[vtkusers] some questions about cells, file formats, etc

[David Doria]

> I converted that file to vtkPolyData

How?

> and now I have a vtkPolyData file containing points (scalars)

Points are not scalars, they are vtkPoints. Scalars are usually
something like vtk*Array.

> and vertices. From what I know, those vertices serve to represent topology,
> the cells.

Correct.

> So, how were the vertices defined from the points I already had on the wrl file? Where they generated randomly?

They should be a one to one mapping, ordered, to the points.

> And, if the vertices are related to cells, there shouldn't be defined the attribute data related to cells (cell_data)? Or is it represented implicitly?

The scalars can either be defined on the points (vtkPointData) or
cells (vtkCellData). It would be the same result if you only have 0D
cells (vertices).

> 2)After converting the wrl file to vtkPolyData, I applied a set of filters
> and I got an Unstructured Grid. Before writing any output I selected a set
> of points and containing cells from the unstructured grid and I converted
> them to vtkPolyData: The resulting vtkPolyData file contains points (scalars), vertices,
> cell_data and field_data. Why do I have cell_data and field_data explicitly represented in the output file?

What is in the cell/field data? You can inspect it in ParaView.

> Both cell_data and field_data were already defined in the input file, right?
> And, (sorry for so many questions) what exactly is field_data?

Hopefully this paragraph answers some of your questions;
http://www.vtk.org/Wiki/VTK/Examples/Cxx/PolyData/FieldData

David