[vtkusers] vtkTransform question

[David Gobbi]

Hi Kiran,

The order in which you apply rotations is important.

If you get the angles like this:

 xa,ya,za = transform.GetOrientation()

then to rebuild the matrix you have to do this, assuming that
the transform is in PreMultiply mode:

 transform.RotateZ(za)
 transform.RotateX(xa)
 transform.RotateY(ya)

In VTK the 'orientation' is described by a rotation around the y axis,
followed by a rotation around the x axis, followed by a rotation around
the z axis.

My advice: whenever possible, avoid using angles to describe
rotations.  If you can solve your problem completely with linear
algebra without resorting to trigonometry, the solution will
usually be much more elegant.

 - David

--
  David Gobbi, MSc                       dgobbi at irus.rri.ca
  Advanced Imaging Research Group
  Robarts Research Institute, University of Western Ontario

On Mon, 15 Oct 2001, Kiran, P (CORP, GEITC) wrote:

>
> Hi all:
>
> I tried to test "GetOrientation()" method of vtkTranform as following:
>
> 1) set the vtkMatrix4x4
> 2) set the matrix in step as input to vtkTransform's SetMatrix method
> 3) get the orientation matrix using Getorientation() method.
>
> These are results:
> I set the input 4x4 matrix for vtkTransform as: (  using SetMatrix() method)
>    0.999245	 -0.0173388   0.0347622   0 ;
>    0.0124273       0.990517     0.136826     0;
>    0.036805        0.136291     -0.989985    0;
>    0                        0                0                1;
> and I got the orientation as:  {7.83328, -177.871, -1.00284}
>
> I just want to know the reverse process is correct or not, so  I tried the
> following:
> 1)  Set this orienataion matrix as input to vtkTransform ( using
> RotateX(),RotateY(),RotateZ() methods )
> 2) Get the 4x4 Matrix, which is a result of this orienatation.
>
> The resulting 4x4 matrix is:
>       -0.999157     -0.01749   -0.0371516    0 ;
>       -0.0224014    0.990428  0.136197      0 ;
>       0.0344139     0.136914   -0.989985    0 ;
>       0                     0               0                1 ;
>
> There are some small discrepancies in the signs of the input and output
> matrices.
> Can someone, through some light on this.
> I am including the test file as an attachment.
>
> Thanks
> Kiran
> ----------------------------------------------------attachment--------------
> --------------------------------------------------------
>
>  <<test_vtkTransform.cxx>>
>
>
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