[vtkusers] Surface - Volume intersection

[David.Pont at ForestResearch.co.nz]

Hi Donald,
   I am pretty sure the answer is no, but...
I have developed a C++ class that treats polydata as an implicit surface,
thus allowing clipping and cutting in vtk. The algorithm is actually quite
brain-dead and is not a 'correct' approach. But it does work just fine in
many cases. I almost started down the path of making a correct algorithm,
but it is quite a big job and I just dont have that much spare time. This
(boolean operations on polydata) would be a very useful addition to vtk.

Now some questions: your pit sounds like it can be loaded into vtk as
polydata, but I am not clear about the 'volume'. In vtk a volume is a
regular 3D grid of data. Is the ore body a true vtk volume, or do you have
a 3D surface (closed, or not) defining the ore body, ore=polydata? If the
ore body is a true volume you can contour it to get a polydata surface.

Given two polydata surfaces (pit and ore) you could try my class to get the
intersection.

- input ore surface to my class vtkImplicitPolydata
- input the pit surface to vtkClipPolydata, and specify the
vtkImplicitPolydata (ore) as the implicit function, and set value to 0 (the
default)

This should spit out chunks of pit surface that are 'inside' the ore
surface.
You can use SetInsideOut on the vtkClipPolydata, and change which surface
is clipped to get different parts of the two surfaces.

Note you can use vtkMassProperties to get area and volume from polydata.

  let me know if you want the code. I make no promises about results! but
if the surfaces are not too 'wrinkled', it can work OK.

  regards
    Dave Pont




                                                                                                                                                  
                    Donald S Dunbar                                                                                                               
                    <dsd at lorax.ca>         To:     vtkusers at public.kitware.com                                                                    
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                    vtkusers-admin at w       Subject:     Re: [vtkusers] Surface - Volume intersection                                              
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                    20/06/2003 06:44                                                                                                              
                                                                                                                                                  
                                                                                                                                                  




Okay, no bites on this one.  Can I at least get some indication from
someone about whether this is within the realm of possible VTK tricks?
Are there any classes for extracting the intersection between volumes
and surfaces?

Many thanks,
D. Dunbar

On Monday, June 16, 2003, at 04:58 PM, Donald S Dunbar wrote:

> I have an irregular surface in 3D (an open pit mine) and a volume that
> intersects this surface (an ore body).  I would like to calculate the
> area of the surface corresponding to the intersection.  The volume is
> also irregular, hence the intersection may consist of multiple patches
> of the surface.  Can this be done using VTK?  How?
>
> Thanks,
>
> Donald S. Dunbar, Ph.D.
> Senior Physical Oceanographer
> Lorax Environmental Consultants Ltd.
> 1108 Mainland Street
> Vancouver, BC  V6B 5L1
>
> Ph: 604-688-7173
> Fx: 604-688-7175
>
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