[vtk-developers] Polyhedral challenge

[Mark Olesen]

On Tue, 2010-02-23 at 12:13 -0500, Will Schroeder wrote:
> The third method below is implemented and supports polyhedron.
> Comments welcome.
> 
> 
>   // Description:
>   // Insert/create cell in object by type and list of point ids
> defining
>   // cell topology. Most cells require just a type which implicitly
> defines
>   // a set of points and their ordering. However, some cells like
>   // vtkPolyhedron require points plus a list of faces. Note when
> inserting
>   // faces, the standard vtkCellArray format is assumed
> (n,i,j,k,n,i,j,k,...).
>   vtkIdType InsertNextCell(int type, vtkIdType npts, vtkIdType *pts);
>   vtkIdType InsertNextCell(int type, vtkIdList *ptIds);
>   vtkIdType InsertNextCell(int type, vtkIdType npts, vtkIdType
> *ptIds, 
>                            vtkIdType nfaces, vtkIdType *faces);

Thanks for the information!

This is a little nitpicking, but I'd suggest the third parameter be
named '*pts' instead of '*ptIds' for consistent naming of this parameter
type (vtkIdType vs. vtkIdList). Also, the comment 

// the standard vtkCellArray format is assumed (n,id1,id2,...,idn,
n,id1,id2,...,idn, ...) might be less confusing than with i,j,k.



If I understand the vtkPolyhedron insertion method correctly, the
'*pts' (or '*ptIds') would be a list of the _unique_ points used by the
cell and specified as global point indices whereas the '*faces' contains
local addressing.

In general this makes sense, however, it would also be extremely
convenient for the end-user if the first InsertNextCell() method could
also be used directly for polyhedra. This would greatly simplify the
end-user coding and perhaps avoid code repetition.

In this case the 'npts' and '*pts' parameters of
    InsertNextCell(int type, vtkIdType npts, vtkIdType *pts)
would represent the number of faces and the face-stream, respectively,
The face stream would be in the standard vtkCellArray format, but with
global point ids.


I've attached a pseudo-code example to illustrate what I mean.
Please let me know what you think.

/mark



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