[vtkusers] Question about the meaning of the text file generated by vtkPolyDataWriter, which is for reading a vtkPolyData

[HayamiSanjuro]

Hi guys,

I found I have a difficult to understand the text file generated by vtkPolyDataWriter.

The situation is I create a set of following 5 points to construct a ploygon:

vtkPoints *points = vtkPoints::New();
    points->InsertPoint(0,0,0,0);
    points->InsertPoint(1,2,2,0);
    points->InsertPoint(2,4,2,0);
    points->InsertPoint(3,6,0,0);
    points->InsertPoint(4,3,1,0);
vtkCellArray *polys = vtkCellArray::New();
    polys->InsertNextCell(5);
    polys->InsertCellPoint(4);
    polys->InsertCellPoint(3);
    polys->InsertCellPoint(2);
    polys->InsertCellPoint(1);
    polys->InsertCellPoint(0);

Then, i performed the constrained Delaunay triangulation:
vtkPolyData *polyData = vtkPolyData::New();
    polyData->SetPoints(points);
    polyData->SetPolys(polys);
vtkDelaunay2D *del = vtkDelaunay2D::New();
    del->SetInput(polyData);
    del->SetSource(polyData);

At last, I tried to see the result of the triangulation by get the output and write the result polygon to a text file by using vtkPolyDataWriter 

vtkPolyData * outputPolyData = del->GetOutput();
    outputPolyData->Update();
    vtkPolyDataWriter *writer = vtkPolyDataWriter::New();
    writer->SetInput(outputPolyData);
    writer->SetFileName("test.txt");
    writer->Write();

The result text file is pretty confusing me:
----text.txt----------------------------------------
# vtk DataFile Version 3.0
vtk output
ASCII
DATASET POLYDATA
POINTS 5 float
0 0 0 2 2 0 4 2 0 
6 0 0 3 1 0 
POLYGONS 3 12
3 4 2 1 
3 4 3 2 
3 4 1 0 

CELL_DATA 3
POINT_DATA 5
------------------------------------------------------
I can see the "POINTS 5 float" section is state the coordinate of 5 points
but the "POLYGONS 3 12" really confused me. Can any1 explain it for me PLZ!!!!!!!!!

Cheers! 

YANG Rong 

20 Orton,
Glenfield, AKL, 
New Zealand 

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