[vtkusers] vtkDelauany2D triangulation--But where are the triangles????

[Sylvain Jaume]

Hi Dhaniram Kshirsagar,

vtkDelaunay2D takes points at its input, and gives triangles at its ouput.
Read http://www.vtk.org/doc/nightly/html/classvtkDelaunay2D.html
More information in the VTK book:
http://www.kitware.com/products/vtktextbook.html

You may find this code snippet useful:

vtkPoints *newPoints = vtkPoints::New();
newPoints->InsertNextPoint( 0, 0, 0 );
newPoints->InsertNextPoint( 1, 0, 0 );
// create more points

vtkPolyData *polyData = vtkPolyData::New();
polyData->SetPoints( newPoints );
newPoints->Delete();

vtkDelaunay2D *delaunay2D = vtkDelaunay2D::New();
delaunay2D->SetInput( polyData );
polyData->Delete();
delaunay2D->Update();

int npts, *pts;

delaunay2D->GetPolys()->InitTraversal();

while ( delaunay2D->GetPolys()->GetNextCell( npts, pts ) )
{
    cout << "points in the triangle: " << pts[0] << " " << pts[1] << " " 
<< pts[2] << "\n";
}

Cheers,
Sylvain

Dhaniram Kshirsagar wrote:

> Hi Sylvain,
>  
> ---->>>>>Do you mean that you get the input triangles at the output?
> Yes I made some sequential polys like this...
>  
>  int numPts = Points->GetNumberOfPoints();
>  for( int idx=0; idx< numPts; )
>  {
>   int nPoly[3];
>   nPoly[0] = idx;
>   nPoly[1] = ++idx;
>   nPoly[2] = ++idx;
>   *vtkPolys*->InsertNextCell( 3, nPoly );
>  }
>  
> *vtkPolys --> input to vtkPolyData which already contains the vtkPoints.*
> **
> ---->>>>>You do not need to set the polys.
>  
> You mean to say I need to input *only points* 
> (vtkPoints->vtkPolyData->vtkDelaunay2D)?
> and i will get the triangles at output? no cellarray for polys?
>  
> If yes please let me know the code snippet for the same which will 
> take points and will result in polys(triangles).
>  
> Thanks for the reply.
>  
> Thankx
>
>  
> 2005/11/5, Sylvain Jaume <sylvain.jaume at kitware.com 
> <mailto:sylvain.jaume at kitware.com>>:
>
>     Hi Dhaniram Kshirsagar,
>
>     Do you mean that you get the input triangles at the output?
>     You do not need to set the polys.
>
>     Cheers,
>     Sylvain
>
>     Dhaniram Kshirsagar wrote:
>
>     > Hi Sylvain,
>     >
>     > After setting the vtkcellarray(for polys) in vtkpolydata (which is
>     > input to the delaunay2d), Now I am able to get the triangles.
>     >
>     > Thankx
>     >
>     >
>     > 2005/11/4, Sylvain Jaume <sylvain.jaume at kitware.com
>     <mailto:sylvain.jaume at kitware.com>
>     > <mailto:sylvain.jaume at kitware.com
>     <mailto:sylvain.jaume at kitware.com>>>:
>     >
>     >     Hi Dhaniram Kshirsagar,
>     >
>     >     You don't need to use delaunay->SetSource().
>     >     Use it only if you want constrained Delaunay.
>     >
>     >     Cheers,
>     >     Sylvain
>     >
>     >     Dhaniram Kshirsagar wrote:
>     >
>     >     > Hi,
>     >     >
>     >     > I searched the entire mail archive for answer to my
>     problem, but
>     >     found
>     >     > only problems no solutions to them.
>     >     >
>     >     > My problem is, I have input points in the form of x, y and
>     z (large
>     >     > numbers(double type)) and i want the output as the set of
>     triangles,
>     >     > however i am getting only the
>     >     > vertics.
>     >     >
>     >     > Here is the code snippet that i am using to get the output
>     as set of
>     >     > triangles.
>     >     >
>     >     > vtkDelaunay2D* pDelny = vtkDelaunay2D::New( );
>     >     > vtkPolyData* pPointSet = vtkPolyData::New( );
>     >     > vtkPoints* pPoints = vtkPoints::New( );
>     >     >
>     >     >                 //collects the points i.e. x , y, and z
>     >     > GetPoints( pPoints );
>     >     >
>     >     > pPointSet->SetPoints( pPoints );
>     >     >
>     >     > //now generate the vtk file
>     >     > vtkPolyDataWriter* writer = vtkPolyDataWriter::New();
>     >     > writer->SetFileName( "c:\\earth.vtk");
>     >     > writer->SetInput( pPointSet );
>     >     > writer->Write(); //throws an exception
>     >     > writer->Update();
>     >     >            *    /***the generated vtk file contains the
>     only one
>     >     fixed
>     >     > value***/
>     >     >               ///However i am not usig this file
>     >     > *
>     >     > pDelny->SetTolerance( 0.001 );
>     >     > //pDelny->SetBoundingTriangulation(1);
>     >     > pDelny->SetAlpha( 1 );
>     >     > //pDelny->BoundingTriangulationOff();
>     >     > //pDelny->SetOffset( 1000 );
>     >     >
>     >     > pDelny->SetInput(pPointSet);
>     >     > pDelny->SetSource( pPointSet );
>     >     > pDelny->Update();
>     >     >
>     >     >
>     >     >  vtkPolyData* pVtkData = pDelny->GetOutput( );
>     >     >  int nsize = pVtkData->GetNumberOfCells(); //returned the
>     same
>     >     number
>     >     > as the number of points
>     >     >  vtkCellArray* cellPol = pVtkData->GetPolys(); //zero returned
>     >     >  int numpol = cellPol->GetNumberOfCells();
>     >     >  vtkCellArray* cellVert = pVtkData->GetVerts();
>     >     >  int numver = cellVert->GetNumberOfCells(); //returned the
>     same
>     >     number
>     >     > as the number of points
>     >     >
>     >     >  nCells = pVtkData->GetNumberOfPolys();
>     >     >  nCnt3 = pVtkData->GetNumberOfVerts(); //returned the same
>     number as
>     >     > the number of points
>     >     >
>     >     > But where are the triangles????
>     >     >
>     >     > Now through pDelny->GetOutput I am expecting set of
>     triangles in
>     >     > vtkPolyData object.
>     >     > Am I right?
>     >     >
>     >     > Thanks
>     >     >
>     >    
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