[Rtk-users] Issue report regarding the recorder of Time elapsed

[Simon Rit]

I can try. Forward and back projection have the same algorithmic
complexity but voxel based backprojection benefits from several
optimizations in terms of memory management and computations that
makes it faster. The best is to look at the code for further
details... although both have far from being optimal. And I did not
get the sentence "the backprojection should take much longer time than
sart algorithm." because SART contains a backprojection and other
steps so SART is obviously longer than the bp alone.
Your log is strange and I don't see what steps are not timed that
would take most of the time. I did the same test on my computer and
here is my result:

OS-SR-466:tmp srit$ rtksimulatedgeometry -n 360 -o geo
OS-SR-466:tmp srit$ rtkprojectshepploganphantom -g geo -o proj.mha
--dimension 512
OS-SR-466:tmp srit$ rtksart  -p . -r proj.mha  -g geo -o SART_SL3.mha
 -f Joseph -b VoxelBasedBackProjection --newspacing 0.5  --dimension
128,128,128  --spacing 1,1,1  --origin -64,-64,-64 -l 0.5 -n 3  --time
1
Recording elapsed time...
SARTConeBeamReconstructionFilter timing:
  Extraction of projection sub-stacks: 0.288571 s
  Multiplication by zero: 0.131672 s
  Forward projection: 34.3612 s
  Subtraction: 0.203409 s
  Multiplication by lambda: 0.146459 s
  Ray box intersection: 1.30755 s
  Division: 0.187294 s
  Multiplication by the gating weights: 0 s
  Displaced detector: 0.278408 s
  Back projection: 11.8456 s
  Volume update: 0 s
It took...  53.2765 s

Simon

On Mon, Jul 27, 2015 at 10:41 AM, Guangming Zang
<guangming.zang at kaust.edu.sa> wrote:
> Hi Simon,
> Thanks for your reply.
> would you pls help and explain why backprojection is expected to take
> shorter time than forward projection?? because i was thinking if no caching
> step, the backprojection should take much longer time than sart algorithm.
> yes, i run rtksart for 2 times once.it took 12xxs, similar to the time
> consumed of 3 times's sart, which much slower than my own application.
> BTW, D drive is local disk drive, and 360pro_SL_Vol128_512.mha are 360
> shapp-logan projections(512*512 resolution each)
> rtksart  -p . -r 360pro_SL_Vol128_512.mha  -g geometry.xml -o
> ../Result_SL512/SART_SL3.mha   -f Joseph -b VoxelBasedBackProjection
> --newspacing 0.5  --dimension 128,128,128  --spacing 1,1,1  --origin
> -64,-64,-64 -l 0.5 -n 3  --time 1
>
> and i will try reader->Update() like what you said.
> Thanks
> Guangming
>
>
>
> Guangming Zang (Alex)
> King Abdullah University of Science and Technology(KAUST)
> University of Chinese Academy of Sciences(UCAS)
>
>
>
>
> 2015-07-27 8:59 GMT+03:00 Simon Rit <simon.rit at creatis.insa-lyon.fr>:
>>
>> Hi Guangming,
>> It's not surprising to me that the backprojection is faster than the
>> forward projection, that's what I expect. If the total time is longer,
>> that's probably that some individual steps are not included in the total
>> time. Can you try to add
>> reader->Update();
>> before the line
>>
>> itk::TimeProbe totalTimeProbe;
>>
>> in rtksart.cxx? It may be that all the reading operations are done but not
>> timed in the sart->Update(). Why they are so long, I don't know, is your D:
>> drive a network drive? Do you observe the same behavior if you do rtksart 2
>> times in a row?
>>
>> Simon
>>
>>
>>
>> On Mon, Jul 27, 2015 at 12:30 AM, Guangming Zang
>> <guangming.zang at kaust.edu.sa> wrote:
>>>
>>> Hi RTK community,
>>> i am using SART algorithm to reconstruct an object.
>>> But in this new RTK version, the time recording seems a little weird:
>>>  the total time is 1219.12s , but adding the time cost in different
>>> stages is not 1291.12 s. especially for "backprojection" part, only 16.6051s
>>> to reconstruct a 128^3 volume ?? even shorter than forward projection part.
>>> BTW, the -f and -b are Joseph and VoxelBasedBackProjection, respectively,
>>> both multi-threading  i think.
>>> Can anyone tell me what's going on?
>>> Thanks
>>> Regards
>>> Guangming
>>>
>>>
>>> Guangming Zang (Alex)
>>> King Abdullah University of Science and Technology(KAUST)
>>> University of Chinese Academy of Sciences(UCAS)
>>>
>>>
>>>
>>>
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>>
>
>
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