[ITK-users] vnl matrix to numpy array gives random numbers

[Samuel Gerber]

I'd guess there is something funky going with vnl_matrix_fixed. From the
docs ( https://github.com/vxl/vxl/blob/master/core/vnl/vnl_matrix_fixed.h )
it says that the data resides on the stack. From your code snippet it is
not exactly clear to me who owns the data in fixed_matrix, probably image.
Might it be that image gets removed before you use the array view?


On Mon, Aug 7, 2017 at 10:27 PM, Nick Cullen via Insight-users <
insight-users at itk.org> wrote:

> Hi Friends !!
>
> I'm trying to use itkPyVnl directly in ITK, but I must be getting
> something wrong with pointers... The following just gives me random numbers:
>
> ```
>     typedef typename ImageType::DirectionType ImageDirectionType;
>     ImageDirectionType * direction = const_cast<ImageDirectionType *>(
> &image->GetDirection() );
>
>     typedef typename ImageDirectionType::InternalMatrixType
> DirectionInternalMatrixType;
>     DirectionInternalMatrixType * fixed_matrix = const_cast<DirectionInternalMatrixType
> *>( &direction->GetVnlMatrix() );
>
>     const vnl_matrix<double> vnlmat1 = fixed_matrix->as_matrix();
>     vnl_matrix<double> * vnlmat2 = const_cast<vnl_matrix<double> *>(
> &vnlmat1 );
>
>     typedef itk::PyVnl<double> PyVnlType;
>     PyObject * mymatrix = PyVnlType::_GetArrayViewFromVnlMatrix( vnlmat2
> );
> ```
>
> I've tried a million different things and have problems either 1) due to
> the constness of ->as_matrix() and others or 2) due to "taking the address
> of a temporary object" with ->as_matrix() ... -__-
>
>
> I know that this works:
>
> ```
>     vnl_matrix<double> * vnlmat = new vnl_matrix<double>;
>     vnlmat->set_size(2,3);
>     vnlmat->fill(0);
>     vnlmat->put(1,2,1.3);
>     vnlmat->put(1,0,2);
>     std::cout << vnlmat << std::endl;
>
>     typedef itk::PyVnl<double> PyVnlType;
>     PyObject * mymatrix = PyVnlType::_GetArrayViewFromVnlMatrix( vnlmat );
> ```
>
> Any help above is MUCH appreciated !!!!
>
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-- 
Samuel Gerber
R&D Engineer
Kitware, Inc.
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