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<div>Hello Simon,</div>
<div>thank you for your fast reply. It was a question in general.</div>
<div>I had a look at the ThreeDCircularProjectionGeometry file. But generally</div>
<div>it should be the same as I described in my email. Also for the</div>
<div>joseph projector, spanning the ray from source to detector position (pixel).</div>
<div>This automatically gives divergent rays.</div>
<div> </div>
<div>I have another question. Is the isocenter the center of the object ?</div>
<div> </div>
<div>best regards,</div>
<div>Robert</div>
<div>
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<div style="margin:0 0 10px 0;"><b>Gesendet:</b> Dienstag, 23. Juni 2015 um 14:00 Uhr<br/>
<b>Von:</b> "Simon Rit" <simon.rit@creatis.insa-lyon.fr><br/>
<b>An:</b> "Robert Calließ" <Robert.Calliess@gmx.de><br/>
<b>Cc:</b> "rtk-users@public.kitware.com" <rtk-users@public.kitware.com><br/>
<b>Betreff:</b> Re: [Rtk-users] forward projectors - considering perspective view ?</div>
<div name="quoted-content">Hi,<br/>
I'm not sure I understand exactly what you mean but it seems to me<br/>
that yes, it should, i.e.<br/>
- the source position is set according to the description you have<br/>
given in your ThreeDCircularProjectionGeometry. Computation of the<br/>
source position is done in<br/>
ThreeDCircularProjectionGeometry::GetSourcePosition, you can check.<br/>
- idem for the pixel position of your detector. Computation is a bit<br/>
more subtle because it uses a matrix,<br/>
ThreeDCircularProjectionGeometry::GetProjectionCoordinatesToFixedSystemMatrix<br/>
The whole thing is for example done in rtk::JosephForwardProjectionImageFilter<br/>
Are you asking because you've observed something unexpected?<br/>
Simon<br/>
<br/>
On Tue, Jun 23, 2015 at 1:30 PM, "Robert Calließ"<br/>
<Robert.Calliess@gmx.de> wrote:<br/>
> Hello,<br/>
> I've got a questions regarding to the forward projectors for the S-ART<br/>
> reconstruction.<br/>
> Let's say there are some xray projection images from an xray machine taken<br/>
> with a circular trjectory (cone beam)<br/>
> The perspective view for these real projection images have been taken into<br/>
> account, of course.<br/>
> The forward projector creates a virtual projection image of the volume to be<br/>
> reconstructed. When this forward projection<br/>
> takes place does the forward projector also take into account the<br/>
> perspective view of the real CT system ?<br/>
><br/>
> Let's say we have a simple raycast forward projector.<br/>
> The geometry (focus, object, detector) are all given in real world units<br/>
> where the object's center is (0, 0, 0).<br/>
> By "real world units" I mean the physical dimensions from the CT system. For<br/>
> instance, if the distance between<br/>
> the object's center and the xray-source is 500mm, the the xray-source<br/>
> position is (0,0, -500.0).<br/>
><br/>
> So the virtual projection image is created as follows:<br/>
> 1: setup ray from xray-source to the current detector pixel<br/>
> 2: determine entry point and exit point of this ray with the physical<br/>
> bounding volume<br/>
> 3: sample the volume along the ray, from entry point to exit point<br/>
><br/>
> Does these steps per se include the perspective view ? Since the geomtry<br/>
> (position of focus object detector) for the reconstruction is modeled<br/>
> to imitate the real CT system's geometry, it should ?<br/>
><br/>
><br/>
><br/>
> best regards,<br/>
> Robert<br/>
><br/>
><br/>
><br/>
><br/>
><br/>
><br/>
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