[vtkusers] display a thick shell of volume

[David Gobbi]

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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