[vtkusers] How to get neighbors with vtkCellLinks ?

[Lloyd Fenelon]

Hello Jerome,

I know it's been a while but here's how I get the Ids
of the Delaunay neighbors for a point. I took inspiration
of the GetCellNeughbors() function from vtkUnstructuredGrid.

// Delaunay tessellation
delaunay = vtkSmartPointer<vtkDelaunay3D>::New();
delaunay->SetInput(profile);
delaunay->Update();


// build cells links
vtkSmartPointer<vtkCellLinks> cellLinks
                = vtkSmartPointer<vtkCellLinks>::New();

cellLinks = vtkSmartPointer<vtkCellLinks>::New();
cellLinks->Allocate(1000);
cellLinks->BuildLinks(delaunay->GetOutput());


// look for neighbors
numCells = cellLinks->GetNcells(i);
cells = cellLinks->GetCells(i);

-> for each point of Delaunay tessellation
    -> for each cell
        -> for each point in the cell
            if not the Delaunay point, let's look if it is a neighbor
            if first point of the first cell, store neighbor Id
            avoid redundancy
            store  neighbor Id

I hope this helps if the iterator you need is of that kind.

Lloyd




From: Jérôme [mailto:jerome.velut at gmail.com]
Sent: Wednesday, July 08, 2009 11:40 PM
To: Lloyd Fenelon
Cc: vtkusers at vtk.org
Subject: Re: [vtkusers] How to get neighbors with vtkCellLinks ?

Hi,

vtkDelaunay3D is an algorithm, whereas your question deals with data structures. You should investigate the GetCellNeighbors( ) member function from vtkUnstructuredGrid.
If you are allowed to use vtkPolyData, you can take a look at the sources of vtkSmoothPolyDataFilter, that I expect to compute a weighted sum over vertex neighbors.

Let us know if you solve or not your problem: I will have to implement this iterator soon.

'Hope that helps
Jerome
2009/7/8 Lloyd Fenelon <lfenelon at bccrc.ca<mailto:lfenelon at bccrc.ca>>

Hi,



I am using vtkCellLinks after computing a unstructured grid dataset

with vtkDelaunay3D. I would like to get the neighbors of each points.

Nothing comes out of the BuildLinks method the way I use it:



...

vtkSmartPointer<vtkDelaunay3D> delaunay
      = vtkSmartPointer< vtkDelaunay3D>::New();

computeDelaunay();

...



vtkSmartPointer<vtkCellLinks> cellLinks
      = vtkSmartPointer<vtkCellLinks>::New();



cellLinks->BuildLinks(delaunay->GetOutput());





Actually I don't know how to get back the points Ids

from delaunay so I give the unstuctured grid dataset.

Does someome can explain me what is going wrong here please ?

thank you



Lloyd













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