Dodgy UpdateExtent

[John Biddiscombe]

Dear vtk...

If you do 
1) Create a StructuredPoints dataset
2) Set dimensions/spacing and origin
3) Set correct scalars in sp data
4) Create a DatasetWriter
5) writer->SetInput(structuredpoints)
6) writer->Write

you get a dataset (file) with dimensions 1,1,1 nomatter what you do <gulp>.

It seems that DataSetWriter calls MakeImageToStructurdPoints and it in turn
checks UpdateExtent (on itself effectively) in its Execute method, which by
default is {0,0,0,0,0,0)

consequently nothing gets copied from the structured points dataset to the
(new copy of the) structuredpoints dataset and the writer doesn't bother
writing anything impressive.

here's some code

    vtkStructuredPoints *coverage = vtkStructuredPoints::New();
    int newdims[3] = {1400,2000,1};
    float origin[3] = {0,0,0};
    float spacing[3] = {500,500,1};
    coverage->SetDimensions(newdims);
    coverage->SetOrigin(origin);
    coverage->SetSpacing(spacing);
    //
    vtkScalars *coveragescalars = vtkScalars::New(VTK_FLOAT,2);
    coveragescalars->SetNumberOfScalars(newdims[0]*newdims[1]);
    //
    // large loop filling scalars with data goes here
    //
    coverage->GetPointData()->SetScalars(coveragescalars);
    coveragescalars->SetActiveComponent(0);
    //
    vtkDataSetWriter *wri = vtkDataSetWriter::New();
    wri->SetFileName("E:\\Final_plot.vtk");
    wri->SetInput(coverage);
    wri->Update(); // or Write();

To my mind the code above seems OK, but clearly I need to insert an extra
SetUpdateExtent somewhere. For now I'll do this, but is this a flaw or have
I (yet again!) missed something. <sigh>

John B



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