[vtkusers] Displaying a 3D SURFACE USING VTK

[N Smethurst]

Hi there again Ajit

You need to set up and connect your topology (vtkCellArray) otherwise
VTK has nothing to draw. The relevant bit of code in the example is:

    // Construct triangle strip topology.
    // The number of points in a cell is twice the number of columns.
    vtkIdType pnt[2*cols];
    // Loop for each row pair (the number of rows less one).
    for (int j=0; j<rows-1; j++) {
        count = 0;
        for (int i=0; i<cols; i++) {
            pnt[count++] = j*cols + i;
            pnt[count++] = (j+1)*cols + i;
        }
        surfCells->InsertNextCell(p,pnt);
    }

    surfPolyData->SetPoints(surfPoints);
    surfPolyData->SetStrips(surfCells);

You could construct this differently if you wanted, but triangle strips
are meant to be efficient.

Also, maybe its better to use a vtkPolyDataMapper than a vtkDataSetMapper.

Regards

Nick

Le Vendredi 13 Juin 2003 01:49, Ajit Rajwadé a écrit :
> Thanks. Okay here is what I tried, but when I run my program, i dont get
> anything on the display. What could be happening? Could you give me a
> hint?
>
> ===============================================================
>   vtkRenderer *renderer = vtkRenderer::New();
>   vtkRenderWindow *renWin = vtkRenderWindow::New();
>   renWin->AddRenderer(renderer);
>   vtkRenderWindowInteractor *iren = vtkRenderWindowInteractor::New();
>   iren->SetRenderWindow(renWin);
>
>   vtkPoints* surfPoints = vtkPoints::New();
>   vtkCellArray* surfCells = vtkCellArray::New();
>   vtkPolyData* surfPolyData = vtkPolyData::New();
>   vtkElevationFilter* surfElevation = vtkElevationFilter::New();
>   vtkPolyDataNormals* surfNormals = vtkPolyDataNormals::New();
>
>   fs = fopen (fileName,"r");
>   i = 0;
>   surfPoints->SetNumberOfPoints  (8000);
>   while (fgets (nextLine,100,fs))
>   {
>                // Basically reading x,y,z coordinates from a file.
> 	temp = (char*)strtok (nextLine," \n");
> 	point[0] = (float)(atof (temp));
>
> 	temp = (char*)strtok (NULL," \n");
> 	point[1] = (float)(atof (temp));
>
> 	temp = (char*)strtok (NULL," \n");
> 	point[2] = (float)(atof(temp));
>
> 	surfPoints->SetPoint(i,point);
> 	i = i + 1;
>   }
>
>
> surfPolyData->SetPoints(surfPoints);
>
> surfElevation->SetInput(surfPolyData);
> surfElevation->SetLowPoint(0.0, 0.0, 120);
> surfElevation->SetHighPoint(0.0, 0.0, 20); // For shading.
> surfNormals->SetInput(surfElevation->GetPolyDataOutput());
> surfNormals->SetFeatureAngle(80);
>
> vtkDataSetMapper *volMapper = vtkDataSetMapper::New ();
> volMapper->SetInput (surfElevation->GetOutput());
>
> vtkActor *volActor = vtkActor::New();
> volActor->SetMapper(volMapper);
>
> renderer->AddActor(volActor);
> renderer->SetBackground(1,1,1);
> renWin->SetSize(450,450);
>
> // interact with data
> renWin->Render();
> iren->Start();
>