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

[Simon Rit]

Indeed, I have taken it as an assertion! Yes, since the source
position is the same for all pixels of a projection image, it gives
divergent rays focused on the source position.
Simon

On Tue, Jun 23, 2015 at 3:12 PM, "Robert Calließ"
<Robert.Calliess at gmx.de> wrote:
> Hello,
> thank you for the answer. I wanted to get a short feedback to the last part
> of my email.
> I guess I missed the "?" .
>
>> 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. ??
> ??
>
> best regards,
> Robert
>
> Gesendet: Dienstag, 23. Juni 2015 um 15:08 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 ?
> 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
>>>
>>>
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Rtk-users mailing list
>>> Rtk-users at public.kitware.com
>>> http://public.kitware.com/mailman/listinfo/rtk-users
>>>
>>
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