[vtkusers] Cell data in a vtkPolyData object

[John Platt]

Hi Charles,

Could you use vtkUnstructuredGrid for your cells and convert to
vtkPolyData when all data is ready for rendering? There are no separate
cell arrays so you can always work with a cellId. Obviously there will
be a hit on performance but it may be worth considering.

Your query generated a great response and it would be a pity if this
knowledge could not be harnessed to at least a point where a solution
was formulated. You never know, someone may even attempt an
implementation! A starting point could be - how could
vtkUnstructuredGrid be specialized to polydata to give the required
traversal speed of vtkPolyData?

Even the FE users don't have it all their own way when it comes to data
- we would like point values for each cell!

John.

-----Original Message-----
From: vtkusers-bounces at vtk.org [mailto:vtkusers-bounces at vtk.org] On
Behalf Of Charles Boivin
Sent: 27 August 2004 20:32
To: niemeijer at science-and-technology.nl;
jbiddiscombe at skippingmouse.co.uk
Cc: vtkusers at vtk.org; clinton at elemtech.com
Subject: Re: [vtkusers] Cell data in a vtkPolyData object

Thanks to everyone who answered my original question on cell data in a
vtkPolyData object (Sander, John, and Clinton). I could not expect my
question would generate such a thread but it has been very informative.

I am glad to see that what I was basically coming to believe was
happening is *really* happening. I must admit it is a bit of a let-down.
I've seen this happen before -- it seems like cell data is very much an
afterthought in visualization software. AVS, for example, has an awful
support for it; most algorithms expect node data. Sure, node data is
great for FE people, but when you're dealing with FV methods, what you
are really interested in is cell data (at least I am!)

However, there *is* a workaround, provided you know which mapper you
are using, so I believe that that is the approach I will be taking. I
will do some more bookkeeping as I am reading my data and will make sure
I order things properly for the cell data. I still believe this should
be happening "under the hood", but I'll just live with it for now... 

Thanks to everyone for your expertise, it has been really helpful.

Charles Boivin
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