On 25.04.22 09:07, Simon Rit wrote:
Hi Vincent (and Jasper),
I agree with Jasper that this is most likely due to a difference in
geometric calibration between the two datasets. Do you have more
information on what does B use (projection matrices, detailed
parametrization, etc.)? I think that such a blur can be caused by a
difference in source to detector distance (or, equivalently, detector
pixel size).
Simon
On Tue, Apr 19, 2022 at 11:08 AM Vincent Libertiaux <v...@xris.eu> wrote:
On 16.04.22 13:52, Jasper Albertus Nijkamp wrote:
> Hi Vincent,
>
> From just these two images, it is a bit hard to help. However,
I have seen similar challenges when the detector vertical offset
is not properly set. If you could share a bit more data (fx
projection data and the geometry), more people might be able to help.
>
> Jasper
>
> -----Original Message-----
> From: Rtk-users <rtk-users-boun...@public.kitware.com> On Behalf
Of Vincent Libertiaux
> Sent: Friday, 15 April 2022 17:15
> To: rtk-users <rtk-users@public.kitware.com>
> Cc: Damien Koch <d...@xris.eu>
> Subject: [Rtk-users] Lateral blur in a FDK reconstructed volume
>
> Hello rtk users !
>
> I am facing a problem for which I have exhausted all the
possibilities except asking you.
> I have performed a standard FDK reconstruction of a lego bricks
assembly. I used a custom-made code to compute the detector
horizontal offset and tilt angle, found to be 1.15 mm and 0.02°
respectively. The result of the reconstruction is shown in the
picture
> https://ibb.co/LdMzJF2 . The volume looks mostly sharp, except
on the lateral edges, let's say on the last half brick.
>
> We had the opportunity to have the same volume reconstructed
with two commercial solutions. The first one, "A", produced the
same results than rtk. The second, "B", produced the result shown
in the picture https://ibb.co/VwXMmRH
>
> In this case, the edges are sharp too. The offset values found
with this software were very close (1.13mm and 0.025°
respectively) and feeding them to rtksimulatedgeometry didn't
change my result. No other correction was allegedly applied.
>
> I thought that the edge blurring was due to a wobbling artefact
but it can't be the case according to the result with the "B"
software.
>
> Do you have any idea on what could cause this blurring on the
edges ?
>
> I thank you very much for any clue.
>
> Best regards,
>
> Vincent
>
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Hi Jasper,
thank you for your reply. I had already tried to play with the
vertical
offset but setting it to a value different than 0 progressively
decrease
the overall quality of the reconstruction.
Following your advice, here are the projections:
http://share.xris.eu/d91b09673bba
word of warning, the set is very large (900 projections on a
3072x3072
pixels detector, approx. size = 16Go) I could try and make it
smaller
by downsampling it but I am afraid it would mask the problem. I
can try
and do it on request.
The geometric parameters I used were: SDD = 810 mm, SID = 410 mm,
proj_iso_x = 1.15mm and in_angle = 0.02°.
Best regards,
Vincent
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Hi Simon, hi Jasper.
I have investigated a bit more on that issue. I told you in my first
message that both software we used besides rtk found the same set of
parameters. After playing a bit more with the software "B" (the one
that gives the sharp edges), I found out that the tilt angle is found to
be 0 and it is the out-of-plane angle around the vertical axis of the
detector which is non zero (and very coincidentally is very close to the
tilt angle we computed). The value is quite low (0.025°). I am a bit
puzzled as, if I am not mistaken, the literature always assumes that
both out of plane angles are negligible as long as they don't come close
2°. We are two order of magnitude below this value, hence my surprise.
I am also wondering if this angle can be introduced in the rtk
geometry. From the doc (http://www.openrtk.org/Doxygen/DocGeo3D.html),
it seems that only the out-of-plane angle around the detector horizontal
axis is considered. Is that correct ? If yes, is there a way to model
the other one with the available parameters ?
Once again, thank you for any help you can provide.
Kindest regards,
Vincent
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