[vtkusers] Re: vtkThreshold Question

[Andrea Gavana]

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 <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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