[vtkusers] problem with vtkvolume16reader->GetOutput()->GetScalarPointer()??

[Amy Henderson]

No, an explicit call to Update() does not need to be made in these examples 
because the data is not being modified outside the visualization pipeline, 
and the whole pipeline is updated when the first Render() happens. In this 
case, a Render() call happens when Initialize() is called on the 
vtkRenderWindowInteractor.

- Amy

At 04:58 AM 5/4/2004, Veerapuram Varadhan wrote:
>Hi Amy,
>
>Probably we might have to reflect the said change in
>VTK/Examples/Medical/Cxx/Medical1.cxx
>VTK/Examples/Medical/Cxx/Medical2.cxx and
>VTK/Examples/Medical/Cxx/Medical3.cxx
>as well.
>
>V. Varadhan.
>
> > Hi Nicolas,
> >
> > This problem is very similar to your previous problem. In this case, the
> > scalars haven't been filled in yet because the data has not been read from
> > the file. Add v16->Update(); before you try to access this reader's
> > output.
> > This is true for all readers, filters, etc. in VTK. Their output is not
> > valid until Update has been called on them. The VTK rendering process
> > updates your visualization pipeline for you, which is why you don't have
> > to
> > call Update yourself if you are rendering the results without modifying
> > them first.
> >
> > - Amy
> >
> > At 06:06 AM 5/1/2004, Dumont Nicolas wrote:
> >>Hello users!!
> >>
> >>I wish to make a copy of my volume data in a new vtkimagedata object, so
> >>after that i could modify the scalar data at the voxels (for example to
> >>make a spherical hole inside the volume).
> >>
> >>The code I wrote works well with
> >>
> >>vtkPNGreader->GetOutput()->GetScalarPointer();
> >>
> >>but the same code adapted for
> >>
> >>vtkVolume16reader->GetOutput()->GetScalarPointer();
> >>
> >>returns me the error that GetScalarPointer() points to memory
> >> 0x0000000000
> >>and so cant be read.
> >>
> >>Any body has an idea why it is so ?
> >>
> >>Nicolas D.
> >>Ulg, Belgium
> >>
> >>
> >>
> >>Here are both pieces of code:
> >>
> >>****************************************************
> >>vtkPNGReader * reader = vtkPNGReader::New();
> >>         reader->SetFilePattern("MR/%d.png");
> >>         reader->SetDataExtent(1,256,1,256,0,126);
> >>         reader->SetDataSpacing(1,1,1.5);
> >>         reader->SetDataOrigin(0,0,0);
> >>         reader->UpdateWholeExtent();
> >>
> >>
> >>vtkImageData *imageData = vtkImageData::New();
> >>         imageData->SetDimensions(256,256,126);
> >>         imageData->SetSpacing(1,1,1.5);
> >>         imageData->SetOrigin(0.0,0.0,0.0);
> >>         imageData->SetScalarTypeToUnsignedChar();
> >>         imageData->SetNumberOfScalarComponents(1);
> >>         imageData->AllocateScalars();
> >>         imageData->GetPointData()->CopyScalarsOn();
> >>
> >>unsigned char *ptrReader =
> >>(unsigned char *) reader->GetOutput()->GetScalarPointer();
> >>unsigned char *ptrData =
> >>(unsigned char *) imageData->GetScalarPointer();
> >>
> >>for (int i=0; i<256*256*126; i++)
> >>{
> >>         *ptrData = *ptrReader;
> >>         ptrData++;
> >>         ptrReader++;
> >>}
> >>
> >>//...
> >>     volumeMapper->SetInput(imageData);
> >>//...
> >>
> >>***********************************************************************
> >>vtkVolume16Reader *v16 = vtkVolume16Reader::New();
> >>     v16->SetDataDimensions(64,64);
> >>     v16->SetDataByteOrderToLittleEndian();
> >>     v16->SetFilePrefix ("quarter");
> >>     v16->SetImageRange(1, 93);
> >>     v16->SetDataSpacing (3.2, 3.2, 1.5);
> >>
> >>vtkImageData *imageData = vtkImageData::New();
> >>         imageData->SetDimensions(64,64,93);
> >>         imageData->SetSpacing(3.2,3.2,1.5);
> >>         imageData->SetOrigin(0.0,0.0,0.0);
> >>         imageData->SetScalarTypeToUnsignedChar();
> >>         imageData->SetNumberOfScalarComponents(1);
> >>         imageData->AllocateScalars();
> >>         imageData->GetPointData()->CopyScalarsOn();
> >>
> >>unsigned char *ptr2 =
> >>(unsigned char *) v16->GetOutput()->GetScalarPointer();
> >>unsigned char *ptr =
> >>(unsigned char *) imageData->GetScalarPointer();
> >>
> >>for (int i=0; i<64*64*93; i++)
> >>{
> >>         *ptr = *ptr2;
> >>         ptr++;
> >>         ptr2++;
> >>}
> >>//...
> >>     volumeMapper->SetInput(imageData);
> >>//...
> >>
> >>
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> >
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