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Hello Simon,</div>
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I realize that a 90° scan only allows for a partial reconstruction of the volume. This approach seems to be quite common in industrial applications due to space and time constraints, but I have not found much information about it in the literature.</div>
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The Astra toolbox's FDK implementation seems to cope with this quite well, at least in the center of the volume.</div>
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The rescaled pixel size should be 6 * 0.099 mm = 0.594 mm.</div>
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Best regards,</div>
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Christian</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>Von:</b> Simon Rit <simon.rit@creatis.insa-lyon.fr><br>
<b>Gesendet:</b> Sonntag, 2. Juni 2024 08:00<br>
<b>An:</b> Christian Riesch <christian.riesch@live.com><br>
<b>Cc:</b> rtk-users@openrtk.org <rtk-users@openrtk.org><br>
<b>Betreff:</b> Re: [Rtk-users] Reconstruction geometry</font>
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<div>Hi Christian,</div>
<div>Thanks for the share. It was not clear to me that you had a 90° scan sorry. FDK is not appropriate for such a 90° scan, it's meant for a full 360° scan. rtkfdk tries to apply a short scan but Parker weighting is for 180°+fan-angle. So I'm not sure what
to expect from FDK with such a scan.<br>
</div>
<div>The projections that you shared are 512x511, can you please clarify the pixel size? I would try iterative reconstruction with such a scan.</div>
<div>Cheers,</div>
<div>Simon<br>
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<div dir="ltr" class="x_gmail_attr">On Fri, May 31, 2024 at 12:25 PM Christian Riesch <<a href="mailto:christian.riesch@live.com">christian.riesch@live.com</a>> wrote:<br>
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Hello Simon,</div>
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Thanks for the quick response.</div>
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So I have tried rtksimulatedgeometry with --arc 273 together with adding --neworigin=-153.5985,-153.2025,0 to rtkfdk.</div>
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The result is different than before, but still looks very wrong (two ribbons and some vertical lines).</div>
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I may be able to share some data later.</div>
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Best regards,</div>
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Christian</div>
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<div id="x_m_5972968796847892275divRplyFwdMsg" dir="ltr"><span style="font-family:Calibri,sans-serif; font-size:11pt; color:rgb(0,0,0)"><b>Von:</b> Simon Rit <<a href="mailto:simon.rit@creatis.insa-lyon.fr" target="_blank">simon.rit@creatis.insa-lyon.fr</a>><br>
<b>Gesendet:</b> Donnerstag, 30. Mai 2024 08:48<br>
<b>An:</b> Christian Riesch <<a href="mailto:christian.riesch@live.com" target="_blank">christian.riesch@live.com</a>><br>
<b>Cc:</b> <a href="mailto:rtk-users@openrtk.org" target="_blank">rtk-users@openrtk.org</a> <<a href="mailto:rtk-users@openrtk.org" target="_blank">rtk-users@openrtk.org</a>><br>
<b>Betreff:</b> Re: [Rtk-users] Reconstruction geometry</span>
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<div style="direction:ltr">Hi,</div>
<div style="direction:ltr">I can see two problems:</div>
<div style="direction:ltr">- you need to indicate the short scan to rtksimulatedgeometry, e.g. --arc 273 or, if the angle convention is opposite in your system, --arc -273. You may have to tune the --first_angle option to position the volume as you wish but
that should not prevent accurate reconstruction.</div>
<div style="direction:ltr">- you need to center your projections, i.e., add the option --neworigin=-153.5985,-153.2025,0 to rtkfdk, computed with -0.5*(3104-1)*0.099 and -0.5*(3096-1)*0.099.</div>
<div style="direction:ltr">Don't hesitate to share a dataset if that does not help.</div>
<div style="direction:ltr">Good luck!</div>
<div style="direction:ltr">Simon</div>
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<div style="direction:ltr">On Thu, May 30, 2024 at 6:58 AM Christian Riesch <<a href="mailto:christian.riesch@live.com" id="x_m_5972968796847892275OWAce49ae47-c33d-4707-5d97-0b1b5b798a8c" target="_blank">christian.riesch@live.com</a>> wrote:</div>
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<p>Hello,</p>
<p> </p>
<p>I'm currently trying to use RTK for a reconstruction from a stack of images that resulted from a 90° scan, but struggling to get the parameters right.</p>
<p>On the other hand, I was able to get what looks like a faithful reconstruction using the Astra toolbox and the script from
<a href="https://tomroelandts.com/articles/astra-toolbox-tutorial-reconstruction-from-projection-images-part-1" id="x_m_5972968796847892275OWA541d403d-3e31-4fc9-218d-6dd000ba5aa6" target="_blank" style="margin-top:0px; margin-bottom:0px">
https://tomroelandts.com/articles/astra-toolbox-tutorial-reconstruction-from-projection-images-part-1</a></p>
<p> </p>
<p>I have these parameters from the X-ray device that captured the images (size 3104x3096):</p>
<p> "fod_mm": 75.46, (focus to object distance)</p>
<p> "odd_mm": 407.07, (object to detector distance)</p>
<p> "pixel_size_mm": 0.099,</p>
<p> "start_arc_deg": 45.0,</p>
<p> "stop_arc_deg": -45.0</p>
<p>(There is also "detector_offset_mm": 9.8, which I have ignored so far with both Astra and RTK.)</p>
<p> </p>
<p>So I have tried to create a geometry using</p>
<p>.\rtksimulatedgeometry.exe -o"geo.xml" -n91 -f45 -a90 --sdd=482.53 --sid=75.46</p>
<p>where sdd = fod_mm + odd_mm and sid = fod_mm,</p>
<p>and a reconstruction with</p>
<p>.\rtkfdk.exe -p"images" -r".*tif" -g"geo.xml" -o"out.tif" --dimension=512,512,200 --newspacing=0.099</p>
<p> </p>
<p>However, out.tif contains mostly zeros and a weird ribbon-like shape in the center. So I think my geometry is wrong, but I don't know how to fix it.</p>
<p> </p>
<p>For comparison, here are the input parameters for the Astra script:</p>
<p>distance_source_origin = 75.46 # [mm]</p>
<p>distance_origin_detector = 407.07 # [mm]</p>
<p>detector_pixel_size = 0.099 # [mm]</p>
<p>num_projections = 91</p>
<p>start_angle_deg = 45</p>
<p>stop_angle_deg = 135</p>
<p> </p>
<p>Any pointers would be appreciated.</p>
<p> </p>
<p>Best regards,</p>
<p>Christian Riesch</p>
<p> </p>
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