[Rtk-users] geometry offsets

[bambykaa 1]

Hi,
hovewer i think that origin in common cases (central ray intersects detector's plane at the center ) calculates as -1 * (W / 2 - SPACING / 2), so my W: 1024 - > -1 * (512 * 0.0957 - 0.0957 /  2)
anyway i have good volumes from another tomographs, the difference is that isocenter not at the center of xray and detector
okay i will investigate my problem and keep you informed if i will make some progresses

13.04.2015, 12:50, "Simon Rit" <simon.rit at creatis.insa-lyon.fr>:
> 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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