[Rtk-users] forward projectors - considering perspective view ?

[Simon Rit]

No, the isocenter is the center of rotation which is also used as the
origin of the coordinate system of the tomography in RTK.
Simon

On Tue, Jun 23, 2015 at 3:04 PM, "Robert Calließ"
<Robert.Calliess at gmx.de> wrote:
> Hello Simon,
> thank you for your fast reply. It was a question in general.
> I had a look at the ThreeDCircularProjectionGeometry file. But generally
> it should be the same as I described in my email. Also for the
> joseph projector, spanning the ray from source to detector position (pixel).
> This automatically gives divergent rays.
>
> I have another question. Is the isocenter the center of the object ?
>
> best regards,
> Robert
>
> Gesendet: Dienstag, 23. Juni 2015 um 14:00 Uhr
> Von: "Simon Rit" <simon.rit at creatis.insa-lyon.fr>
> An: "Robert Calließ" <Robert.Calliess at gmx.de>
> Cc: "rtk-users at public.kitware.com" <rtk-users at public.kitware.com>
> Betreff: Re: [Rtk-users] forward projectors - considering perspective view ?
> Hi,
> I'm not sure I understand exactly what you mean but it seems to me
> that yes, it should, i.e.
> - the source position is set according to the description you have
> given in your ThreeDCircularProjectionGeometry. Computation of the
> source position is done in
> ThreeDCircularProjectionGeometry::GetSourcePosition, you can check.
> - idem for the pixel position of your detector. Computation is a bit
> more subtle because it uses a matrix,
> ThreeDCircularProjectionGeometry::GetProjectionCoordinatesToFixedSystemMatrix
> The whole thing is for example done in
> rtk::JosephForwardProjectionImageFilter
> Are you asking because you've observed something unexpected?
> Simon
>
> On Tue, Jun 23, 2015 at 1:30 PM, "Robert Calließ"
> <Robert.Calliess at gmx.de> wrote:
>> Hello,
>> I've got a questions regarding to the forward projectors for the S-ART
>> reconstruction.
>> Let's say there are some xray projection images from an xray machine taken
>> with a circular trjectory (cone beam)
>> The perspective view for these real projection images have been taken into
>> account, of course.
>> The forward projector creates a virtual projection image of the volume to
>> be
>> reconstructed. When this forward projection
>> takes place does the forward projector also take into account the
>> perspective view of the real CT system ?
>>
>> Let's say we have a simple raycast forward projector.
>> The geometry (focus, object, detector) are all given in real world units
>> where the object's center is (0, 0, 0).
>> By "real world units" I mean the physical dimensions from the CT system.
>> For
>> instance, if the distance between
>> the object's center and the xray-source is 500mm, the the xray-source
>> position is (0,0, -500.0).
>>
>> So the virtual projection image is created as follows:
>> 1: setup ray from xray-source to the current detector pixel
>> 2: determine entry point and exit point of this ray with the physical
>> bounding volume
>> 3: sample the volume along the ray, from entry point to exit point
>>
>> Does these steps per se include the perspective view ? Since the geomtry
>> (position of focus object detector) for the reconstruction is modeled
>> to imitate the real CT system's geometry, it should ?
>>
>>
>>
>> best regards,
>> Robert
>>
>>
>>
>>
>>
>>
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>
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