[vtkusers] How do I get the scalar value of polygons created in a section?

[Philip Morris Jones]

Hi

I want to use VTK as an engine and render the output using another
technique. I have found out how to extract the polygon data but cannot seem
to find the scalar value. The best I can do at the moment is to redner using
a black to whire colour scale and find the colour of the points and use
this, but this gives me only a value from 0 to 255 which is too coarse. Can
anybody help?

Thanks

I have modified and written some examples to get to this C++ code:


//
// read in a .vtk file and create a section plot
//

// first include the required header files for the vtk classes we are using


#include "vtkUnstructuredGridReader.h"
#include "vtkRenderWindow.h"
#include "vtkGeometryFilter.h"
#include "vtkPolyDataMapper.h"
#include "vtkRenderWindowInteractor.h"
#include "vtkCutter.h"
#include "vtkDataSetAttributes.h"
#include "vtkCellDataToPointData.h"


int main( int argc, char *argv[] )
{
 // create an unstructuredgridreader

 vtkUnstructuredGridReader* ProMeshC = vtkUnstructuredGridReader::New();
 char fname[256];
 sprintf(fname,"tut2.vtk");
 ProMeshC->SetFileName(fname);
 // force a read
 ProMeshC->Update();

 vtkCellDataToPointData* ProMesh = vtkCellDataToPointData::New();
 ProMesh->SetInput( ProMeshC->GetOutput() );

 // section cut

 vtkLookupTable *lut1 = vtkLookupTable::New();
 lut1->SetHueRange(0, 0.0);
    lut1->SetSaturationRange(0, 0);
    lut1->SetValueRange(0, 1);

 vtkPlane* cutplane = vtkPlane::New();
    cutplane->SetOrigin(0,0,-.01);
    cutplane->SetNormal(0,0,1);

 vtkCutter* planeCut = vtkCutter::New();
    planeCut->SetInput( ProMesh->GetOutput() );
    planeCut->SetCutFunction(cutplane);

 vtkPolyDataMapper* cutMapper = vtkPolyDataMapper::New();
    cutMapper->SetInput ( planeCut->GetOutput() );
 cutMapper->SetScalarRange ( 0, 20 );
 cutMapper->SetLookupTable( lut1 );

 vtkActor *cutActor = vtkActor::New();
    cutActor->SetMapper( cutMapper );

 // get poly data
 cutActor->GetMapper()->GetInput()->Update();
 vtkPolyData *polyData = (vtkPolyData *) cutActor->GetMapper()->GetInput();
 vtkUnsignedCharArray *colorArray = cutActor->GetMapper()->MapScalars(1.0);

 // get primitive arrays
 vtkCellArray *polys;
 polys = polyData->GetPolys();

 int numPolys = polys->GetNumberOfCells();
 cerr << " " << numPolys << " polys";
 cerr.flush();

 int i, prim = 0, vert = 0;
 int npts, *pts;

 for (polys->InitTraversal(); polys->GetNextCell(npts, pts); prim++)


  for (i=0; i < npts; i++)
  {
   float *aVertex = polyData->GetPoint(pts[i]);
   cout << "v mxv " << aVertex[0] << " " << aVertex[1] << " " <<  aVertex[2]
<< "\n";
   unsigned char *aColor = colorArray->GetPointer(pts[i]);
   cout << (int) aColor[0] << "\n";
  }
  if(npts==3)
  {
   cout << "c mxv - 1 mxv - 2 mxv - 3 mxv - 3\n";
  }
  else
  {
   cout << "c mxv - 1 mxv - 2 mxv - 3 mxv - 4\n";
  }
 }


 vtkRenderer *ren1 = vtkRenderer::New();
 vtkRenderWindow *renWin = vtkRenderWindow::New();
 renWin->AddRenderer(ren1);

 // an interactor
 vtkRenderWindowInteractor *iren = vtkRenderWindowInteractor::New();
 iren->SetRenderWindow(renWin);
 ren1->AddActor(cutActor);
 ren1->SetBackground(1,1,1); // Background color white

 // render an image (lights and cameras are created automatically)
 renWin->Render();

 // begin mouse interaction
 iren->Start();

 return 0;
}






philip at cd.co.uk