[vtkusers] PCA on vtkImageData

[David Gobbi]

Hi Andrew,

It should export all the points in the volume, as long as they are within
the applied thresholds.  What is your evidence that it's only exporting the
boundary?

 - David

On Mon, Nov 17, 2014 at 9:34 AM, Andrew Crozier <
andrew.crozier at medunigraz.at> wrote:

>  Hi David,
>
> Thanks for the suggestion. I looked at the vtkThreshold filer, however it
> appears to export the boundary of the thresholded volume, whereas I require
> all points inside the volume. Have you any idea of how to achieve that?
>
> BW,
> Andrew
>
>
> On 17/11/14 17:16, David Gobbi wrote:
>
> Hi Andrew,
>
>  The vtkThreshold filter will extract only the cells with the desired
> scalar values, and will output them as an unstructured grid.  It
> isn't exactly what you want because it extracts cells, rather than
> points, but it might be worth a shot.
>
>   - David
>
> On Mon, Nov 17, 2014 at 8:28 AM, Andrew Crozier <
> andrew.crozier at medunigraz.at> wrote:
>
>> Hi,
>>
>> I am trying to evaluate the principal components of a strucutre in a 3D
>> volume image, to determine its spatial alignment for use in an automatic
>> processing pipeline.
>>
>> The input is a vtkImageData, with multiple integer values (say, 0, 1, 2
>> and 3), and I want to perform PCA on the positions of all voxels with value
>> 2, for example.
>>
>> I have looked at vtkPCAAnalysisFilter, and this requires an input of
>> vtkPointSet. vtkImageDataToPointSet converts a vtkImageData to a
>> vtkStructuredGrid, however I expect this to include all points in the
>> original image. At the moment I seem to be missing some way of filtering
>> out the points other than those of value 2.
>>
>> Any help provided for this would be greatly appreciated!
>>
>> Best wishes,
>> Andrew Crozier
>>
>>
> --
> ------------------------------
> *Andrew Crozier*
> andrew.crozier at medunigraz.at
>
> Postdoctoral Researcher
> Institute for Biophysics
> Medical University of Graz
>
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