[vtkusers] VTKboolean smoothes the results! Any other libraries for boolean operation on polydata?

Tue Jul 18 10:26:02 EDT 2017

Okay, let's try one more thing. Does

vtkDataArray* normals = output->GetPointData()->GetArray("Normals");

return NULL? Perhaps the normals array is being copied but not being set as
the active normals.

Thanks,
Cory

On Tue, Jul 18, 2017 at 9:03 AM, Majid Mohammad sadeghi <
majid.msadeghi at yahoo.com> wrote:

> Dear Cory,
>
> !normals returns true, so as you said there is no normal array. Is there a
> way to copy that before the operation and apply it afterwards? But I think
> that wont work because part of the data is changed in the boolean
> operation. So how can we keep the normals?
>
> Thanks,
>
>
> On Tuesday, July 18, 2017, 4:21:45 PM GMT+3, Cory Quammen <
> cory.quammen at kitware.com> wrote:
>
>
> Hmm, now I wonder if the boolean operations filter is simply removing the
> normals filter. The code has changed from the original, which did preserve
> normals. It looks like the current code should preserve normals as well,
> but I'm not 100% sure if that is the case.
>
> In the output of the boolean operation filter, could you check that there
> is a normals array in the pointdata?
>
> vtkDataArray* normals = output->GetPointData()-> GetNormals();
>
> If "normals" is NULL, then the normals are not being copied to the output.
>
> Thanks,
> Cory
>
>
>
> On Mon, Jul 17, 2017 at 11:47 AM, Majid Mohammad sadeghi <
> majid.msadeghi at yahoo.com> wrote:
>
> Dear Cory,
>
> All you said was exactly what I have done. I tested your method to check
> the data and I could see only one of the objects. So If I understand right,
> during the boolean operation the vtkPolyDataNormals are recalculated and
> that is the reason the polydata is shown smoothed. Is there a way not to
> let boolean recalculate it? Or more generally is there a way to keep the
> bumps. That kind of is the norm in the medical field and some doctors might
> not feel very good about the smooth data.
>
> Thanks.
>
>
>
>
>
> On Monday, July 17, 2017, 7:33:19 PM GMT+3, Cory Quammen <
> cory.quammen at kitware.com> wrote:
>
>
> What I think you are seeing with the rough surface is surface normals
> generated from an image volume. I am assuming a lot here, so please correct
> me if I am wrong. It looks like you have a geometry of a bone extracted
> from a CT scan. The extraction algorithm was probably a variant of marching
> cubes or a similar algorithm. The surface normals estimated from the
> surface extraction algorithm were probably computed from the intensity
> gradient of the CT scan. This is a reasonable approach, but noise in the CT
> scan will affect the gradient calculation and may perturb the surface
> normals in the geometry a little. When this happens, you can get a rough
> appearing surface from the surface lighting calculation. Google "bump
> mapping" for how this can be used for a nice graphics effect - I think
> roughly the same thing is happening with your original data.
>
> When you use vtkPolyDataNormals, the normals are computed from the surface
> data, which was smooth to begin with. Hence, the normals are not perturbed,
> so you don't get a bumpy appearance.
>
> In any case, the measurements you want to take are not dependent on the
> surface normals. As long as the points on the surface are not smooth, which
> they should not be, your measurement procedure should be fine.
>
> To convince yourself the geometry is the same, you can display both the
> original "bumpy" surface and the smoothed surface at the same time with
> different colors. You should see just one surface or the other, probably
> the one you added to the vtkRenderer last. If the geometry is different,
> you will see some of one surface color and some of the other depending on
> which geometry is closer to the camera. I suspect you will see just one
> surface.
>
> HTH,
> Cory
>
> On Mon, Jul 17, 2017 at 11:22 AM, Majid Mohammad sadeghi <
> majid.msadeghi at yahoo.com> wrote:
>
> Dear Cory,
>
> As I applied vtkPolyDataNormals to the polydata before the boolean
> operation I got the smoothed object, so you were right. But I dont
> understand exactly what is happening here? Since the geometry dimentions
> are very important for my application, Can I have the noisy version? Is
> there any way I do not get it smoothed?
>
> Thanks,
>
>
>
>
> On Monday, July 17, 2017, 6:48:58 PM GMT+3, Cory Quammen <
> cory.quammen at kitware.com> wrote:
>
>
> There shouldn't be any geometry smoothing going on in this filter. Can you
> verify that the geometry has changed in the smoothed version?
>
> This is speculation, but one possibility is that the surface normals in
> your original surface come from a gradient computation in the volume from
> which the surface was extracted and noise in the volume result in the bumpy
> appearance. You can check this by applying the vtkPolyDataNormals filter to
> your original surface and looking at the result.
>
> HTH,
> Cory
>
> On Mon, Jul 17, 2017 at 10:21 AM, Majid Mohammad sadeghi <
> majid.msadeghi at yahoo.com> wrote:
>
> Dear Cory,
>
> Thanks for the reply, I set the actors property to  SetInterpolationToFlat
> (); as you said, but the result is the same I put a picture before and
> after boolean operation here. Any suggestion? Are you familier with any
> other library? Current boolean operation takes about 150 seconds on my
> system, do you think this is normal?
>
> [image: Inline image]
>
>
>
>
> On Monday, July 17, 2017, 6:00:50 PM GMT+3, Cory Quammen <
> cory.quammen at kitware.com> wrote:
>
>
> What do you mean by smooth? The lighting is smooth? I think the filter
> may be adding surface normals, in which case any actor for the data
> will turn on Gouraud shading (or maybe Phong) by default, which will
> make your surface look smooth. You can turn off smooth lighting as
> shown in this example:
>
> http://www.vtk.org/Wiki/VTK/ Examples/Cxx/Visualization/ FlatShading
> <http://www.vtk.org/Wiki/VTK/Examples/Cxx/Visualization/FlatShading>
>
> On Mon, Jul 17, 2017 at 9:49 AM, Majid Mohammad sadeghi via vtkusers
> <vtkusers at vtk.org> wrote:
> > Hi everyone,
> >
> > I am using vtkBooleanOperationPolyDataFil ter, and it works fine except
> after
> > the operation it smoothes the polydata, which I dont want. Is there a
> way to
> > stop that? Or is there another library for boolean operations on
> polydata?
> >
> > Thanks.
> >
> >
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>
> --
> Cory Quammen
> Staff R&D Engineer
> Kitware, Inc.
>
>
>
>
> --
> Cory Quammen
> Staff R&D Engineer
> Kitware, Inc.
>
>
>
>
> --
> Cory Quammen
> Staff R&D Engineer
> Kitware, Inc.
>
>
>
>
> --
> Cory Quammen
> Staff R&D Engineer
> Kitware, Inc.
>

-- 
Cory Quammen
Staff R&D Engineer
Kitware, Inc.
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