[vtkusers] More accurate clipping?

[John Norris]

Hi,

I'm using vtkClipDataSet with multiple functions combined using 
vtkImplicitBoolean.  This works well for the most part, but there are 
some too-common problems with this that I've been working on (so far 
unsuccessfully).

Consider the following case: a dataset is being clipped using two 
vtkPlanes objects, which are combined via a vtkImplicitBoolean object, 
and one cell has one point inside one vtkPlanes, and another point 
inside the other (see attached image #1).  I'd like the result to look 
like image #2, but it looks like image #3 instead.  I'm sure that 
vtkClipPolyData and vtkCutter suffer from similar problems.

My first attempt at a solution was a preconditioning filter.  This takes 
the clip function and breaks it down into a list of simple functions 
(vtkImplicitBoolean would be split into its subfunctions, vtkPlanes 
would be split into six vtkPlane objects, etc).  Then I loop through 
each function, and using the results of the previous iteration, I call 
each cell's Clip() method twice, once with insideOut set to 1.  This 
works, but it is extremely slow, even for a relatively simple clip 
function such as a single vtkPlanes object.  There must be a better way.

Has anyone done any work along these lines?

Thanks,
John
-- 
John Norris
Research Programmer
Center for Simulation of Advanced Rockets
http://www.uiuc.edu/ph/www/jnorris
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