vtkImageData: SetScalarComponentFromDouble do not change GetScalarRange

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1

For a vtkImageData, I want to modify the scalar using SetScalarComponentFromDouble. But, I find the GetScalarRange do not return the correct result after SetScalarComponentFromDouble.

My test code is:

import vtkmodules.all as vtk

img = vtk.vtkImageData()
img.SetDimensions(100, 100, 1)
img.AllocateScalars(vtk.VTK_DOUBLE, 1)

for i in range(100):
    for j in range(100):
        img.SetScalarComponentFromDouble(i, j, 0, 0, i+j)

range1 = img.GetScalarRange()
print('range1: ', range1)

img.SetScalarComponentFromDouble(0, 0, 0, 0, 1000)
img.Modified()
range2 = img.GetScalarRange()
print('range2: ', range2)

The range2 is the same with range1 (0~198) even img.SetScalarComponentFromDouble(0, 0, 0, 0, 1000).

After look at the c++ code, I find that the range do not computer after SetScalarComponentFromDouble. For vtkDataArray, the GetRange explain that:

The range is computed and then cached, and will not be re-computed on subsequent calls to GetRange().

How can I force it to re-compute range?

2

The explanation of vtkDataArray::ComputeRange said: “Call ClearRange to force a recomputation if it is needed.”

  1. I can not find ClearRange method in vtk.
  2. How to call ClearRange in vtkImageData?
3

The ClearRange() method doesn’t exist in VTK anymore (I’m not sure when it was removed).

But to answer your original question, instead of img.Modified(), call the following:

img.GetPointData().GetScalars().Modified()

To see why, consider how SetScalarComponentFromDouble() is implemented in vtkImageData.cxx:

vtkIdType index = this->GetScalarIndex(x, y, z);
vtkDataArray* scalars = this->GetPointData()->GetScalars();
scalars->SetComponent(index, comp);

The Set method is being called on the vtkDataArray object.

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