[vtkusers] display a thick shell of volume

[Weiguang Guan]

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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