[Insight-users] setOffset vs setTranslation

[Dan Mueller]

Hi Patrick,

Please see the documentation in Code/Common/itkMatrixOffsetTransformBase.h

/** Set offset (origin) of an MatrixOffset TransformBase.
   *
   * This method sets the offset of an MatrixOffsetTransformBase to a
   * value specified by the user.
   * This updates Translation wrt current center.  See the warning regarding
   * offset-versus-translation in the documentation for SetCenter.
   * To define an affine transform, you must set the matrix,
   * center, and translation OR the matrix and offset */
  void SetOffset(const OutputVectorType &offset)

  /** Set center of rotation of an MatrixOffsetTransformBase
   *
   * This method sets the center of rotation of an MatrixOffsetTransformBase
   * to a fixed point - for most transforms derived from this class,
   * this point is not a "parameter" of the transform - the exception is that
   * "centered" transforms have center as a parameter during optimization.
   *
   * This method updates offset wrt to current translation and matrix.
   * That is, changing the center changes the transform!
   *
   * WARNING: When using the Center, we strongly recommend only changing the
   * matrix and translation to define a transform.   Changing a transform's
   * center, changes the mapping between spaces - specifically, translation is
   * not changed with respect to that new center, and so the offset is updated
   * to * maintain the consistency with translation.   If a center is not used,
   * or is set before the matrix and the offset, then it is safe to change the
   * offset directly.
   *        As a rule of thumb, if you wish to set the center explicitly, set
   * before Offset computations are done.
   *
   * To define an affine transform, you must set the matrix,
   * center, and translation OR the matrix and offset */
  void SetCenter(const InputPointType & center)

  /** Set translation of an MatrixOffsetTransformBase
   *
   * This method sets the translation of an MatrixOffsetTransformBase.
   * This updates Offset to reflect current translation.
   * To define an affine transform, you must set the matrix,
   * center, and translation OR the matrix and offset */
  void SetTranslation(const OutputVectorType & translation)

Hope this helps.

Cheers, Dan

2009/9/25 Patrik Brynolfsson <patrik.brynolfsson at radfys.umu.se>:
> I just have a quick question; what is the difference between the
> setTranslation and setOffset methods for e.g. the VersorRigid3DTransform?
>
> --
> Patrik Brynolfsson