[vtkusers] How to get the input to a filter as algorithm output?
Bill Lorensen
bill.lorensen at gmail.com
Tue Dec 15 11:53:52 EST 2009
After seeing Berk's reply it looks as though his
vtkImageData* inputCopy = input->NewInstance();
inputCopy->ShallowCopy(input);
blend->AddInput(inputCopy);
blend->Update();
output->ShallowCopy(blend->GetOutput());
would be:
blend->AddInput(input);
blend->Update()
this->GraftOutput(blend->GetOutput());
And here is a more complex minipipeline that implements a SobelEdgeDetector:
// Create the sobel operator
SobelOperator<OutputPixelType, ImageDimension> opers[ImageDimension];
ZeroFluxNeumannBoundaryCondition<TOutputImage> nbc;
// Setup mini-pipelines along each axis.
typename OpFilter::Pointer opFilter[ImageDimension];
typename MultFilter::Pointer multFilter[ImageDimension];
typename AddFilter::Pointer addFilter = AddFilter::New();
typename SqrtFilter::Pointer sqrtFilter = SqrtFilter::New();
for(i=0; i < ImageDimension; ++i)
{
// Create the filters for this axis.
opFilter[i] = OpFilter::New();
multFilter[i] = MultFilter::New();
// Set boundary condition and operator for this axis.
opers[i].SetDirection(i);
opers[i].CreateDirectional();
opFilter[i]->OverrideBoundaryCondition(&nbc);
opFilter[i]->SetOperator(opers[i]);
// Setup the mini-pipeline for this axis.
opFilter[i]->SetInput(this->GetInput());
multFilter[i]->SetInput1(opFilter[i]->GetOutput());
multFilter[i]->SetInput2(opFilter[i]->GetOutput());
// All axes' mini-pipelines come together in addFilter.
addFilter->SetInput(i, multFilter[i]->GetOutput());
}
// calculate the gradient magnitude
sqrtFilter->SetInput(addFilter->GetOutput());
// setup the mini-pipeline to calculate the correct regions and
// write to the appropriate bulk data block
sqrtFilter->GraftOutput( this->GetOutput() );
// execute the mini-pipeline
sqrtFilter->Update();
// graft the mini-pipeline output back onto this filter's output.
// this is needed to get the appropriate regions passed back.
this->GraftOutput(sqrtFilter->GetOutput());
On Tue, Dec 15, 2009 at 11:44 AM, Bill Lorensen <bill.lorensen at gmail.com> wrote:
> ITK has mechanisms to support minipipelines and they are used
> frequently in filters. The main facility is a Graft method that each
> DataObject implements. Filters implement GraftOutput() methods that
> Graft() a data object to a filter's output. Here is the documentation
> for an image's Graft method:
> /** Graft the data and information from one image to another. This
> * is a convenience method to setup a second image with all the meta
> * information of another image and use the same pixel
> * container. Note that this method is different than just using two
> * SmartPointers to the same image since separate DataObjects are
> * still maintained. This method is similar to
> * ImageSource::GraftOutput(). The implementation in ImageBase
> * simply calls CopyInformation() and copies the region ivars.
> * Subclasses of ImageBase are responsible for copying the pixel
> * container. */
>
> It may be an interesting future project to see if such a mechanism can
> be added to VTK.
>
> Bill
>
>
> On Tue, Dec 15, 2009 at 9:41 AM, David Gobbi <david.gobbi at gmail.com> wrote:
>> Where to start... there are a couple important items here.
>>
>> First, there's nothing wrong with directly accessing data objects when
>> you are writing a VTK filter. Obviously the filter must access the
>> data. That's completely different from accessing the data objects
>> outside of the filters, and whenever I said "don't mess with the data
>> objects", I really meant "if you want to mess with the data, then
>> write a filter".
>>
>> Second item: In VTK it isn't safe to write a VTK filter that executes
>> other VTK filters inside of it. Which is really unfortunate, because
>> it sure is a useful thing to be able to do. But if you look through
>> all the filters in VTK (i.e. vtkAlgorithm derived objects), you will
>> not find a single one that does this.
>>
>> Each vtkAlgorithm has an executive that deals with the vtkInformation
>> and sends Requests to the vtkAlgorithm. If, internally, you grab the
>> algorithm's input and feed it into your little "internal pipeline",
>> then that internal pipeline will propagate its own requests to the
>> input's producer. As a result a RequestData in the main (external)
>> pipeline can cause the internal pipeline to update, which causes all
>> sorts of requests to be sent up both the internal and external
>> pipeline before the RequestData completes. This is a violation of the
>> usual, careful way that the pipeline is supposed to step its way
>> through the various requests. It may result in undefined behavior of
>> the pipeline.
>>
>> It would be nice if someone devised a recipe for how to safely use a
>> mini-pipeline inside a VTK filter, by using deep copies of the data
>> objects or whatnot, but so far I haven't seen one. About the closest
>> thing that I've done is use ITK from inside a VTK filter.
>>
>> David
>>
>>
>> On Tue, Dec 15, 2009 at 1:18 AM, Jérôme <jerome.velut at gmail.com> wrote:
>>> Hi David D.,
>>>
>>> If I understood well, you write VTK pipeline inside a VTK filter. If so, I
>>> also do that *very* often. My way avoids to get the input data, just
>>> connects the input:
>>> blend->AddInputconnection( this->GetInputConnection( ) ); // 'this' being
>>> your vtkAlgorithm-derived filter.
>>>
>>> Secondly, I read with interest the thread in which David G. taught about VTK
>>> pipelining. And I don't think he would have your head for using the
>>> old-fashioned SetInput method. It is just like... old-fashioned, but you
>>> don't "touch" at the data. It is unfair because you add some -maybe-
>>> unuseful static cast, but the integrity of the pipeline is still preserved.
>>>
>>> David G. can you confirm my feelings?
>>>
>>> Jerome
>>>
>>> 2009/12/15 David Doria <daviddoria+vtk at gmail.com>
>>>>
>>>> The first thing I typically do (and I got this by looking at existing
>>>> filters) at the beginning of a RequestData() is:
>>>>
>>>> vtkInformation *inInfo = inputVector[0]->GetInformationObject(0);
>>>> vtkImageData *input = vtkImageData::SafeDownCast(
>>>> inInfo->Get(vtkDataObject::DATA_OBJECT()));
>>>>
>>>> However, now I have an actual object, so I have to do things like the
>>>> following:
>>>>
>>>> vtkSmartPointer<vtkImageBlend> blend =
>>>> vtkSmartPointer<vtkImageBlend>::New();
>>>> //blend->AddInputConnection(input->GetOutputPort()); //can't do this
>>>> because 'input' is not an algorithm output
>>>> blend->AddInput(input);
>>>>
>>>> David G. would have my head for this! How should this be done instead?
>>>>
>>>> Thanks,
>>>>
>>>> David D.
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>>>
>>>
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>>
>> Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html
>>
>> Please keep messages on-topic and check the VTK FAQ at: http://www.vtk.org/Wiki/VTK_FAQ
>>
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