[vtkusers] Volume measurement

[Alyassin, Majeid M (CRD)]

Jennifer,

For a closed non-manifold surface, GetVolume & GetVolumeX,Y,Z all should return very similar answers.
But if the surface has openings along one direction the accuracy of GeVolume... along that direction
is affected.

   GetVolume = Kx * Volx + Ky * Voly + kz * Volz  where kx+ky+kz = 1.

    kx =  the number of maximum surface normals component along x  /  total surface normals.  

for more information about the details of this algorithm refer to a paper listed in the header of the
vtkMassProperty class.

So, if your rectangular block has an opening along one direction you may want to discard GetVolume...
or make sure you have closed surface first.  I believe the MassProperty.tcl examples calculates
several simple geometrical objects and one of which is a rectangular block (not 100 % sure...).


Hope this help

Majeid

-----Original Message-----
From: Jennifer Hare (CICC/HPC) <jen> [mailto:jen at ARL.MIL]
Sent: Friday, June 30, 2000 10:33 AM
To: vtkusers at public.kitware.com
Subject: Re: [vtkusers] Volume measurement



I posted this awhile ago and never received a response... 

Could someone please explain the difference between the following methods
in vtkMassProperties:

	GetVolume
	GetVolumeX
	GetVolumeY
	GetVolumeZ

I used GetVolume for a sphere and it returned the volume of that sphere.
I used GetVolume for a rectangular block, but it did not return the correct
volume of that block.  I then used GetVolumeZ for the rectangular block and 
it did return the correct volume of that block.  Does the method for finding
the volume depend on the data?  And if so, what are the dependencies?  I need
to find something (or need to write something) that will find the volume of 
any closed isosurface.

Thanks,

Jen

------------------------------------------------------------------------------
Jennifer J. Hare                   US Army Research Laboratory
Email: jen at arl.mil       Computational and Information Sciences Directorate
Phone: 410.278.9149            High Performance Computing Division
Fax: 410.278.9199                 Scientific Visualization Team
------------------------------------------------------------------------------

On Fri, 30 Jun 2000, Will Schroeder wrote:

> Hi Andre-
> 
> The class vtk/contrib/vtkMassProperties.h does this. Look in contrib/examplesTcl/MassProperties.tcl
for an example.
> Note: the surface must be closed (and manifold) for this to work.
> 
> Will
> 
> At 10:56 AM 6/30/00 -0300, Andre Domingos A. Souza wrote:
> >Dear VTK Users,
> >
> >I would like to calculate the volume of polygonal model created using
> >vtkMarchingCubes. Could someone please post a Tcl script?
> >
> >Thank you,
> >
> >Andre
> 
> 
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