[vtkusers] performance issue

[David Gobbi]

Hi Vincent,

You are probably running in to the same problem that I was discussion
in another thread: the centre of your top and bottom voxels lie
exactly at the top or bottom of your element, so slight numerical
errors in either direction can cause them to be inside or outside.

I'm not sure why you would decrease the tolerance in this situation...
if a filter isn't giving the desired results, your first instinct
should usually be to _increase_ the tolerance.  But as you mentioned,
the tolerance doesn't do much in the Z direction anyway.

The only thing that I can think of is for you to take your generated
polydata and give it a slight vertical stretch, i.e. to add an
artificial tolerance in the Z direction.

 - David


On Thu, Feb 24, 2011 at 3:50 PM, vlibertiaux <vlibertiaux at gmail.com> wrote:
>
> Hi David,
>
> Thanks to your good advice, my program is running 4 times faster now !
>
> However, I still have a little problem with the vtkDataSetSurfaceFilter and
> vtkPolyDataToImageStencil:
>
> the outmost z values  (0 and 124) of my volume are considered outside the
> element and thus affected the background value while they shouldn't.
>
> I checked the PolyData structure and the bounds are the same than the
> element's and the PolyDataToImageStencil has the good extent.
>
> I set the Tolerance of the PDTIS to a very low value but it changed nothing.
> It is said in the documentation that it is not used in the z direction but
> my test element is a regular hexaedron, so there should not be fraction of
> voxel in or out to be considered.
>
> Do you have any idea why the top and the bottom of my volume are set to the
> background value ?
>
> Best regards,
>
> V.
> --
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