[vtkusers] display a thick shell of volume

Weiguang Guan guanw at rhpcs.mcmaster.ca
Wed Oct 29 13:00:10 EDT 2014

Thanks again, David, have a great day!


On 29/10/2014 12:21 PM, David Gobbi wrote:
> 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 <mailto:guanw at rhpcs.mcmaster.ca>> wrote:
>     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 <mailto: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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