[vtkusers] Histogram of a data array?

[John Biddiscombe]

> I would like to calculate a histogram of some scalar data that is
> associated with a vtkUnstructuredGrid dataset.  How do I convert my
> vtkDataArray into vtkImageData (single component) so that I can use
> vtkImageAccumulate to calculate the histogram?  I think it should be
> something like this, but not sure how to convert the data array:

Assuming you are only interested in the histogram and know that the
topological information is lost,

>   vtkDataArray *data = ug->GetPointData()->GetScalars();
>
>   // ?? vtkDataArrayToImageDataFilter ??
>   vtkDataArrayToImageDataFilter *imageData;
>     imageData->SetInput(data);

try this...

vtkImageData *dummyHolder = vtkImageData::New();
  int N = data->GetNumberOfTuples();
\\ create a one dimensional image with N tuples
  dummyHolder->SetDimensions(N,1,1);
  dummyHolder->GetPointData()->SetScalars(data);


>   vtkImageAccumulate *histogram;

     histogram->SetInput(dummyHolder);

You may need to fiddle with a few other parameters, but the above ought to
do the right thing

JB