How to label model according to cell data?

I have model (*.vtu) containing several blocks like:

I want to label values on each block like:

How can I do it ? I can access values using:

vtkActor actor = ...;
var output = actor.GetMapper().GetInputAsDataSet();
var cell = output.GetCellData();
for (int i = 0; i < cell.GetNumberOfComponents(); i++)
    var cells = cell.GetArray(i);
    if (cells == null) continue;
    if ("IJK" != cell.GetArrayName(i)) continue; //There are many columns. I used IJK column as testing purpose
    var min = cells.GetRange()[0];
    var max = cells.GetRange()[1];
    for (int j = 0; j < nCells; j++)
        double val = cells.GetComponent(j, i);
        // how to label this value now ?
vtkDataSetMapper mapper = vtkDataSetMapper.New();

Here’s attached my model file: (3.1 MB)