[Insight-users] coniditions on initial regiatration transform

[Karthik Krishnan]

The transform's behaviour is perfectly justified. (and you need to brush 
up your math :) )

The transform you've instantiated in that test code is a 
VersorRigid3DTransform, but the matrix you've supplied does not qualify 
as a rotation matrix. For a rotation matrix. Given a Rotation matrix R 
in column representation R = (u v w), the three column vectors are 
mutually orthogonal,
ie: u x v = w; v x w = u; w x u = v;

Rick Shilling wrote:

> Hi Karthik-
>
> Attached is the source file (75 lines of code) that demonstrates the 
> stated problem. You'll have to un/comment the two different matrices 
> if you want to run it. In debug mode, when I stepped into
>
> MatrixOffsetTransformBase<TScalarType, NInputDimensions, 
> NOutputDimensions>
> ::TransformPoint(const InputPointType &point) const
> {
> return m_Matrix * point + m_Offset;
> }
>
> with
> matrix[0][0]=0; matrix[0][1]=0; matrix[0][2]=-1; offset[0]=10;
> matrix[1][0]=0; matrix[1][1]=1; matrix[1][2]=0; offset[1]=20;
> matrix[2][0]=-1; matrix[2][1]=0; matrix[2][2]=0; offset[2]=30;

Replace this matrix with :

matrix[0][0]=0; matrix[0][1]=0; matrix[0][2]=+1; offset[0]=10;
matrix[1][0]=0; matrix[1][1]=1; matrix[1][2]=0; offset[1]=20;
matrix[2][0]=-1; matrix[2][1]=0; matrix[2][2]=0; offset[2]=30;

and you won't have that error.

------

SetMatrix is a dangerous call for users using the 
VersorRigid3DTransform, you would be better off with initializing a 
versor and setting that versor on the transform.

HTH
-karthik

>
> m_Matrix is the identity while the other matrix assignment (commented 
> out) gives m_Matrix the value assigned. I ran it on VC++6.0. Let me 
> know if you run the code & get the same result. Thanks.
>
> Rick
>
> */Karthik Krishnan <Karthik.Krishnan at kitware.com>/* wrote:
>
>     On Fri, 2006-06-23 at 13:15 -0700, Rick Shilling wrote:
>     > In itk registration , I provide an initial rigid transformation with
>     > rotation in the itk registration object:
>     >
>     > 0 0 -1
>     > 0 1 0
>     > -1 0 0
>     >
>     > and offset:
>     > 230
>     > -110
>     > 331
>     >
>     > I noticed that in MatrixOffsetTransformBase class when its
>     > transforming points:
>     >
>     > MatrixOffsetTransformBase
>     > NOutputDimensions>
>     > ::TransformPoint(const InputPointType &point) const
>     > {
>     > return m_Matrix * point + m_Offset;
>     > }
>     >
>     > m_Matrix is the indentity & not what was provided for in:
>     >
>     > transform->SetMatrix(matrix);
>     >
>     > Other times m_matrix uses the right values yet there is no
>     difference
>     > in code between the two cases. Is there any precondition on the
>     > rotation matrix that is imposed by the registration process that
>     > changes it the transform to the identity? Thanks.
>
>     Can you write a minimal test to prove that ?
>
>     >
>     > Rick
>     >
>     >
>     >
>     >
>     >
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