How to visualize cell attributes as labels - c++

Question

Solved: cxx file below is working as expected now. Thanks to #tomj as I used his ideas as well.
I have a data file (.vtk) file from which I read unstructured grid. How can I display cell attributes as labels?
cxx:
#include <vtkLookupTable.h>
#include <vtkCellData.h>
#include <vtkSmartPointer.h>
#include <vtkActor2D.h>
#include <vtkProperty.h>
#include <vtkDataSetMapper.h>
#include <vtkLabeledDataMapper.h>
#include <vtkUnstructuredGridReader.h>
#include <vtkUnstructuredGrid.h>
#include <vtkUnstructuredGridGeometryFilter.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include "vtkIdFilter.h"
#include "vtkCellCenters.h"
#include <iostream>
int main(int argc, char* argv[])
{
std::string inputFilename = argv[1];
// read file.
vtkSmartPointer<vtkUnstructuredGridReader> reader = vtkSmartPointer<vtkUnstructuredGridReader>::New();
reader->SetFileName(inputFilename.c_str());
reader->ReadAllScalarsOn();
reader->SetScalarsName(reader->GetScalarsNameInFile(0));
reader->Update();
unsigned int ncell = reader->GetOutput()->GetNumberOfCells();
// get attributes.
vtkSmartPointer<vtkUnstructuredGrid> ugrid = reader->GetOutput();
vtkSmartPointer<vtkCellData> cellData = ugrid->GetCellData();
vtkSmartPointer<vtkDataArray> data = cellData->GetScalars(reader->GetScalarsNameInFile(0));
// validate that attributes are read correctly.
for (int i=0; i<ncell; i++)
{
std::cout<< i << ": " << data->GetComponent(i,0)<< std::endl;
}
data = cellData->GetScalars(reader->GetScalarsNameInFile(1));
for (int i=0; i<ncell; i++)
{
std::cout<< i << ": " << data->GetComponent(i,0)<< std::endl;
}
data = cellData->GetScalars(reader->GetScalarsNameInFile(0));
// geometry filter.
vtkSmartPointer<vtkUnstructuredGridGeometryFilter> geometryFilter = vtkSmartPointer<vtkUnstructuredGridGeometryFilter>::New();
geometryFilter->SetInputConnection(reader->GetOutputPort());
geometryFilter->Update();
// Generate data arrays containing point and cell ids
vtkSmartPointer<vtkIdFilter> ids = vtkSmartPointer<vtkIdFilter>::New();
ids->SetInputConnection(geometryFilter->GetOutputPort());
ids->PointIdsOff();
ids->CellIdsOff();
ids->FieldDataOn();
// Create labels for cells
vtkSmartPointer<vtkCellCenters> cc = vtkSmartPointer<vtkCellCenters>::New();
cc->SetInputConnection(ids->GetOutputPort());
// lut
vtkSmartPointer<vtkLookupTable> lut = vtkSmartPointer<vtkLookupTable>::New();
lut->SetNumberOfTableValues(ncell);
lut->Build();
lut->SetTableValue(0, 1, 0, 0, 1); // red.
lut->SetTableValue(1, 0, 1, 0, 1); // green.
lut->SetTableValue(2, 0, 0, 1, 1); // blue.
// mapper.
vtkSmartPointer<vtkDataSetMapper> mapper = vtkSmartPointer<vtkDataSetMapper>::New();
mapper->SetInputConnection(geometryFilter->GetOutputPort());
mapper->SetLookupTable(lut);
mapper->SetScalarVisibility(1);
mapper->SetScalarModeToUseCellData();
mapper->SetScalarRange(11, 13);
mapper->GetInput()->GetCellData()->SetActiveScalars("cell_tag");
// label mapper.
vtkSmartPointer<vtkLabeledDataMapper> label_mapper = vtkSmartPointer<vtkLabeledDataMapper>::New();
label_mapper->SetInputConnection(cc->GetOutputPort());
label_mapper->SetLabelModeToLabelScalars();
// actor.
vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
actor->SetMapper(mapper);
actor->GetProperty()->SetRepresentationToWireframe();
// label actor.
vtkSmartPointer<vtkActor2D> label_actor = vtkSmartPointer<vtkActor2D>::New();
label_actor->SetMapper(label_mapper);
// renderer.
vtkSmartPointer<vtkRenderer> renderer = vtkSmartPointer<vtkRenderer>::New();
vtkSmartPointer<vtkRenderWindow> renderWindow = vtkSmartPointer<vtkRenderWindow>::New();
renderWindow->AddRenderer(renderer);
vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor = vtkSmartPointer<vtkRenderWindowInteractor>::New();
renderWindowInteractor->SetRenderWindow(renderWindow);
renderer->AddActor(actor);
renderer->AddActor(label_actor);
renderWindow->Render();
renderWindowInteractor->Start();
return EXIT_SUCCESS;
}
Datafile (.vtk):
# vtk DataFile Version 3.0
All in VTK format
ASCII
DATASET UNSTRUCTURED_GRID
POINTS 8 float
-20 0 0
-12.898 0 0
-7.65367 18.4776 0
-14.1421 14.1421 0
-18.4776 7.65367 0
-11.8832 4.95205 0
-9.03623 9.14123 0
-4.79931 11.937 0
CELLS 3 15
4 0 1 5 4
4 4 5 6 3
4 3 6 7 2
CELL_TYPES 3
9
9
9
CELL_DATA 3
SCALARS oga_cell_type int 1
LOOKUP_TABLE default
5
6
7
SCALARS cell_tag int 1
LOOKUP_TABLE default
11
12
13
Output:

Answer 1

See for example this tutorial, but it pretty much boils down to this:
mapper->SetLookupTable(lut); // lut is a lookup table for colors, see the linked tutorial or other vtk tutorials about look up tables
mapper->SetScalarVisibility(1);
mapper->SetScalarModeToUseCellData();
mapper->GetInput()->GetCellData()->SetActiveScalars("nameOfTheArrayToUseForColoringTheCells");