Fwd: Re: Fwd: Re: User Transform....

[Lisa Sobierajski Avila]

>Date: Thu, 23 Mar 2000 14:52:01 -0500
>To: David Gobbi <dgobbi at irus.rri.on.ca>
>From: Lisa Sobierajski Avila <lisa.avila at kitware.com>
>Subject: Re: Fwd: Re: User Transform....
>Cc: vtkdevelop at public.kitware.com
>
>Hello David,
>
>I see what you are trying to do, and I was faced with the same problem at 
>one point with vtkPiecewiseFunction - I needed it to be an output of 
>something and work in a pipeline. The solution I took in that case was to 
>make vtkPiecewiseFunction a subclass of vtkDataObject. That was an ok 
>solution there, but wouldn't work (with vtk "as is") for you since 
>vtkDataObject is pretty heavy weight.
>
>Here is a suggestion I have (and I throw this out to everyone on 
>vtkdevelop for comment). I would like to make vtkDataObject as light 
>weight as possible - remove most of the ivars. Then create a new subclass 
>with those ivars back in it, and vtkDataSet would be a subclass of this 
>new class. vtkMatrix4x4, vtkPiecewiseFunction, and whatever else needs to 
>be would be subclasses of vtkDataObject.  This way you could do 
>actor->SetUserMatrix(yourfilter->GetOutput()) where the GetOutput() method 
>of your filter would return a vtkMatrix *. vtkMatrix would be modified to 
>call Update() on its source when necessary (or do nothing if its source is 
>NULL) With these changes you could remove the SetUserTransform from vtkProp3D.
>
>I'll probably go ahead and try this out in the next few days to see how it 
>works out. It will take a bit of thought to determine how much 
>functionality to provide - the basic data object won't support streaming 
>so it won't need to store any extent / pieces information and it won't 
>support data releasing, but can a vtkMatrix4x4 move across a input/output 
>port? Not that the ports are back in yet - but they will be soon....
>
>
>Lisa
>
>
>
>
>At 03:17 PM 3/22/00, you wrote:
>>The answer to the UserTransform ivar in vtkProp3D. I'm studying this to 
>>see what impact it has on the picking.
>>Will
>>
>> >Date: Wed, 22 Mar 2000 14:55:50 -0500 (EST)
>> >From: David Gobbi <dgobbi at irus.rri.on.ca>
>> >X-Sender: dgobbi at localhost.localdomain
>> >To: Will Schroeder <will.schroeder at kitware.com>
>> >Subject: Re: User Transform....
>> >
>> >Hi Will,
>> >
>> >The UserTransform serves the same purpose as the UserMatrix.
>> >That much is obvious, so here is why just doing
>> >actor->SetUserMatrix(transform->GetMatrixPointer())
>> >is different from doing
>> >actor->SetUserTransform(transform):
>> >
>> >The new set of transforms that I've implemented are pipelined.
>> >When you call  transform->TransformPoint(inPoint,outPoint)
>> >or  transform->TransformPoints(inPoints,outPoints)
>> >the class first calls its 'Update()' method before proceeding.
>> >
>> >The vtkTransform::Update() method is empty, but e.g.
>> >vtkLandmarkTransform::Update() uses this->SourceLandmarks
>> >and this->TargetLandmarks to make a 4x4 registration matrix.
>> >The vtkLinearTransformConcatenation::Update() method looks at
>> >its list of transforms and concatenates all their matrices.
>> >
>> >
>> >So, the reason that actor->SetUserMatrix(transform->GetMatrixPointer())
>> >is insufficient is that it 'breaks the pipeline', i.e. the matrix
>> >will only be updated if the user explicitly calls Update() on the
>> >transform.
>> >
>> >
>> >For example, in my lab we have a vtkFlockTracker class that interfaces
>> >to the Flock of birds.  We want to get a transform from the flock,
>> >apply various calibrations, and then pass the result on to an actor.
>> >
>> >                             flockTracker
>> >                                  |
>> >                                  v
>> >         calibrationTrans1    flockTrans    calibrationTrans2
>> >                    |             |              |
>> >                    |             v              |
>> >                    \-->  concatenationTrans  <--/
>> >                                  |
>> >                                  v
>> >                           flockActor->SetUserTransform()
>> >
>> >I'm not sure how clear the diagram is, but the idea is that when
>> >flockActor needs do 'do its stuff,' it calls calibrationTrans->GetMatrix()
>> >which (internally) calls calibrationTrans->Update() which causes
>> >calibrationTrans1, flockTrans, and calibrationTrans2 to be concatenated.
>> >
>> >
>> >So, to make a long story short, back a couple years ago when I started
>> >using VTK the data pipeline made a lot of sense... but I really wished
>> >that I could pipeline operations on transforms as well.  It wasn't
>> >until a few months ago that I started actually writing the code.
>> >
>> >  - David
>> >
>> >
>> >P.S.  In general I've been working on this more-or-less independently
>> >       and with little feedback, perhaps most VTK users simply don't
>> >       work with transforms much or take viewpoint that 'it's nice, but
>> >       can't you do that already with assemblies?'  Not that lack
>> >       of feedback would ever keep me from monkeying around with VTK
>> >       as long as I have CVS access...
>> >
>> >--
>> >   David Gobbi, MSc                    dgobbi at irus.rri.on.ca
>> >   Advanced Imaging Research Group
>> >   Robarts Research Institute, University of Western Ontario
>> >
>> >On Wed, 22 Mar 2000, Will Schroeder wrote:
>> >
>> > >
>> > > Hi David-
>> > >
>> > > Can you help me here? The UserTransform, how do you use and what's 
>> it for?
>> > >
>> > > Will
>> > >