[vtkusers] Re: vtkThreshold Question

[Amy Squillacote]

Hi Andrea,

You can apply vtkExtractCells to your already-built 
vtkUnstructuredGrid because vtkUnstructuredGrid is a subclass of vtkDataSet.

- Amy

At 11:12 AM 3/31/2006, Andrea Gavana wrote:
>Hello Goodwin,
>
>     thank you very much for your help. It seems to me (if I have 
> read correctly the doc), that vtkExtractCells requires a 
> vtkDataSet, a file in other words... is that correct?
>Well, I already have a vtkUnstructuredGrid built by reading an 
>external file (not VTK format). The idea of extracting cells based 
>on Ids implemented in vtkExtractCells is very promising... there is 
>nothing similar but without using a vtkDataSet?
>The problem is, I should be able to filter out cells by certain 
>criteria: for example, at the moment I am trying to exclude inactive 
>cells using this ACTNUM, but I would like to be able to filter out 
>the cell based on, i.e., cell centroid depth, cell permeability, 
>cell saturations and so on. This seems to me something like a 
>vtkFilter*, and if every time I set up a new filter I have to create 
>a file and re-read it I will end up in doing slow things. I am too 
>newbie to browse in the right doc places...
>
>Thank you very much for your suggestions.
>
>Andrea.
>
>
>On 3/31/06, Goodwin Lawlor 
><<mailto:goodwin.lawlor at ucd.ie>goodwin.lawlor at ucd.ie> wrote:
>Andrea Gavana wrote:
> > Hello NG,
> >
> >     sorry if this question is simple, but I have searched over the web
> > and I have't found anything close to what I should so. Basically, I have
> > a vtkUnstructuredGrid in which I set the cell data using some property.
> > By switching with a wxPython radiobutton I can change on the fly the
> > property displayed on the grid (like permeability, saturation, cell
> > centroids and so on). Well, my group of data has also a property called
> > "ACTNUM", that tells which cells are active (ACTNUM=1) and which are not
> > active (ACTNUM=0). Active cells should be displayed while inactive cells
> > should be hidden.
> > I have succeeded to use vtkThreshold to filter out inactive cells, but
> > only when I set cell_data=ACTNUM, using something like:
> >
> > grid.GetCellData().SetScalars(ACTNUM)
> >
> > What I would like to do is, whatever property is displayed on screen, to
> > hide inactive cells based on ACTNUM value. For example, I would like to
> > display cell centroids property on the grid filtering out inactive
> > cells. Something like:
> >
> > grid.GetCellData().SetScalars(Whatever)
> > ??? Apply threshold on grid using ACTNUM ???
> >
> > Is there a way to do this?
> >
> > Thank you very much for your help and suggestions.
> >
> > Andrea.
>Hi Andrea,
>
>You could try vtkExtractCells to filter out cells. You would have to
>loop through ACTNUM and create the appropriate vtkIdList to apply to the
>filter. Alternatively, you could try to convert your scalars to RGBA
>values, where ACTNUM determines the A value (the opacity).
>
>hth
>
>Goodwin
>
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