[vtkusers] Implicit functions rendering using an octree

[David.Pont at ForestResearch.co.nz]

Hi Jimmy,
   I had just started on a vtk class to 'polygonize' implicit functions,
based on an adaptive refinement algorithm. I hope to get something working
in a week or so (this is a part-time effort only). The algorithm has a nice
combination of speed and accuracy, with user control over accuracy.
Currently in vtk you have to sample implicit functions over a regular
volume and then contour. This new class will output polydata directly (it
uses cubes of different sizes too...) which should be much faster.

Just last week a user asked for a way of evaluating 'arbitrary' implicit
functions, so your work on that front sounds useful. How about you create a
class derived from vtkImplicitFunction that calls user defined callbacks
for EvaluateFunction and EvaluateGradient. I suggest you keep the parsing
etc within your application, although this might be useful too....! ?

I can work on the polygonizer unless you have the desire or the need to
solve this yourself. So at the end we will have two very useful vtk
classes.

    what do you think?
       Dave Pont


|--------+--------------------------------->
|        |          "Dimitris Andritsos"   |
|        |          <jimandr at hotmail.com>  |
|        |          Sent by:               |
|        |          vtkusers-admin at public.k|
|        |          itware.com             |
|        |                                 |
|        |                                 |
|        |          05/04/2003 19:46       |
|        |                                 |
|--------+--------------------------------->
  >------------------------------------------------------------------------------------------------------------|
  |                                                                                                            |
  |      To:     vtkusers at public.kitware.com                                                                   |
  |      cc:                                                                                                   |
  |      Subject:     [vtkusers] Implicit functions rendering using an octree                                  |
  >------------------------------------------------------------------------------------------------------------|




Hello everyone,

I am a new user to VTK and I would like your help. I am designing a
programm
that takes as input implicit functions (in the form of an equation), parses

and evaluates them. During the evaluation phase, an octree data structure
is
constructed and I want to use VTK to view the surface. How should this be
done?

I tried using marching cubes and although it works, because vtkImage data
have to be used, the number of evaluations is very big and the time it
takes
to render the surfaces is prohibitive. Can another type of data set be used

with the octree and marching cubes or any other contouring class of Vtk?
The
octree uses the cube as the basic voxel. The problem associated with the
octree, as I understand it, is that I end up with cubes of various sizes
and
this is why I can't use marching cubes.

I would really appreciate any help on this problem. It is not mandatory
that
I have to go with the octree so any other suggestion is welcome. I am
thinking of the octree for performance efficiency reasons.

Thanks a lot in advance,
Jimmy

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