[vtk-developers] vtkOBBTree vtkPoints vs vtkPolyData on the input

[John Biddiscombe]

Is it possible that what you are seeing is the consequence of having a 
vtkPolyData object with a lot of unused points. When you pass the cells 
in, only those point that are being used by cells go towards the tree, 
whereas when you pass the entire point list in with no cells, all are 
considered.

JB
> Hi all,
>
> I am having some strange results when using the vtkOBBTree. I am using 
> only the method ComputeOBB. I had been passing polydata through 
> however had recently switched to passing through only the points, as 
> sometimes the polydata was too large to fit in the memory of a single 
> compute node.  I have noticed that when I call ComputeOBB with a 
> vtkPoints I get a drastically different OBB than when I call it with a 
> vtkPolyData. For example http://quaoar.sr.unh.edu/obb/bigObb.png the 
> white surface is the OBB that results from passing the points of the 
> red dataset through the OBB filter. When I use the polydata I get an 
> OBB that tightly fits the input data set. I expect in both cases 
> (vtkPoints/vtkPolyData) to get a tightly fitting OBB since the input 
> is an axis aligned box itself. Is this expected behavior? Why would 
> the results differ so drastically?
>
> Thanks in advance
> Burlen
>


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