[Insight-users] forcing pipeline to update

[Jakub Bican]

Hi Karthik,

imagine, that you need 10 copies of the image rotated by increasing 
angle and fourier transformed.

Create resample filter, put in it appropriate rigid transform and 
interpolator, set the filter's input to your image (reader) and set up 
desired output parameters (spacing, origin, size). Create a fft filter 
and connect it to the output of the resample filter.

Now start a loop - in each step, set the new angle to the transform, 
update the pipeline and grab its output into your array.

In this case - setting a new angle to the transform does not force 
resample filter to recompute its output - because its parameters were 
not changed anyway and its output is still "valid". But the 
transformation inside the filter changed and re-computing leads to 
differently rotated image.

May-be, resample filter should check whether the transform was modified, 
but i don't know if it is even possible in the current ITK.

Regards,
	Jakub


Karthik Krishnan napsal(a):
> I cannot comprehend your problem. Why do you want the pipeline to update 
> if none of the parameters have changed ?
> 
> 
> Jakub Bican wrote:
> 
>>
>> Hello,
>>
>> i have a short pipeline - two filters: ResampleImageFilter followed by 
>> FFTWRealToComplexConjugateImageFilter.
>>
>> I am using it to compute different transforms of the same data:
>>
>> 1) connect the pipeline, set input to the resample filter
>> 2) loop:
>>     A) change the transform in resample filter according to the loop 
>> variable i
>>     B) set up the output parameters of resmaple filter 
>> (origin,spacing,size)
>>     C) UpdateLargestPossibleRegion() of resample filter
>>     D) UpdateLargestPossibleRegion() of fourier filter
>>     E) store the transformed data and disconnect it:
>>             transformedData[i] = fourierFilter->GetOutput();
>>             transformedData[i]->DisconnectPipeline();
>> 3) end loop
>>
>> * step C is neccessary due to some bug in fourier filter that i 
>> reported some weeks ago (otherwise fourier filter fails)
>> * step B is not usually neccessary - but sometimes i use different 
>> parameters for each transformed version
>>
>> The problem is, that if the parameters of the resample filter do not 
>> change in step B, then step C does not process anything and 
>> immediately terminates without having updated resample filter's output.
>>
>> I suppose this behavior is expectable, because resample filter has no 
>> reason to update its output ("input and any parameters else than 
>> something inside of the transform did not change"), but i need to 
>> force it to compute.
>>
> Do you mean that the transform parameters have changed and your pipeline 
> is not updating ???? Why do you need to force it to re-compute ?
> 
>> The only solution i thought of is resetting and reconnecting the 
>> pipeline, but i don't like it very much. Please, if anyone knows any 
>> clear solution how to force the filter or pipeline to update even if 
>> it is up-to-date, let me know.
>>
>> Thank you very much in advance.
>>
>> Cheers,
>>                 Jakub
>>
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> 
>