[vtkusers] Re: vtkThreshold Question

[John Platt]

Hi Andrea,

 

You can use vtkThreshold on any scalar field data by using
SelectInputScalars(). Add the threshold data to your UGrid using
AddArray() instead of SetScalars(). The properties you want to display
are added as the active scalars.

 

HTH

 

John.

 

-----Original Message-----
From: vtkusers-bounces+jcplatt=dsl.pipex.com at vtk.org
[mailto:vtkusers-bounces+jcplatt=dsl.pipex.com at vtk.org] On Behalf Of
Andrea Gavana
Sent: 31 March 2006 17:13
To: vtkusers at public.kitware.com
Subject: Re: [vtkusers] Re: vtkThreshold Question

 

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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