[vtk-developers] implementing vtkPolyData::ComputeBounds() ?

[Lisa Sobierajski Avila]

Hi Sebastien,

I think it is more correct to have the vtkPolyData::ComputeBounds() 
implemented than to simply use the bounds of all points. Unless someone 
thinks this isn't the case, I would suggest implementing it, test it, then 
check it in - and we'll need to keep an eye on the timing for a few days to 
make sure it doesn't significantly slow anything down. I don't think it 
should since bounds only need to be recomputed when data is changed.


Lisa



At 12:49 PM 7/29/00, Sebastien BARRE wrote:
>Hi
>
>I was wondering why vtkPolyData::ComputeBounds() is not implemented ? Is 
>it OK if I take care of this ?
>
>Rational : suppose that given a polygonal object A, I use a 
>vtkClipPolyData filter to extract two other polygonal objects B, and C, 
>which will have different topologies (and most probably different extents).
>
>If I query the bounds of B and C using GetBounds(), or use vtkOulineFilter 
>to display very simple bounding boxes, I'll get ... the bounds of A. This 
>is no surprise because both A, B and C share the *same* points 
>(vtkPoints), and as A, B, C are vtkPolyData derived from vtkPointSet, 
>GetBounds() use vtkPointSet::ComputeBounds(), which computes the bounds by 
>iterating over the *points*.
>
>I'm a bit confused with that. If the only "visible" thing (or real data) 
>is defined in vtkPolyData by its cells, I guess ComputeBounds() should 
>reflect this too, am I right ?
>
>I used to circumvent the problem by defining a function in Tcl, but it's 
>soooooooo slow (GetCellsBounds() is not available in Tcl).
>
>Therefore, may I implement this vtkPolyData::ComputeBounds() feature ? The 
>bounds will be much more accurate. I'm asking first because GetBounds() is 
>used in so many files that I may have missed the "big picture".
>
>Thanks
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