[vtk-developers] vtkProcrustesAlignmentFilter

[David Gobbi]

Hi Tim,

A general rigid-body alignment class would be a good thing.
It would be difficult to base it on transforms, because there
is one transform per data set.

Also there is the issue that generating a transform as part
of a VTK pipeline can be a pain.  This could be fixed if
vtkAbstractTransform became a subclass of vtkDataObject so that
a transform can have a 'source'.  In this scenario, you could
build your class as you have described it but there would
be a 'GetTransformCollection' method to get all the transforms.

Because the 'vtkDataSetCollectionSource' doesn't yet exist,
you might want to just use the usual 'SetInput(i,inputI)'
and 'GetOutput(i)' methods (and perhaps later add a
GetTransform(i) method).  The inheritance tree would then
be

vtkSource
 |
vtkProcrustesAlignmentFilter

and could later be expanded to

vtkSource
 |
vtkMultiplePointSetToMultiplePointSetFilter
 |
vtkProcrustesAlignmentFilter

This matches a little better with the existing VTK filters.
Also, note that a 'Collection' is not a vtkDataObject so having a
method with the signature

 vtkDataSetCollection *GetOutput();

just isn't right IMHO while

 vtkPointSet *GetOutput(int i);

looks quite friendly.

 - David


On Mon, 7 Jan 2002, Tim Hutton wrote:

> Hello developers,
>
> There are a couple of us that are keen to provide an implementation of the
> Procrustes algorithm for aligning a set of objects together in a least
> squares sense. Its functionality is somewhat similar to
> vtkLandmarkTransform except that it would take a collection of datasets
> instead of two. This would be useful for building models from collections
> of objects and is a core part of many other algorithms.
>
> I (we) have two questions:
>
> 1) Would VTK benefit by having such a class? Perhaps Procrustes is not a
> pure visualization technique but then neither is
> vtkThinPlateSplineTransform which is used by lots of people.
>
> 2) How would such a class be best implemented? I have envisaged an
> inheritance tree like this:
>
> vtkSource
> |
> vtkDataSetCollectionSource
> |
> vtkDataSetCollectionToDataSetCollectionFilter
> |
> vtkProcrustesAlignmentFilter
>
> Is this sensible? Maybe it should be based on transforms instead?
>
> Any comments welcome. Thankyou!
>
> Tim.
> ---------------------------------------------------------------------------
> Tim Hutton,                        http://www.eastman.ucl.ac.uk/~dmi/MINORI
> Research Fellow & PhD student,                   T.Hutton at eastman.ucl.ac.uk
> MINORI Project, Biomedical Informatics Unit,     Tel: [+44] (0)20 7915 2344
> Eastman Dental Institute, UCL,                   Fax: [+44] (0)20 7915 2303
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