[vtkusers] Volume Render

[Darshan Pai]

On Fri, May 7, 2010 at 3:12 AM, Darshan Pai <darshanpai at gmail.com> wrote:

> I was trying most of the volume render functionality . I just wanted some
> input on this effect I see.
>
> I threshold  a volume dataset between 400 - 699 using vtkImageThreshold.
> InValue set at 255 , out value set at 0
>
> I feed this to the VolumeRaycastMapper. The function is set to a
> vtkVolumeRayCastCompositeFunction.
>
> In the property I set the opacity as follows
>  vtkPiecewiseFunction *oTFun2 = vtkPiecewiseFunction::New();
>   oTFun2->AddSegment(  10, 0.0, 200, 1);
>   oTFun2->AddSegment(  200, 1, 201, 0);
>
> This means that all scalar values higher than 201 should be clamped to
> opacity 0 . Since the threshold volume has only 2 values 255 and 0 , the
> output should be a blank screen . But I see some volume structures .
>
> The question is why do I see volume elements even though the opacity for 0
> and 255 are both at 0 ?
>
> Regards
> Darshan
>
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