[vtkusers] Line distance implicit function

David.Pont at ForestResearch.co.nz David.Pont at ForestResearch.co.nz
Mon Apr 7 19:35:17 EDT 2003

Hi Chris,
   I think you could use vtkImplicitModeller followed by vtkImplicitDataSet
but this is very inefficient. It seems vtkImplicitModeller is like
vtkImplicitFunction and vtkSampleFunction rolled up together. It would be
nice to unroll this: make a class derived from vtkImplicitFunction which
contains the EvaluatePosition stuff to get the distance functionality. You
might have to use local differences to get the gradient? Then you could
pass this new implicit function directly to the clipper. This sounds much
smarter, and a useful class.

   Dave Pont

|        |          Chris Scharver         |
|        |          <scharver at evl.uic.edu> |
|        |          Sent by:               |
|        |          vtkusers-admin at public.k|
|        |          itware.com             |
|        |                                 |
|        |                                 |
|        |          08/04/2003 09:44       |
|        |                                 |
  |                                                                                                            |
  |      To:     vtkusers at public.kitware.com                                                                   |
  |      cc:                                                                                                   |
  |      Subject:     [vtkusers] Line distance implicit function                                               |


I would like to use a distance function to clip some poly data. I
don't need to visualize the distance function, so vtkImplicitModeller
isn't quite what I want. However, it does seem to provide the core
functionality of sampling distance from a line. I want to use a
vtkImplicitFunction with vtkClipPolyData. The input is just a list of
lines, but I don't want the sampled volume since that would not match
with my polygon data. Do I need to create my own vtkImplicitFunction
from scratch, or is there something already available of which I can
take advantage?

Looking at vtkImplicitModeller.cxx, it seems like I may be able to
use vtkCell::EvaluatePosition() to take care of the work for me.
Would vtkPolyLine's implementation for that method correctly
determine an input point's distance from a given line? Or I am being
overly optimistic? :)

Chris Scharver
Electronic Visualization Laboratory
The University of Illinois at Chicago
Ph: 312-996-3002   FAX: 312-413-7585
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