dimension 256 --phantomfile SheppLogan.txt
> Is it right ?
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