[vtkusers] Visualisation non linear cells

[John Platt]

Hi Soeren,

I am no expert in VTK but I have used nonlinear cells and also wish to
extend the types available. These are some comments based on what I have
seen in the code rather than experience implementing a new cell type.

Triangulate() is used by surface filters (vtkDataSetSurfaceFilter) to
replace quadratic faces by linear triangles. The schemes are carefully
chosen so as NOT to introduce new points. Implementing a new scheme with
more points to give better resolution of curved edges will require some
care to ensure adjacent edges detect the new points. The point data must
also be interpolated. It may also be necessary to make Subdivide()
compatible with Triangulate().

In version 4.4 there does not appear to be any concrete implementations
of Tesselate(). Have you looked at?

http://www.vtk.org/doc/nightly/html/classvtkGenericCellTessellator.html

HTH

John.

-----Original Message-----
From: vtkusers-bounces at vtk.org [mailto:vtkusers-bounces at vtk.org] On
Behalf Of Soeren Gebbert
Sent: 13 January 2005 15:40
To: vtkusers at vtk.org
Subject: [vtkusers] Visualisation non linear cells

Dear vtkusers and developers,
I'm using vtk 4.4 and paraview 1.8.2 at linux and windows. I'm a
beginner
in vtk but i have some important questions to ask:

I want to add new nonlinear celltypes to vtk, like a quadratic quad with
an area center point and so on.
And i want to visualize them with a curved surface. Since now i used
paraview to visualize
the already implemented quadratic celltypes (QuadraticTetra ...). In
paraview i used the TempTessellatorFilter to get
a proper visualisation. I thought this filter is also implementet in vtk
but it isnt. So i searched for a
proper functionality in vtk to get my curved surface, but i didnt found
a filter.

As it is described in the vtk books, the quadratic cells will be
visualized as linear cells.
I guess the reimplemented function "Triangulate" from vtkCell in the in
the vtkNonLineareCell classes is doing this.
But there is a virtual function named Tesselate declrated in
vtkNonLinearCell, i guess this function will be used to render curved
surfaces, but this function is not implemented yet. So my question is:

1.) Is the function "Triangulate" responsible for the visualisation of
the different celltypes in vtk?
2.) If 1. is ture, can i reimplement the Triangulate function to create
curved surfaces for nonlineare cells?
3.) Is it possible to reimplement the "Tesselate" function and use this
for visualisation of nonlinear cells?
4.) If 1. - 3. is not true, what can i do to visualize 2D and 3D
nonlinear cells to get the form that is described
     in the shape function of these cells?

Thanks alot and best regards
Soeren Gebbert

btw.:
Please excuse my english.

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