[vtkusers] vtkContourFilter rounding issue with vtkIntArray
Bengt Rosenberger
bengt at ctech.com
Thu Jul 23 13:01:25 EDT 2015
Small correction: vtkDataArrayInterpolateTuple is either called from
vtkDataArray, ln 496 or ln 515. I can't exactly tell because I'm unable
to step through that macro. However, I could see that
vtkDataArrayInterpolateTuple, ln 103 was called.
Is there just a vtkDataArrayRoundIfNecessary missing?
Bye,
Bengt
Am 23.07.2015 um 18:50 schrieb Bengt Rosenberger:
> Hi Cory,
>
> thanks for the reply.
>
> When you run the provided code with the provided data, the
> interpolation for the int data ultimately happens in
> vtkDataArray::InterpolateEdge, ln 520, which in turn calls
> vtkDataArrayInterpolateTuple, ln 103. This one performs a
> multiplication with double and then casts back to the type Scalar, it
> does not round the final interpolant. The overload above it does tho,
> but it's not called.
>
> Hope that helps,
> Bengt
>
> Am 23.07.2015 um 15:30 schrieb Cory Quammen:
>> Bengt,
>>
>> From what I can tell looking at the interpolating code in
>> vtkDataArray.cxx, it looks like integer types should be rounded, and
>> it looks like this support has been in VTK for a long time. Can you
>> point out where in VTK you are seeing the casting back to integer
>> type instead of rounding? You may have discovered a bug.
>>
>> Thanks,
>> Cory
>>
>> On Wed, Jul 22, 2015 at 6:05 PM, Bengt Rosenberger <bengt at ctech.com
>> <mailto:bengt at ctech.com>> wrote:
>>
>> Hello everyone!
>>
>> Sorry if this may appear twice on the mailing list, the first
>> time I've submitted this the attachment prevented this to show
>> up. This time I'll provide a link to my DropBox for the data.
>>
>> Anyway, we encountered an issue with vtkContourFilter.
>> Specifically, we have an unstructured grid containing the data to
>> contour with and an additional vtkIntArray. The data in the int
>> array is supposed to be of all the same value, in this case 3.
>> However, after running the field through the contour filter, the
>> int data contains values of 2 as well.
>>
>> After digging deeper into the VTK code, we discovered that the
>> data for the int array is cast to double, interpolated and then
>> cast back to int.
>>
>> So my question is:
>> Why aren't the data values being rounded after interpolation, but
>> instead just cast back to int? Is there a way to enable rounding
>> or copying for only a single array in the grid?
>>
>> Thank you!
>>
>> Here's the data:
>> https://dl.dropboxusercontent.com/u/16837761/test1.7z
>> And here's the code we used for testing:
>>
>> #include <cstdint>
>> #include <vtkSmartPointer.h>
>> #include <vtkUnstructuredGrid.h>
>> #include <vtkCellArray.h>
>> #include <vtkContourFilter.h>
>> #include <vtkPointData.h>
>> #include <vtkXMLUnstructuredGridReader.h>
>>
>> // Checks whether the geo_layer values are all constant
>> void check_geo_layer(vtkDataSet* ds)
>> {
>> if (ds->GetNumberOfCells() == 0)
>> {
>> assert(false);
>> }
>>
>> vtkDataArray* geoLayerData =
>> ds->GetPointData()->GetArray("Geo_Layer");
>>
>> double geoLayer =
>> geoLayerData->GetComponent(ds->GetCell(0)->GetPointId(0), 0);
>> for (uint32_t i = 0; i < ds->GetNumberOfCells(); ++i)
>> {
>> vtkCell* c = ds->GetCell(i);
>> for (uint32_t j = 0; j < c->GetNumberOfPoints(); ++j)
>> {
>> double gl =
>> geoLayerData->GetComponent(c->GetPointId(j), 0);
>> if (gl != geoLayer)
>> {
>> assert(false);
>> }
>> }
>> }
>> }
>>
>> template <class T>
>> void check_geo_layer(vtkSmartPointer<T> vtkFilter)
>> {
>> vtkFilter->Update();
>> auto result = vtkFilter->GetOutput();
>> vtkDataSet* ds = vtkDataSet::SafeDownCast(result);
>>
>> check_geo_layer(ds);
>> }
>>
>> int _tmain(int argc, _TCHAR* argv[])
>> {
>> // Read the test field
>> // Field has one vtkDoubleArray ("TOTHC") and one vtkIntArray
>> ("Geo_Layer")
>> vtkSmartPointer<vtkXMLUnstructuredGridReader> reader =
>> vtkSmartPointer<vtkXMLUnstructuredGridReader>::New();
>> reader->SetFileName("C:\\test1.vtk");
>> reader->Update();
>> vtkDataSet* g1 = reader->GetOutputAsDataSet();
>>
>> // Values in Geo_Layer are supposed to be all 3's. Check that
>> now for the input.
>> check_geo_layer(g1);
>>
>> const double isoValue = 0.98712348937988281;
>>
>> vtkSmartPointer<vtkContourFilter> contour =
>> vtkContourFilter::New();
>> contour->SetInputData(g1);
>> contour->ReleaseDataFlagOn();
>> contour->GenerateTrianglesOn();
>> contour->ComputeGradientsOff();
>> contour->ComputeNormalsOff();
>> contour->ComputeScalarsOff();
>> contour->SetNumberOfContours(1);
>> contour->SetValue(0, isoValue);
>> contour->SetInputArrayToProcess(0, 0, 0,
>> vtkDataObject::FIELD_ASSOCIATION_POINTS, "TOTHC");
>>
>> // Check again whether values in Geo_Layer are only 3's.
>> // PROBLEM: They are not. There are 2's in there as well,
>> which occur from interpolating integers and not rounding in the end.
>> // You can see the problem if you convert
>> Geo_Layer to a vtkDoubleArray, in which case values of
>> 2.9999999998 may appear after contouring.
>> check_geo_layer(contour);
>>
>> std::cin.ignore();
>> }
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>>
>>
>> --
>> Cory Quammen
>> R&D Engineer
>> Kitware, Inc.
>
>
>
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