[Paraview] vtk internals: vtkUnstructuredGrid versus vtkPolyData and vtkImageData

[David Doria]

On Sun, Nov 28, 2010 at 3:51 PM, Dan Lussier <dtlussier at gmail.com> wrote:
> I had a question about the nature of the underlying VTK data.
> In my work I am often visualizing particle data, which I currently have in
> XMDF files with Polyvertex topology.  When I load the files into PV, the
> data ends up being represented by a vtkUnstructuredGrid.  What is the
> difference between vtkUnstructuredGrid versus vtkPolyData?  I know that both
> inherit from abstract vtkPointSet so they are generally fairly
> interchangeable as most filters appear to require only a vtkPointSet.  Are
> there any filters that would take one but not the other?

vtkUnstructuredGrid allows you to have 3D (volumetric) cells, where
vtkPolyData only allow a maximum of 2D (polygonal) cells.

http://www.vtk.org/Wiki/VTK/Tutorials/3DDataTypes

> Some filters I am looking to use want a vtkPointSet input, but I have
> vtkImageData (via XMDF 3DCoRectMesh topology).  What would be the best way
> to make the conversion in Paraview?
> Many thanks.
> Dan Lussier

vtkImageDataGeometryFilter does this, but I don't see an interface for it in PV.

Here is an example of how to use it:
http://www.vtk.org/Wiki/VTK/Examples/Cxx/ImageData/ImageDataGeometryFilter

and here is how to make an existing VTK filter accessible in ParaView:
http://www.vtk.org/Wiki/Plugin_HowTo#Enabling_an_existing_VTK_filter

Good luck,

David