[Insight-users] itkMatrix error: discards qualifiers??

[michiel mentink]

thank you, that works indeed.

cheers, Michael


On Tue, Mar 30, 2010 at 3:31 PM, Luis Ibanez <luis.ibanez at kitware.com>wrote:

> Hi Michiel,
>
> You don't need to get that direction matrix as a reference.
>
> If you get it as a copy, things should go smoothly and
> the compiler should be happy.
>
>
> Instead of:
>
>   const ImageType::DirectionType & direction = image->GetDirection();
>
> you need to do:
>
>   ImageType::DirectionType   direction = image->GetDirection();
>
> then you modify "direction", to apply your rotation,
> and when you are done,
> you set it back to the image by calling:
>
>             image->SetDirection(   direction  );
>
>
>
>    Regards,
>
>
>         Luis
>
>
> -------------------------------------------------------------------------------
> On Tue, Mar 30, 2010 at 6:14 AM, michiel mentink
> <michael.mentink at st-hughs.ox.ac.uk> wrote:
> > Dear Luis,
> >
> > thank you for your reply, now I understand what is meant!
> >
> > Direction is from an image:
> >
> >   const ImageType::DirectionType & direction = image->GetDirection();
> >
> > I'm trying to rotate the image by just changing the direction matrix of
> the
> > image.
> >
> > Unfortunately, when I just leave out 'const' from that line, the compiler
> > complains
> > that it's not the same type as expected.
> >
> > Maybe I should just create a new matrix, copy the value of
> > image->GetDirection()
> > into it, apply the rotation, and use image->SetDirection()?
> >
> > cheers, Michael
> >
> >
> > On Mon, Mar 29, 2010 at 11:04 PM, Luis Ibanez <luis.ibanez at kitware.com>
> > wrote:
> >>
> >> Hi Michiel,
> >>
> >>
> >> It is excellent that you are diving into the code
> >> looking for deeper understanding !
> >>
> >>
> >> The message that you get indicates that you are
> >> attempting to change the value of a variable that
> >> has been declared "const" previously.
> >>
> >> The "const" declaration is a promise made to the
> >> compiler, stating that you will not change the value
> >> of that variable.
> >>
> >> When the compiler catch you breaking that promise,
> >> it get angry at you and gives you the error message:
> >>
> >> "error: passing ‘const   X to  Z discards qualifiers"
> >>
> >>
> >> Where the "qualifier" refers to the "const" property
> >> of that variable.
> >>
> >>
> >> The error message indicates that you are calling
> >> the operator=() method on a const matrix (as left
> >> argument of the = ).
> >>
> >>
> >> You did so, with an expression such as:
> >>
> >>
> >>  const MatrixType  myConstMatrixThatWillNeverChange;
> >>
> >>  myConstMatrixThatWillNeverChange = anotherMatrix;
> >>
> >>
> >> This may also happens implicitly if the matrix
> >> happens to be a member variable of a class,
> >> and you attempt to do such assignment inside
> >> a "const" method of the class.
> >>
> >>
> >> If you share with use the exact declaration of your
> >> "direction" matrix we could tell you more about how
> >> to get around the problem.
> >>
> >>
> >>       Regards,
> >>
> >>
> >>             Luis
> >>
> >>
> >>
> >>
> --------------------------------------------------------------------------
> >> On Mon, Mar 29, 2010 at 12:01 PM, michiel mentink
> >> <michael.mentink at st-hughs.ox.ac.uk> wrote:
> >> >
> >> > In an autodidactic effort, I'm trying to rotate an image by 'hand', by
> >> > multiplying the 'direction' matrix of an image by a rotation matrix.
> >> >
> >> > To do that, I'm copying bits out of itkEuler3DTransform.txx
> >> > In that file, a RotationX matrix is defined:
> >> >
> >> > Matrix<TScalarType,3,3> RotationX
> >> >
> >> > However, when I try doing that, I'm getting the following error:
> >> >
> >> > error: passing ‘const itk::Matrix<double, 3u, 3u>’ as ‘this’ argument
> of
> >> > ‘const itk::Matrix<T, NRows, NColumns>& itk::Matrix<T, NRows,
> >> > NColumns>::operator=(const itk::Matrix<T, NRows, NColumns>&) [with T =
> >> > double, unsigned int NRows = 3u, unsigned int NColumns = 3u]’ discards
> >> > qualifiers
> >> >
> >> > 1) What does this mean?
> >> > 2) How do I get my beloved Matrix?
> >> >
> >> > #include <itkMatrix.h>
> >> > #include <vnl/vnl_matrix.h>
> >> >
> >> >   typedef itk::Matrix<double,3,3> Matrix;
> >> >
> >> >   Matrix RotationX;
> >> >  // ImageType::DirectionType RotationX;
> >> >
> >> > //  vnl_matrix_fixed<double,3,3> RotationX;
> >> >
> >> >   RotationX[0][0] = 1; RotationX[0][1] =   0; RotationX[0][2] = 0;
> >> >   RotationX[1][0] = 0; RotationX[1][1] =  cx; RotationX[1][2] = sx;
> >> >   RotationX[2][0] = 0; RotationX[2][1] = -sx; RotationX[2][2] = cx;
> >> >
> >> >   direction = direction*RotationX;
> >> >
> >> > cheers,
> >> >
> >> > Michael
> >> >
> >> >
> >> >
> >> >
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