[vtkusers] Using vtkPolyDataReader with vtkClipPolyData

[Alan Smithee]

Hi Chris!

A plane is defined by three points and that is what you have. Take two 
of them and make the cross product, since the cross product is a vector 
which is orthogonal to both. In principal this cross product vector is 
the normal.

Or you use the static function ComputeNormal of vtkTriangle:

             double P1[3] = { p1[0], p1[1], p1[2] };
             double P2[3] = { p2[0], p2[1], p2[2] };
             double P3[3] = { p3[0], p3[1], p[2] };

             double n[3];
             vtkTriangle::ComputeNormal(P1, P2, P3, n);

Am 16.02.2012 23:59, schrieb Bayliss, Chris (Chicago):
>
> Hi,
>
> I am having trouble extracting the appropriate data from a .vtk 
> polydata file and using it with vtkClipPolyData.  My polydata file 
> contains three points representing a plane, the file contents are 
> shown below.
>
> _(Sample1-plane.vtk)___
>
> # vtk DataFile Version 3.0
>
> vtk output
>
> ASCII
>
> DATASET POLYDATA
>
> POINTS 3 float
>
> -2.31291 -0.472235 -26.3682 27.227 -13.8288 4.74193 -29.2774 -4.23973 
> -2.38224
>
> VERTICES 3 6
>
> 1 0
>
> 1 1
>
> 1 2
>
> I am not sure how to read/extract this data and convert it into a 
> usable form for the vtkclipPolyData filter.  My code is below.  Does 
> anyone know how to compute the origin and normal vector form the 
> polydata file above?
>
> //import polydata file from above:
>
> vtkPolyDataReader *trim =vtkPolyDataReader::New();
>
>    trim->SetFileName("C:/Program Files/VTK/TPS/Debug/Sample1-plane.vtk");
>
>    trim->Update();
>
> //Convert vtkpolydatareader object to vtkpolydata
>
>    vtkPolyData* trimpd = trim->GetOutput();
>
>    trimpd->SetPoints(trim->GetOutput()->GetPoints());
>
>    trimpd->SetVerts(trim->GetOutput()->GetVerts());
>
>    trimpd->SetPolys(trim->GetOutput()->GetPolys());
>
>    trimpd->Update();
>
> // Write all of the coordinates of the points in the vtkPolyData to 
> the console.
>
> for(vtkIdType a = 0; a < trimpd->GetNumberOfPoints(); a++)
>
>       {
>
> double p[3];
>
>       trimpd->GetPoint(a,p);
>
> // This is identical to:
>
> // polydata->GetPoints()->GetPoint(i,p);
>
>       std::cout << "Points in trim plane " << a << " : (" << p[0] << " 
> " << p[1] << " " << p[2] << ")" << std::endl;
>
>       }
>
> //Compute plane normal
>
>    vtkPolyDataNormals *trimnorm = vtkPolyDataNormals::New();
>
>    trimnorm->SetInput(trimpd);
>
>    trimnorm->ComputePointNormalsOn();
>
>    trimnorm->ComputePointNormalsOn();
>
>    trimnorm->ComputeCellNormalsOn();
>
>    trimnorm->Update();
>
> /*trimpd->GetCellData()->SetNormals(trimnorm->ComputeCellNormalsOn()->GetOutput());*/
>
>    
> trimpd->GetCellData()->SetNormals(trimnorm->GetOutput()->GetCellData()->GetNormals());
>
>    trimpd->Update();
>
> ///////// Get cell normals ///////////
>
>   vtkDoubleArray *cellNormalsRetrieved = 
> vtkDoubleArray::SafeDownCast(trimpd/*->GetOutput()*/->GetCellData()->GetNormals());
>
> if(cellNormalsRetrieved)
>
>     {
>
>     cout << "There are " << cellNormalsRetrieved->GetNumberOfTuples() 
> << " cell normals." << endl;
>
> for(vtkIdType i = 0; i < cellNormalsRetrieved->GetNumberOfTuples(); i++)
>
>       {
>
> double cN[3];
>
>       cellNormalsRetrieved->GetTuple(i, cN);
>
>       cout << "Cell normal " << i << ": " << cN[0] << " " << cN[1] << 
> " " << cN[2] << endl;
>
>       }
>
>     }
>
> else
>
>     {
>
>     cout << "No cell normals." << endl;
>
>     }
>
> //Create trim plane from polydata:
>
> vtkPlane *trimplane = vtkPlane::New();
>
>    trimplane->SetOrigin(trimpd->GetPoint(0));
>
>    trimplane->SetNormal(0.0, 1.0, 0.0);//made up values, would like to 
> use output of vtkpolydatanormals somehow.
>
> //clip polydata named "warp":
>
>    vtkClipPolyData *clipper = vtkClipPolyData::New();
>
>    clipper->SetInputConnection(warp->GetOutputPort());
>
>    clipper->SetClipFunction(trimplane);
>
>    clipper->GenerateClippedOutputOn();
>
>    clipper->SetValue(0.5);
>
> Thanks,
>
> Chris
>
>
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