[vtk-developers] Problem with using vtkArrayCalculator to extract fields for vtkImageFFT Processing

[Randall Hand]

Well, I'm building a vtkDoubleArray, and the vtkArrayCalculator claims it's 
returning a vtkDoubleArray.. So that shouldn't be the case in this 
situation.

On 9/14/05, Berk Geveci <berk.geveci at gmail.com> wrote:
> 
> This is a guess but if the array calculator outputs a data type than
> the input's scalars, no imaging filter can be used down the pipeline.
> This is a known bug. Essentially no (non-imaging) filter that changes
> the data type of the scalars is allowed in a pipeline with imaging
> filters. There is work (slow) going on to fix this issue. I would not
> hold my breath for it's completion.
> 
> On 9/14/05, Randall Hand <randall.hand at gmail.com> wrote:
> > Ok, I posted this once before, but here it is again with some more
> > information.
> >
> > I've written a piece of code to create a synthetic dataset. It's a 128^3
> > dataset, each point with a 3-component double value consisting of 
> (sin(x),
> > junk, morejunk). I extract just the first component, and do an FFT. 
> You'll
> > find the code at the end of this message, along with my 
> "PrintStatistics"
> > function attached.
> >
> > You'll see from the #if/#endif blocks that there's two possible ways to 
> do
> > it. The first is with a vtkArrayCalculator, where I set a very trivial
> > function to simply copy out the one value. The other way is with a
> > vtkImageExtractComponents. When doing it with the vtkArrayCalculator, 
> the
> > filter seems to work just fine but then the FFT yields values like :
> >
> > p Array [0]: vtkDoubleArray "result", 2,097,152 points, 8 bytes per
> > point
> > p Magnitude Range: 0.0000 1482912.5793
> > p Component 0 Range: -1048575.9848
> > 1048575.8760
> > p Component 1 Range: -1048572.9243
> > 1048579.0968
> > With a simple sin wave, the result should be almost purely imaginary, so
> > the Component 0 range should be almost 0 to 0.
> >
> > When I switch to using the vtkImageExtractComponents, the results look
> > better:
> >
> >
> > p Array [0]: vtkDoubleArray "image", 2,097,152 points, 8 bytes per
> > point
> > p Magnitude Range: 0.0000 1048576.0091
> > p Component 0 Range: -0.0557 0.0011
> > p Component 1 Range: -1048576.0089
> > 1048576.0091
> >
> >
> > Unfortunately, when working with the vtkImageExtractComponents filter, I
> > lose the other two fields if I had planned on using them for coloring or
> > something. Also, my results aren't quite what I expected. Much better, 
> but
> > on more complex datasets I seem to get results that are a little off 
> from
> > the expected result. I don't know if the cause of all this is related, 
> but
> > I'm chasing down what I can.
> >
> > So, any ideas?
> >
> > ----- Code starts here -------
> >
> > #include <stdio.h>
> > #include <string.h>
> > #include <stdlib.h>
> > #include <unistd.h>
> > #include "stat.h"
> > #include <sys/types.h>
> > #include <sys/stat.h>
> > #include <sys/mman.h>
> > #include <fcntl.h>
> > #include <vtkObject.h>
> > #include "vtkImageData.h"
> > #include "vtkPointData.h"
> > #include <vtkDataArray.h>
> > #include <vtkUnsignedCharArray.h>
> > #include <vtkDoubleArray.h>
> > #include <vtkImageData.h>
> > #include <vtkImageFFT.h>
> > #include <vtkArrayCalculator.h>
> > #include <vtkImageExtractComponents.h>
> >
> > int main (int argc, char *argv[])
> > {
> > double *data;
> > int xdim, ydim, zdim;
> > double kx;
> > int x,y,z;
> > long index;
> > xdim = 128;
> > ydim = 128;
> > zdim = 128;
> >
> > if ((data =
> > (double*)malloc(sizeof(double)*xdim*ydim*zdim*3)) == NULL)
> > {
> > perror("Unable to allocate memory!\n\t");
> > return -1;
> > }
> >
> > printf("Constructing sin(kx * x) dataset...\n");
> > kx = 2.0 * 3.1415926 / (double)xdim;
> > for(x=0; x<xdim; x++) {
> > for(y=0; y<ydim; y++) {
> > for(z=0; z<zdim; z++) {
> > index = z + (y*zdim) + (x * ydim * zdim);
> > data[(index*3)+0] = sin(kx * (double)x);
> > data[(index*3)+1] = cos(kx * (double)x);
> > data[(index*3)+2] = tan(kx * (double)x);
> > }
> > }
> > }
> >
> > vtkDoubleArray *ucPointer = vtkDoubleArray::New();
> > ucPointer->SetNumberOfComponents(3);
> > ucPointer->SetArray(data, xdim*ydim*zdim*3, 1);
> > ucPointer->SetName("image");
> >
> > vtkImageData *image = vtkImageData::New();
> > image->Initialize();
> > image->SetDimensions(xdim, ydim, zdim);
> > image->SetExtent(1, xdim, 1, ydim, 1, zdim);
> > image->SetScalarTypeToDouble();
> > image->SetNumberOfScalarComponents(3);
> > image->GetPointData()->SetScalars(ucPointer);
> > PrintStatistics(image);
> > printf("Extracting Velocity X-Component...\n");
> >
> > #if 0
> > vtkArrayCalculator *extract = vtkArrayCalculator::New();
> > extract->SetInput(image);
> > extract->SetResultArrayName("result");
> > extract->AddScalarVariable("x", "image", 0);
> > extract->SetFunction("(x*1.0)+0.0");
> > extract->ReplaceInvalidValuesOff();
> > extract->Update();
> >
> > extract->GetOutput()->GetPointData()->RemoveArray("image");
> >
> > extract->GetOutput()->GetPointData()->SetActiveScalars("result");
> > #else
> > vtkImageExtractComponents *extract =
> > vtkImageExtractComponents::New();
> > extract->SetInput(image);
> > extract->SetComponents(0);
> > extract->Update();
> > #endif
> > PrintStatistics(extract->GetOutput());
> >
> > printf("Computing FFT...\n");
> > vtkImageFFT *fft = vtkImageFFT::New();
> > fft->SetInput(extract->GetOutput());
> > fft->Update();
> > PrintStatistics(fft->GetOutput());
> >
> > }
> >
> >
> > --
> > Randall Hand
> > Visualization Scientist,
> > ERDC-MSRC Vicksburg, MS
> > Homepage: http://www.yeraze.com
> > _______________________________________________
> > vtk-developers mailing list
> > vtk-developers at vtk.org
> > http://www.vtk.org/mailman/listinfo/vtk-developers
> >
> >
> >
> >
> 



-- 
Randall Hand
Visualization Scientist, 
ERDC-MSRC Vicksburg, MS
Homepage: http://www.yeraze.com
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