[vtkusers] get visible surface

Lodron, Gerald Gerald.Lodron at joanneum.at
Wed Aug 22 01:57:21 EDT 2012

Ok, thanks, i tested the vtkHardwareSelector in combination with the vtkExtractSelection Filter and have some questions:

-> In general it works well but always some "noisy" polygons outside the visible region remain, is there a way to remove them also? (I can give code examples/screenshots if necessary, data set is very huge to send but is possible if required)
-> The problem is that I will not have a monitor on my later device, so an offscreen like the mentioned osmesa is essential. Is this the  VTK_USE_OFFSCREENT flag in cmake? Are there any known troubles in that mode or does it work well (I use it on windows)?

Some details about my application:

A human walks with a special camera which makes depth images and records many frames of an object. From these depth images we generate a very huge image with propabilities of being  a surface (this is currently implemented and works). From this image we generate a vtkPolyData using the marching cubes (currently vtkMarchingCubes, but we will go to vtkSliceCubes because it can stream the input, later images will have a size of 10 000 x 10 000 x 10 000 which is about 4 Terrabyte, I do not have such a RAM so a streaming would be nice). The problem is that marching cubes always generates two surfaces of this floating PDF image, to remove the hidden one I want to use the camera position(s) with the hidden surface detection like the vtkHardwareSelector... So for every camera position I will call the HardwareSelector and will make a logical OR operation on the vtkInsidedness result of the vtkHardwareSelector... And I am afraid that the noisy remaining backtriangles of vtkHardwareSelector will accumulate...

Maybe someone has some hints for me...

-----Ursprüngliche Nachricht-----
Von: David E DeMarle [mailto:dave.demarle at kitware.com] 
Gesendet: Dienstag, 21. August 2012 20:19
An: David Doria
Cc: Lodron, Gerald; (vtkusers at vtk.org)
Betreff: Re: [vtkusers] get visible surface

Use this test as a start:

David E DeMarle
Kitware, Inc.
R&D Engineer
21 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-881-4909

On Tue, Aug 21, 2012 at 2:13 PM, David Doria <daviddoria at gmail.com> wrote:
> On Tue, Aug 21, 2012 at 1:47 PM, David E DeMarle 
> <dave.demarle at kitware.com>
> wrote:
>> Use vtkHardwareSelector, it is a more recent implementation of 
>> visible surface selection. It will give you cells if you ask it to 
>> for instance. See:
>> http://www.vtk.org/doc/nightly/html/classvtkHardwareSelector.html
>> I think the only thing that can be done about not needing a monitor 
>> is to use an offscreen rendering context (osmesa for example). Screen 
>> space operations like visible surface selection get too much from the 
>> infrastructure that VTK's display pipeline (and openGL underneath) 
>> provide to make removing them practical.
> If you figure out how to get it to work and could fix this example:
> http://www.vtk.org/Wiki/VTK/Examples/Cxx/Broken/Filtering/ExtractVisib
> leCells
> that would be great!
> David
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