David,<br>You brought me into deep doubts (if plural exists for this noun...): I went back to vtkPolyData documentation (<a href="http://www.vtk.org/doc/nightly/html/classvtkPolyData.html#_details">http://www.vtk.org/doc/nightly/html/classvtkPolyData.html#_details</a>) and I noted that 0D, 1D and 2D cells are represented by separate vtkCellArray's. The flexibility you mention is better exposed in vtkUnstructuredGrid: <br>
<p><a class="el" href="http://www.vtk.org/doc/nightly/html/classvtkUnstructuredGrid.html" title="dataset represents arbitrary combinations of all possible cell types">"vtkUnstructuredGrid</a> is a data object that is a concrete implementation of <a class="el" href="http://www.vtk.org/doc/nightly/html/classvtkDataSet.html" title="abstract class to specify dataset behavior">vtkDataSet</a>. <a class="el" href="http://www.vtk.org/doc/nightly/html/classvtkUnstructuredGrid.html" title="dataset represents arbitrary combinations of all possible cell types">vtkUnstructuredGrid</a>
represents any combinations of any cell types. This includes 0D (e.g.,
points), 1D (e.g., lines, polylines), 2D (e.g., triangles, polygons),
and 3D (e.g., hexahedron, tetrahedron).".</p>Sorry for not confirming! Maybe a VTK developer could correct me if I misunderstood something...<br><br>Jerome<br><br><div class="gmail_quote">2009/12/11 David Doria <span dir="ltr"><<a href="mailto:daviddoria%2Bvtk@gmail.com">daviddoria+vtk@gmail.com</a>></span><br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="im">On Fri, Dec 11, 2009 at 4:45 AM, Jérôme <<a href="mailto:jerome.velut@gmail.com">jerome.velut@gmail.com</a>> wrote:<br>
> You are right, polydata is intended to describe 0D (vertices), 1D (lines)<br>
> and 2D (polygons) cell. Tetrahedrons are the "simplest" 3D cells, such as<br>
> triangles are the "simplest" 2D cells, but vtkPolyData cannot have 3D cells.<br>
> However, a tetrahedron is composed of 4 vertices, 6 edges (lines) and 4<br>
> triangles (polygons) that you can *represents* thanks to a vtkPolyData. when<br>
> you render a tetrahedral mesh through a polydata, you don't "see" the<br>
> tetrahedrons, but their bounds.<br>
><br>
><br>
> Jerome<br>
<br>
</div>Jerome -<br>
<br>
I'm not sure that is accurate - I believe the whole point of a<br>
polydata is that it is the most flexible data type in that it is the<br>
only one that DOES allow 3D cells. I'd have to double check the VTK<br>
book on that, but maybe someone else can verify this? I've been<br>
planing to add a brief description of each of these types to the wiki<br>
for a while so you may have motivated me to get around to it :)<br>
<br>
Thanks,<br>
<font color="#888888"><br>
David<br>
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