[vtk-developers] RE: [vtkusers] Useless triangulation in unstructured grid rendering

John Platt jcplatt at dsl.pipex.com
Wed Oct 11 11:04:29 EDT 2006


Knowing the filters exist is a problem but they are documented. I
suppose another possibility is to construct a helper class using these
filters - a bit like vtkDataSetMapper. The class could also manage a LUT
so the range can automatically be updated when new scalars arrive.

As for how you might implement such a change, presumably you would need
to store the input id of a cell/point for each output cell/point. When I
create UGrids, I only add point and cell field data ("node_numbers" and
"element_numbers"). These id's can then be used at any downstream stage
to get the required scalars. So, would I be paying for something I am
not using?

BTW I am with you 100% on the general principle of filters responding
more specifically to a change. But on the other hand, I prefer to keep
classes simple and well defined.


-----Original Message-----
From: John Biddiscombe [mailto:biddisco at cscs.ch] 
Sent: 11 October 2006 08:50
To: John Platt
Cc: vtk-developers at vtk.org
Subject: Re: [vtkusers] Useless triangulation in unstructured grid

> As you mentioned, vtkMergeFilter or vtkMergeDataObjectFilter >
> vtkAssignAttribute already allow you to separate the geometry and
> attribute data. So, is it worth the additional complexity and effort
> adding a new information key for this purpose?
The trouble is that these filters must be instantiated by the user - and

the user needs to "know" in advance that the pipeline has geometry 
unchanging. Adding an information key would allow filters which can take

advantage of it to bypass needless geometry recalculations 
(clip/cut/surface extraction/normal generation/many more etc) 
automatically without the user necessarily knowing that the geometry is 
fixed. Only the object generating the data need do anything.

It's a possibility I'd like to consider.


John Biddiscombe,                            email:biddisco @ cscs.ch
CSCS, Swiss National Supercomputing Centre  | Tel:  +41 (91) 610.82.07
Via Cantonale, 6928 Manno, Switzerland      | Fax:  +41 (91) 610.82.82

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