<html><head></head><body><div style="font-family: Verdana;font-size: 12.0px;"><div>
<div>Hello,</div>
<div>thank you for the answer. I wanted to get a short feedback to the last part of my email.</div>
<div>I guess I missed the "?" .</div>
<div> </div>
<div>> Hello Simon,<br/>
> thank you for your fast reply. It was a question in general.<br/>
> I had a look at the ThreeDCircularProjectionGeometry file. But generally<br/>
> it should be the same as I described in my email. Also for the<br/>
> joseph projector, spanning the ray from source to detector position (pixel).<br/>
> This automatically gives divergent rays. ??</div>
<div>??</div>
<div> </div>
<div>best regards,</div>
<div>Robert</div>
<div>
<div name="quote" style="margin:10px 5px 5px 10px; padding: 10px 0 10px 10px; border-left:2px solid #C3D9E5; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">
<div style="margin:0 0 10px 0;"><b>Gesendet:</b> Dienstag, 23. Juni 2015 um 15:08 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">No, the isocenter is the center of rotation which is also used as the<br/>
origin of the coordinate system of the tomography in RTK.<br/>
Simon<br/>
<br/>
On Tue, Jun 23, 2015 at 3:04 PM, "Robert Calließ"<br/>
<Robert.Calliess@gmx.de> wrote:<br/>
> Hello Simon,<br/>
> thank you for your fast reply. It was a question in general.<br/>
> I had a look at the ThreeDCircularProjectionGeometry file. But generally<br/>
> it should be the same as I described in my email. Also for the<br/>
> joseph projector, spanning the ray from source to detector position (pixel).<br/>
> This automatically gives divergent rays.<br/>
><br/>
> I have another question. Is the isocenter the center of the object ?<br/>
><br/>
> best regards,<br/>
> Robert<br/>
><br/>
> Gesendet: Dienstag, 23. Juni 2015 um 14:00 Uhr<br/>
> Von: "Simon Rit" <simon.rit@creatis.insa-lyon.fr><br/>
> An: "Robert Calließ" <Robert.Calliess@gmx.de><br/>
> Cc: "rtk-users@public.kitware.com" <rtk-users@public.kitware.com><br/>
> Betreff: Re: [Rtk-users] forward projectors - considering perspective view ?<br/>
> 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<br/>
> 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<br/>
>> 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.<br/>
>> 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/>
>> _______________________________________________<br/>
>> Rtk-users mailing list<br/>
>> Rtk-users@public.kitware.com<br/>
>> <a href="http://public.kitware.com/mailman/listinfo/rtk-users" target="_blank">http://public.kitware.com/mailman/listinfo/rtk-users</a><br/>
>><br/>
><br/>
> _______________________________________________<br/>
> Rtk-users mailing list<br/>
> Rtk-users@public.kitware.com<br/>
> <a href="http://public.kitware.com/mailman/listinfo/rtk-users" target="_blank">http://public.kitware.com/mailman/listinfo/rtk-users</a><br/>
></div>
</div>
</div>
</div></div></body></html>