[Rtk-users] Fwd: About the newspacing flag

[Guangming Zang]

Hi Simon,
Thanks for your kind reply and information provided.
Basically the problem i encountered is that without changing any geometry
(i.e., sid, sdd, detector physical size), if i downsample my original
projection images, how can i reconstruct corresponding volume correctly.
In RTK, it seems that i just need to change the input projection file  and
newspacing parameter (as same as the factor of downsample), then i got
promising results. but in my own application, i simulate the situation, but
got some aliasing. So i really want to know how it work behind our RTK.
I thought that this parameter is to simulate the detector's spacing size.
And in my experiment, i set the detector physical size as 256mm*256mm, and
i got projection images P1.mha with size of 256^2 , now i downsample these
images with factor of 2( i.e., the images size change from 256^2 to 128^2
), from which i got P2.mha
in our rtkfdk, after the dowmsample. i just need change input projections
from P1.mha to P2.mha, besides, i need change flag newspacing from 1 to 2.
both of the results from RTK  are pretty good.
my questions are:
1) can i just regard the newspacing as the upsample operation with nearest
neighbor filter??
2) how many rays RTK generated in forward projecion (i.e. ray tracing part
) for each image in P2.mha??? is it 256^2????

To sum up,in my own application, can i reproduce the result from RTK for
flag "newspacing as 2"  by doing:
upsample image by factor of 2 (got a 256mm*256mm image ) and just generate
half number of rays in raytracing (forward priject ) part???

Thanks for your time and help in advance,
-Regards Guangming



On Sat, Feb 20, 2016 at 1:15 AM, Simon Rit <simon.rit at creatis.insa-lyon.fr>
wrote:

> Hi Guangming,
> The parameter is processed in rtkGgoFunctions
> <https://github.com/SimonRit/RTK/blob/master/code/rtkGgoFunctions.h>.h.
> It's passed to an itk::ChangeInformationFilter
> <http://www.itk.org/Doxygen/html/classitk_1_1ChangeInformationImageFilter.html>
> at the beginning of the rtk::ProjectionsReader.h
> <http://www.openrtk.org/Doxygen/classrtk_1_1ProjectionsReader.html>. But
> in the end, there is nothing to explain, it's simply changes the spacing of
> the input projections.
> I hope this helps,
> Simon
>
> On Fri, Feb 19, 2016 at 8:52 PM, Guangming Zang <
> guangming.zang at kaust.edu.sa> wrote:
>
>>
>> ---------- Forwarded message ----------
>> From: Guangming Zang <guangming.zang at kaust.edu.sa>
>> Date: Fri, Feb 19, 2016 at 10:49 PM
>> Subject: About the newspacing flag
>> To: rtk-users-request at public.kitware.com, Chao Wu <wuchao04 at gmail.com>,
>> Simon Rit <simon.rit at creatis.insa-lyon.fr>, "rtk-users at public.kitware.com"
>> <rtk-users at public.kitware.com>, rtk-users at openrtk.org
>>
>>
>> Dear RTK community,
>> i have a question about the parameter "newspacing " in rtkFDK and rtkSART
>> algorithm.
>> it says:--newspacing  new spacing of input projections (before
>> pre-processing).
>>  I checked in the code, and it seems not  easy to find the correct part
>> in the code about the newspacing .
>> So could anyone  help me and explain about this parameter?? i want to
>> simulate this preprocess step in my own project and compare to our RTK.
>> -best regards Guangming
>>
>> --
>> *Guangming Zang (Alex)*
>> *King Abdullah University of Science and Technology(KAUST)*
>> *University of Chinese Academy of Sciences(UCAS)*
>>
>>
>>
>>
>>
>>
>> --
>> *Guangming Zang (Alex)*
>> *King Abdullah University of Science and Technology(KAUST)*
>> *University of Chinese Academy of Sciences(UCAS)*
>>
>>
>>
>>
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>


-- 
*Guangming Zang (Alex)*
*King Abdullah University of Science and Technology(KAUST)*
*University of Chinese Academy of Sciences(UCAS)*

-- 

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