[vtkusers] how to cast a vtkDataArray from one type into another?

[Jérôme]

Hi,

SafeDownCast is a simple call of static_cast adding an inheritance check.
If you call A->SafeDownCast( B), it will check that B is a A (and perform
the cast if yes). In your case, vtkDoubleArray is *not* a vtkIntArray.
That's why you cannot cast in that way.

You should take a look at vtkImageCast filter, that is able to cast scalars
between different types.

Hope that helps,
Jerome

2009/10/8 David Doria <daviddoria+vtk at gmail.com <daviddoria%2Bvtk at gmail.com>
>

>
> On Tue, Oct 6, 2009 at 4:30 PM, Fabio Meneghini <fab.meneghini at gmail.com>wrote:
>
>> Hi all,
>> just like the subject of this topic says:
>> Let's suppose I got a vtkPolyData with one vtkDataArray field with scalar
>> values, of type unsigned char.
>> Is there a way to quickly cast all the unsigned char values after loading
>> and before visualizing the data??
>>
>> Thanks in advance,
>>
>> Cheers.
>>
>> Fabio Meneghini
>>
>
> I thought SafeDowncast would do this - but I guess not? Can anyone explain
> why this example does not work (my "invalid cast" output is hit):
>
> #include <vtkDoubleArray.h>
> #include <vtkIntArray.h>
> #include <vtkPoints.h>
> #include <vtkPolyData.h>
> #include <vtkPointData.h>
>
> #include <iostream>
>
> int main(int argc, char *argv[])
> {
>     //create points
>     vtkPoints* Points = vtkPoints::New();
>
>     unsigned int NumberOfPoints = 3;
>     Points->InsertNextPoint(0.0, 0.0, 0.0);
>     Points->InsertNextPoint(1.0, 0.0, 0.0);
>     Points->InsertNextPoint(0.0, 1.0, 0.0);
>
>     //add the points to a polydata
>     vtkPolyData* polydata = vtkPolyData::New();
>     polydata->SetPoints(Points);
>
>     //add distances to each point
>     vtkDoubleArray* Distances = vtkDoubleArray::New();
>     Distances->SetNumberOfComponents(1);
>     Distances->SetName("Distances");
>
>     Distances->InsertNextValue(1.1);
>     Distances->InsertNextValue(2.2);
>     Distances->InsertNextValue(3.3);
>
>     polydata->GetPointData()->AddArray(Distances);
>
>     //get the distances from the polydata
>     vtkDoubleArray* Array =
> vtkDoubleArray::SafeDownCast(polydata->GetPointData()->GetArray("Distances"));
>
>     if(Array)
>     {
>         for(unsigned int i = 0; i < NumberOfPoints; i++)
>         {
>             double dist;
>             dist = Array->GetValue(i);
>             std::cout << "Distance: " << dist << std::endl;
>         }
>     }
>
>     //cast the double distances to ints
>     vtkDoubleArray* DoubleDistances =
> vtkDoubleArray::SafeDownCast(polydata->GetPointData()->GetArray("Distances"));
>     vtkIntArray* IntDistances = vtkIntArray::SafeDownCast(DoubleDistances);
>
>     if(IntDistances)
>     {
>         for(unsigned int i = 0; i < NumberOfPoints; i++)
>         {
>             int dist;
>             dist = IntDistances->GetValue(i);
>             std::cout << "Distance: " << dist << std::endl;
>         }
>     }
>     else
>     {
>         std::cout << "invalid cast." << std::endl;
>     }
>
>     return 0;
> }
>
>
> Thanks,
>
> David
>
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