[vtk-developers] vtkAssignAttribute and vtkImageData

[Jeff Lee]

Won't vtkExtractVectorComponents work for you?
-Jeff

Miller, James V (Research) wrote:

> There seems to be a problem with vtkAssignAttribute operating on 
> ImageData.
>  
> We were using vtkAssignAttribute to take the vectors of a dataset and 
> use them as multi-component scalars.
> When the dataset is an ImageData, the output of the vtkAssignAttribute 
> filter does not adjust the
> NumberOfScalarComponents of the ImageData.
>  
> These problem arises because ImageData caches the 
> NumberOfScalarComponents from the scalars
> array.  When the number of components in the scalars are changed, the 
> ImageData needs to be told.
> vtkAssignAttributes works generically on DataSets so it doesn't know 
> its operating on an ImageData
> and thus doesn't tell the ImageData that new number of scalar components.
>  
> If a filter after the vtkAssignAttribute in the pipeline querys the 
> ImageData::GetNumberOfScalarComponents()
> instead of ImageData::GetScalars()->GetNumberOfScalarsComponents() 
> then it will not operate properly.
>  
> Possible solutions:
>
>    1. vtkAssignAttributes could check whether it is operating on
>       ImageData and whether the scalars are being modified and the
>       adjust the NumberOfScalarComponents on the ImageData
>       appropriately. This is not too bad an option if ImageData is the
>       only dataset type that caches this information.
>    2. Change
>       ImageData::GetNumberOfScalarComponents()/SetNumberOfScalarComponents()
>       to delegate these calls to the scalars DataArray instead of
>       caching the values.  This could impact how people are
>       constructing ImageData (where they would set the
>       NumberOfScalarComponents on an ImageData, then have the allocate
>       procedures create a scalars DataArray with the proper number of
>       components.
>    3. Deprecate
>       ImageData::GetNumerOfScalarComponents()/GetNumberOfScalarComponents()
>
>  
>  
>
> *Jim Miller*
> */_____________________________________/*
> /Visualization & Computer Vision//
> /GE Research/
> /Bldg. KW, Room C218B/
> /P.O. Box 8, Schenectady NY 12301/
>
> //_millerjv at research.ge.com <mailto:millerjv at research.ge.com>_/
>
> /_james.miller at research.ge.com_/
> /(518) 387-4005, Dial Comm: 8*833-4005, /
> /Cell: (518) 505-7065, Fax: (518) 387-6981/
>
>  
>
>