Changing the scalar value of a region

[Charles Law]

<x-flowed>Ron,

You can use vtkPolyDataConnectivity after the marching-cubes filter
to select which surface you want.

There is also the filter vtkImageSeedConnectivity, but unfortunately it
only works with binary/unsigned-char data.  What you suggest is possible:

reader
  |      |
  |    vtkImageThreshold (threshold higher than iso value)
  |      |
  |    vtkImageSeedConnectivity
  |      |
vtkImageMask
        |
vtkContourFilter

...

Charles.
At 10:50 PM 8/10/99 +0300, Ron Inbar wrote:
>Hello all!
>
>I have a stack of CT scans of someone's chest.  I'm trying to extract a
>model of the lungs using Marching Cubes.  I use a low threshold value to
>detect the boundary between air and anything denser than air.  This way I
>get the lungs all right, but I also get the outer surface of the man's body.
>I was thinking about the following approach to get rid of this unwanted
>surface: take a point known to be outside the body, and proceed by
>connectivity to identify the region of air surrounding the body.  Then
>change the scalar value of every point in this region to something higher
>than the threshold.  Marching Cubes can take it from here.
>
>What filter(s) should I use to do this?  I saw that vtkConnectivityFilter
>can identify the region, but how can I use it to obtain a
>vtkStructuredPoints with the same dimensions as the original volume, but
>with different scalars?
>
>Your help will be greatly appreciated,
>
>Ron
>
>
>
>
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</x-flowed>