[vtkusers] display a thick shell of volume

David Gobbi david.gobbi at gmail.com
Wed Oct 29 12:21:49 EDT 2014

Hi Weiguang,

There aren't any filters for combining vtkImageStencilData (there should
be!), so instead you will need to use two vtkImageStencil filters in
series: one for the first vtkImplicitFunctionToImageStencil output, and
then another for the second.

 - David

On Wed, Oct 29, 2014 at 10:09 AM, Weiguang Guan <guanw at rhpcs.mcmaster.ca>

>  Hi David,
> How to combine the outputs from two vtkImplicitFunctionToImageStencil
> instances as I need to use two spheres to define a shell? Thanks.
> Best,
> Weiguang
> On 28/10/2014 5:20 PM, David Gobbi wrote:
> Hi Weiguang,
>  You definitely want to avoid using vtkClipVolume before volume
> rendering, because it produces vtkUnstructuredGrid data instead of image
> data.
>  If you need a shell, you can use vtkImageGaussianSource to create an
> image of a Gaussian, and then threshold it with lower and upper thresholds
> to create a shell.  A Gaussian has radial symmetry, so thresholding will
> create a binary image of a spherical shell.   You can then multiply this
> shell by your image.
>  Or, instead of using vtkClipVolume, you can use
> vtkImplicitFunctionToImageStencil with vtkImageStencil.  The output will be
> a vtkImageData.  Or, for greater efficiency, use vtkROIStencilSource to
> create a spherical (ellipsoidal) stencil for vtkImageStencil.
>  Or, possibly the easiest "quick fix" would be to convert the
> vtkUnstructuredGrid that you already have into a vtkImageData by using
> vtkProbeFilter.  The vtkProbeFilter is a generic filter for copying (or
> interpolating) scalar data from one kind of data set onto another kind of
> data set.
>   - David
> On Tue, Oct 28, 2014 at 2:23 PM, Weiguang Guan <guanw at rhpcs.mcmaster.ca>
> wrote:
>> Hi VTK users,
>> I want to volume render (using 3D texture mapper) a shell with specified
>> thickness. Previously, I used vtkClipVolume twice, one clipped away the
>> inner portion of a regular volume data, the other clipped away outer
>> portion. The only problem is slow rendering speed because the resultant
>> data is no longer a regular volume data.
>> Can anyone suggest a better solution? Would it be faster if I used
>> several spheres with texture mapped on them and alpha-blending? Thanks.
>> Best,
>> Weiguang
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