[Insight-users] registration and spacing: GetOutput() / SetSpacing()
and const-correctness
Michael Kuhn
michakuhn at gmx . ch
Mon, 14 Jul 2003 14:01:28 -0600
Hi,
the error message I got was:
Compiling...
RegistrationTest.cxx
D:\pack\vtkMy\src\Applications\Mixed\RegistrationTest\RegistrationTest.cxx(97)
: error C2679: binary '=' : no operator defined which takes a right-hand
operand of type 'void' (or there is no acceptable conversion)
D:\pack\vtkMy\src\Applications\Mixed\RegistrationTest\RegistrationTest.cxx(213)
: see reference to function template instantiation 'void __cdecl
GetAIM(char *,class itk::SmartPointer<class itk::Image<short,3> >
*,double *)' being compiled
D:\pack\vtkMy\src\Applications\Mixed\RegistrationTest\RegistrationTest.cxx(98)
: error C2679: binary '=' : no operator defined which takes a right-hand
operand of type 'const class itk::Image<short,3> *' (or there is no
acceptable conversion)
D:\pack\vtkMy\src\Applications\Mixed\RegistrationTest\RegistrationTest.cxx(213)
: see reference to function template instantiation 'void __cdecl
GetAIM(char *,class itk::SmartPointer<class itk::Image<short,3> >
*,double *)' being compiled
Error executing cl.exe.
TestRegistrationTest.exe - 2 error(s), 0 warning(s)
The code basically looks like this:
template<typename ImageTypePointer>
void GetAIM(char* inputFilename, ImageTypePointer *img) {
(...)
vtk2itkFilter->SetInput(reader->GetOutput());
vtk2itkFilter->GetImporter()->Update();
*img = vtk2itkFilter->Update();
*img = vtk2itkFilter->GetOutput();
}
main(...) {
(...)
typedef short PixelType;
typedef itk::Image<PixelType, Dimension> ImageType;
ImageType::Pointer myImage;
(...)
GetAIM(filename, myImage);
(...)
}
Kind regards,
Michael
Luis Ibanez wrote:
>
> Hi Michael,
>
>
> GetOutput() on the VTKImageToImage filter shouldn't generate a
> compiler error. Could you please post this error message to
> the users-list ?
>
> You probably need "img" to be a
>
> "ImageTypeConstPointer * img"
>
> Instead of what you seem to be passing now:
>
> "ImageTypePointer * img"
>
>
> The reason why you don't find documentation of VTKImageToImage
> in the Doxygen pages is that this class is not officially part
> of ITK. It is just provided for convenience for exactly what
> you are using : interfacing VTK with ITK.
>
> ----
>
> Your new test is better configured, since now you are setting
> the spacing in the right place (the input images).
>
>
> The Optimizer steps are not necessarily in millimeters since
> they represent in general the parameters of any transform.
> However in the case of the Translation transform you can
> probably make this assumption safely.
>
> If the pixel spacing of your images is 0.0199, you may want to
> set the MinimumStepLength() to half of this value (e.g. your
> registration will have a precision of half a pixel), and you
> may want to set the MaximumStepLength() to 10X 0.0199, (that
> is, the first step will be ten pixels long).
>
> I'm affraid that at this point your code contains much more lines
> than what you really need for this task. I would suggest you
> to generate MetaImages from your data, and use the example in
>
>
> Insight/Examples/Registration/ImageRegistration3.cxx
>
>
> for refining your parameters.
>
> Start trying with
>
> minStepLength = 0.01
> maxStepLength = 0.20
>
> Note that the optimizer can stop due to several different
> reasons. There is a method
>
> GetStopCondition()
>
> that will tell you the reason for the optimizer to stop
>
> Valid reasons are defined in
>
> itkRegularStepGradientDescentBaseOptimizer.h
>
>
> GradientMagnitudeTolerance,
> StepTooSmall,
> ImageNotAvailable,
> SamplesNotAvailable,
> MaximumNumberOfIterations
>
>
> Call this GetStopCondition() method after the optimizer
> stops, and double check the reason for stopping.
