[Insight-users] Inverse Transform doesn't not catch singular matrices

[Bill Lorensen]

Francois,

Please submit a bug. Include the contents of your posting plus any other
helpful info.

http://itk.org/Wiki/ITK_Procedure_for_Contributing_Bug_Fixes

Thanks,

Bill

On Fri, Feb 8, 2008 at 4:02 PM, Francois Budin <
insight.mailinglist.francois at budin.fr> wrote:

> Hi all,
>
> I was trying to compute the inverse of an affine transform (
> itk::AffineTransform<double,3> ) using the following function:
> bool GetInverse (Self *inverse) const
>
> I couldn't succeed to detect when the matrix was non-invertible. I
> tried to verify the value returned in the boolean but it always seems
> to be 1. I also tried to detect if any exception were thrown but it
> didn't catch anything.
> My code is the following:
>
>
>    bool noninvertible=0;
>    itk::Transform<double,3,3>::Pointer inverseTransform;
>    try
>    {
>     typename AffineTransformType::Pointer affine =
> dynamic_cast<AffineTransformType* > ( transform.GetPointer() ) ;
>    if(affine )
>    {
>      typename AffineTransformType::Pointer
> affinetemp=AffineTransformType::New();
>      std::cout<<affine->GetInverse(affinetemp)<<std::endl;//should
> print 0 if non-invertible transform;
>      inverseTransform=affinetemp;
>    }
>  else
>    {
>      typename RotationType::Pointer rigid =
> dynamic_cast<RotationType* > ( transform.GetPointer() ) ;
>      if(rigid)
>      {
>        typename RotationType::Pointer rigidtemp=RotationType::New();
>        std::cout<<rigid->GetInverse(rigidtemp)<<std::endl;
>        inverseTransform=rigidtemp;
>      }
>      else
>      {
>        noninvertible=1;//I don't need to handle the other kinds of
> transform
>      }
>    }
>    }
>    catch(...)
>    {
>      std::cout<<"Exception Detected"<<std::endl;
>    noninvertible=1;
>    }
>
>
> Then I tried to write a small piece of code which copies what ITK is
> doing to inverse an affine transform to test the inversion of the
> matrix itself:
>
> #include <itkMatrix.h>
>
> int main(int argnb,char* arg[])
> {
> itk::Matrix<double,3,3> mat;
> mat.Fill(0);
> mat[0][0]=-1;
> try
>      {
>     std::cout<<mat.GetInverse()<<std::endl;
>      }
>    catch(...)
>      {
>      std::cout<<"Singular"<<std::endl;
>      }
>
> return 0;
> }
>
> Nothing got caught, so I suspect that there is a problem somewhere and
> that the vnl functions used to inverse the matrix does not throw any
> exception when it is singular. If I am wrong, could anybody tell me
> what I should change in my code?
> Sincerely,
>
> Francois
> _______________________________________________
> Insight-users mailing list
> Insight-users at itk.org
> http://www.itk.org/mailman/listinfo/insight-users
>
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