[Rtk-users] Gantry rotation direction and artefacts

[Simon Rit]

Thanks for the illustration. Maybe the detector is not oriented as intended
by RTK? If you look at the first drawing of the geometry doc
<http://www.openrtk.org/Doxygen/DocGeo3D.html>, I would question the
direction of the vector v. You can probably just flip it to put it in the
right direction? e.g. with
rtkfdk -p . -r ^proj.mha$ -g direct.xml --spacing 0.5 -d 300 --hardware
cuda -o fdk.mha --newdirection 1,0,0,0,-1,0,0,0,1 --neworigin -140,151.6,0
which comes down to flipping the y axis after reconstruction without the
last two options. I think that the RTK coordinate system becomes indirect
if you flip this v axis which is probably ignored by your visualization
tool. I admit I realized only recently that I often reconstruct data which
are like this.
I hope I'm clear, if not that's probably because I don't master so well all
this...
Simon

On Fri, Aug 28, 2020 at 1:23 PM Vincent Libertiaux <vl at xris.eu> wrote:

> Hi Simon,
>
> I am afraid I was no clear enough. Please find a picture of the real
> object and the reko at that link:
>
> https://www.dropbox.com/sh/ul0oy9kv3us4ey7/AABQ5Y4R1PR-jcRawGFKOUK4a?dl=0
>
>
> So you can see that on the part, the serial number is on the "head" side
> while it is on the "tail" side on the reconstruction, using the "direct"
> geometry.  That is what I call the mirror image.  The rotation axis is
> along the vertical direction of the image.  I could easily reorder the
> reconstructed slice to get it in the right orientation, but I was wondering
> where the issue comes from.
>
> Best regards,
> Vincent
>
> On 28.08.20 12:13, Simon Rit wrote:
>
> Mirror in which direction? Depending on the direction, it can also be a
> 180° offset of the angle. If it reconstructs well, I would assume that the
> direct direction is the correct one but there is something else you need to
> understand...
>
> On Fri, Aug 28, 2020 at 10:44 AM Vincent Libertiaux <vl at xris.eu> wrote:
>
>> Hi Simon,
>>
>> thank you for testing my dataset.
>>
>> I get the same results you describe and I am quite happy with the first
>> result. However, the reconstructed volume is a "mirror" view of the real
>> object, and my guess was that the rotating plate was going in the opposite
>> direction assumed by rtk. Is it the wrong assumption?
>>
>> Thank you again for your help,
>>
>> best regards,
>>
>> Vincent
>>
>>
>> Thanks for the dataset. When I run
>>   rtkfdk -p . -r ^proj.mha$ -g direct.xml --spacing 0.5 -d 300 --hardware
>> cuda -o fdk.mha
>> The result looks good to me. Obviously, when I run
>>   rtkfdk -p . -r ^proj.mha$ -g inverse.xml --spacing 0.5 -d 300
>> --hardware cuda -o fdk.mha
>> the result is bad since the correct rotation direction seems to be the
>> direct one. Did you expect the second line to produce the correct result?
>> Or is the first line not producing a good enough result in your opinion?
>>
>
>
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