>
>
>
> Regards,
>
>
> Luis
>
>
> ----------------------
> Michael Kuhn wrote:
>
>> Hi Luis,
>>
>> I've meanwhile rewritten the GetAIM() function. It now uses the
>> VTKImageToImage filter you've suggested. [By the way, I didn't find
>> the class in the "alphabetical list" in the html documentation
>> (http://www . itk . org/Doxygen12/html/classes . html) of itk. Is there a
>> html documentation around? I had the problem, that invoking
>> vtk2itkFilter->GetOutput() produced a compile error (probably because
>> of the "const"). I used vtk2itkFilter->GetImporter()->GetOutput()
>> instead. Everything seems to work fine, however, I'm not quite sure
>> if this is a nice solution]
>>
>> Back to my problem about spacing. Instead of adjusting the spacing of
>> my aim data inside my program, I've adjusted them outside the program
>> (i.e. using a tool which allows to adjust the aim data itself). Using
>> a spacing of 1, the registration works fine. Using a spacing of
>> 0.019998 (which is the original spacing), the registration creates a
>> start event, no iteration event, and a end event (i.e. doesn't
>> iterate). Since the length of the translation vector, the min and max
>> step size and the initial parameters have to be adjusted according to
>> the scaling (since all of them are measured in mm, aren't they?),
>> I've replaced FACTOR by a double variable factor, which is set to
>> spacing[0]. (The spacings in other directions are in about the same
>> (0.019998, 0.019998, 0.021)).
>>
>> I've attached the new code.
>>
>> Thanks a lot for your help.
>>
>> Kind regards,
>>
>> Michael
>>
>>
>>
>>
>> Luis Ibanez wrote:
>>
>>>
>>> Hi Michael,
>>>
>>>
>>> Thanks for sending your code.
>>> It helps to clarify the produre you are using.
>>>
>>>
>>> Here are some factor that can be preventing your
>>> registration process from working correctly.
>>>
>>>
>>> 1) The mechanism you are using for changing the
>>> image scale is not reliable. You are taking
>>> the output of the reader and invoking its
>>> SetSpacing() method.
>>>
>>>
>>> double spacing[2];
>>> spacing[0] = 1.0 * FACTOR;
>>> spacing[1] = 1.0 * FACTOR;
>>> reader->GetOutput()->SetSpacing(spacing);
>>> *img = reader->GetOutput();
>>>
>>>
>>> You shouldn't attempt to change the spacing
>>> of the Output() in any ITK filter, nor any
>>> other property of the filter output. The output
>>> of a filter belongs to the filter itself, and
>>> can be recomputed at any call of the Update()
>>> method. The changes of spacing that you
>>> are applying could be overriden by the next
>>> call to an Update() in the pipeline.
>>>
>>> If you double check in your GetAIM() method,
>>> you are invoking Update() on the importer,
>>> after having reset the Spacing of the reader.
>>> This Update() will override your spacing
>>> modifications.
>>>
>>>
>>> The GetOutput() method of ITK filters should
>>> infact return a ConstSmartPointer in order
>>> to prevent this miss-use of the output of a filter.
>>> This is something we may have to fix in a future
>>> release...
>>>
>>> Since you are doing this spacing change more
>>> for debugging purposes than for being part of
>>> a normal data pipeline, I'll suggest you to
>>> convert your PNG images into MetaImage format
>>> and then simply modify the spacing in the .mhd
>>> file. Then, execute your program using the .mhd
>>> files as input (instead of the PNG).
>>>
>>> Another option is to use the "ChangeInformationImageFilter"
>>> which allows you to modify image data in a pipeline
>>> compatible fashion. Note that this is a very risky
>>> operation that you would not like to have in a
>>> real medical application. Please don't use this
>>> for anything different than debugging.
>>>
>>>
>>>
>>> 2) In the conversion from VTK image to ITK image
>>> you may find convenient to use the filters:
>>>
>>> ImageToVTKImageFilter
>>> VTKImateToImageFilter
>>>
>>> available in InsightApplications/Auxiliary/vtk
>>>
>>> That will simplify the code in your GetAIM() function.
>>>
>>>
>>>
>>> 3) The only occasion in which you are entitled to call
>>> the SetSpacing() and SetOrigin() methods is when you
>>> create the image in a program, instead of reading it
>>> from a file, or taking it from the output of a filter.
>>>
>>> Filter outputs should not be modified.
>>>
>>>
>>> 4) PNG is a poor format for storing medical images.
>>> It is supported in ITK only for facilitating simple
>>> experiments, examples and demos. In real applications
>>> you may want to use a more reliable format like GIPL,
>>> Analyze, MetaImage or VTK.
>>>
>>>
>>>
>>>
>>> Regards,
>>>
>>>
>>> Luis
>>>
>>>
>
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