Help Needed: [vtkusers] Extracting points from within an Implicit Function.

[Rahul Goela]

Hello Vtk Users:

I am currently imvolved in developing a visualization
tool for analysis of 3d data (point form). 

I was facing a very unique problem, for which I have
not been able to find the solution. It is regarding
the vtkImplicitFunctions. 

Problem:

Say there are two spheres and I Union them using
vtkImplicitFunction, I will get a shape of 'dumbell'. 
Now say I have a point cloud, drawn from 30 random 3D
points. This 'dumbell' shape say encloses 5 of these
points in the 3d Space. Is there any way, using VTK
that I get these 5 points ? 

I have tried using a method using 'vtkClipDataSet',
but it doesn't give the result. My source code has
been provided below.

I would be extremely grateful if I could any help
regarding this issue.

Thanks alot,

Best regards,

Rahul
--------------------SOURCE CODE-----------------------

PLOTTING OF POINTS-:

- Three arrays xcon,ycon and zcon have the x,y,z
co-ordinates of these points. 

  //Data to be visualized
  vtkPoints *newPts = vtkPoints::New();
  numPts=30;
  for(i=0; i<numPts; i++)
  {
    xyz[0] = xcon[i]; // put the x,y,z coords into a
                         temp point holder
    xyz[1] = ycon[i]; 
    xyz[2] = zcon[i]; 
    newPts->InsertPoint(i, xyz); 
  }
  aVertex = vtkVertex::New();
  for( int m = 0; m < NumPoints; m++ )
  {
    aVertex->GetPointIds()->InsertNextId(m);
  }
  dataSet = vtkUnstructuredGrid::New();
 
dataSet->InsertNextCell(aVertex->GetCellType(),aVertex->GetPointIds());
  dataSet->SetPoints(newPts);
  
  dataSetMapper = vtkDataSetMapper::New();
  dataSetMapper->SetInput(dataSet);
  
  dataSetActor = vtkActor::New();
  dataSetActor->SetMapper(dataSetMapper);
  dataSetActor->GetProperty()->SetColor(0,0,0);

METHOD FOR EXTRACTING POINTS:
 
vtkPointDataToCellData
*p2c=vtkPointDataToCellData::New();

p2c->SetInput(dataSet);//dataset is the set of points
which are being visualized on the screen

p2c->PassPointDataOn();
 
vtkClipDataSet *clipedData = vtkClipDataSet::New(); 
clipedData->SetClipFunction(ib1); //ib1 is the
implicit function from which the pts have to be
extracted.

//Now add the following code to the clipdataset
clipedData->SetInput(p2c->GetUnstructuredGridOutput());

//clipDataSet->GenerateClippedOutputOn();//This is if
u require the points outside the implict boolean
function

vtkDataSetMapper *dsmapper = vtkDataSetMapper::New(); 
dsmapper->SetInput(clipedData->GetOutput()); 

vtkActor *dsActor = vtkActor::New(); 
 dsActor->SetMapper(dsmapper); 
 dsActor->GetProperty()->SetColor(0,1,0);

//The dsActor is empty as it doesn't show any points.

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