[vtkusers] How can I use vtkPolyData as a Implicit function of vtkClipPolyData?

[Seungbum Koo]

Dear vtk Users,

I'm using vtk3.2 and I have read manuals and vtkusers Archives over and 
over but
I couldn't figure out how to convert my vtkPolyData into 
vtkImplicitFunction to use
it in vtkClipPolyData.
What I want to do is clipping between a vtkPolyData and a vtkPolyData.
Some people made classes likes vtkImplicitPolyData but I want to do this 
using only
vtk if possible, so I tried some test cases.

First, I made one vtkSphereSource as a vtkPolyData source, and one 
vtkSphere as a vtkImplicitFunction
for vtkClipPolyData. It worked fine.
Second, I made one vtkSphereSource as a vtkPolyData source, and another 
vtkSphereSource and
filtered is using vtkImplicitDataSet to use it as a vtkImplicitFunction. It 
didnt' work and I received a
messages "can't evaluate function".
I looked into the function EvaluateFunction in vtkImplicitDataSet and it 
couldn't evaluate
vtkSphereSource beacuse it didn't have scalar value. (I'm very confused 
what the scalar
value should be in sphere.), So, I made some scalar values for the 
vtkSphereSource.
But next, FindAndGetCell() in EvaluateFunction couldn't find any cell 
around a point.

Does anyone know how to do vtkClipPolyData between two vtkPolyData's like 
this case?

Seungbum
koosb at stanford.edu
----------------------------------------------------------------
Source for First case:
	vtkSphereSource *pSphere1 = vtkSphereSource::New();
	pSphere1->SetRadius(50);
	pSphere1->SetCenter(0,0,0);
	vtkSphere *pSphere2 = vtkSphere::New();
	pSphere2->SetRadius(50);
	pSphere2->SetCenter(0,0,50);
	vtkClipPolyData *pClip = vtkClipPolyData::New();
	pClip->SetInput(pSphere1->GetOutput());
	pClip->SetClipFunction(pSphere2);
	pClip->GenerateClipScalarsOn();
	pClip->GenerateClippedOutputOn();

Source for Second case:
	vtkSphereSource *pSphere1 = vtkSphereSource::New();
	pSphere1->SetRadius(50);
	pSphere1->SetCenter(0,0,0);
	vtkSphereSource *pSphere2 = vtkSphereSource::New();
	pSphere2->SetRadius(50);
	pSphere2->SetCenter(0,0,50);
	vtkImplicitDataSet *pIdata = vtkImplicitDataSet::New();
	pIdata->SetDataSet(pSphere2->GetOutput());
	vtkClipPolyData *pClip = vtkClipPolyData::New();
	pClip->SetInput(pSphere1->GetOutput());
	pClip->SetClipFunction(pIdata);
	pClip->GenerateClipScalarsOn();
	pClip->GenerateClippedOutputOn();

	vtkScalars pScalars = vtkScalars::New();
	for(int i=0; i<pSphere2->GetOutput()->GetNumberOfPoints(); i++)
		pScalars->InsertNextScalar(1.0);
	pSphere2->GetOutput()->GetPointData()->SetScalars(pScalars);