[vtkusers] automatic update of objects generating a vtkAbstractTransform

David Gobbi dgobbi at irus.rri.on.ca
Tue Mar 20 20:24:15 EST 2001

Hi Alexandre,

There is an automatic update mechanism for vtkAbstractTransform.
Any time you call transform->TransformPoint() or any similar
method, the Update() method of the transform is automatically called.
It is written out clearly in the header file:
  void TransformPoint(const float in[3], float out[3]) {
    this->Update(); this->InternalTransformPoint(in,out); };

Classes such as vtkImageReslice or vtkTransformPolyDataFilter 
will usually call transform->Update() at the beginning
of every Execute() cycle and then call transform->InternalTransformPoint()
for each transformed point (transform->InternalTransformPoint is identical
to transform->TransformPoint except for the lack of Update).

 - David

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

On 20 Mar 2001, Alexandre Guimond wrote:

> Hi all.  I build a little object that does image registration and
> outputs a vtkAbstractTransform.  It is derived from vtkProcessObject.
> The problem I have is that when I want use the resulting
> transformation, for example with vtkImageReslice, I have to call
> RegistrationObject->Update() explicitly since there is no automatic
> update mechanism for vtkAbstractTransform such as there is for
> vtkDataObject, or at least none that I know of.  Is there a simple way
> of implementing this sort of thing in vtk, or would I have to through
> and develop the same type of update process that exists with
> vtkSource/vtkDataObject?
> thx for the info.

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