[vtkusers] surface area of plane

[John Platt]

Hi Mark,

You could also look at vtkMassProperties but there is the general
assumption here that the polydata forms a closed surface. The area
calculation may still work though.

Merry Christmas also.

John.

-----Original Message-----
From: vtkusers-bounces+jcplatt=dsl.pipex.com at vtk.org
[mailto:vtkusers-bounces+jcplatt=dsl.pipex.com at vtk.org] On Behalf Of
Marc Christian Schöning
Sent: 22 December 2006 08:31
To: vtkusers at vtk.org
Cc: John Platt
Subject: Re: [vtkusers] surface area of plane

Hi John,

thanks very much for your ideas, i will give it a try.

Merry christmas,

Marc

John Platt wrote:
> Hi Marc,
>
> If you are cutting 3d cells, I thought you could find the area by ...
>
>  traverse the 2d cells in the output polydata from the cutter
>   get the cell : GetCell()
>   get the centre parametric coordinates : GetParametricCenter()
>   compute the inverse Jacobian matrix at this point :
JacobianInverse()
>   compute the determinant of the Jacobian (det J)
>   sum det J
>
> which could be extended to add a numerical integration loop for your
> point scalars. But unfortunately, JacobianInverse() is only
implemented
> for 3d cells.
>
> An alternative for the area is to sum the magnitude of the vector
> product of 2 adjacent edge vectors (1/2 value for triangles) but this
> does not extend for your scalars.
>
> If you are familiar with numerical integration, it would not be too
> difficult to implement an area scheme using, say, Gaussian
integration.
>
> HTH
>
> John.
>
> -----Original Message-----
> From: vtkusers-bounces+jcplatt=dsl.pipex.com at vtk.org
> [mailto:vtkusers-bounces+jcplatt=dsl.pipex.com at vtk.org] On Behalf Of
> Marc Christian Schöning
> Sent: 21 December 2006 07:44
> To: vtkusers at vtk.org
> Subject: [vtkusers] surface area of plane
>
> Hi guys,
>
> i need a possibility, to compute the surface area of a plane. the
plane 
> is produced by cutting a plane with an unstructured grid.
>
> vtk.UnstrucuredGrid -> vtkCutter (vtkPlane)
>
> First of all i would like to calculate the cutted surface area. 
> Furthermore, i would like to integrate the scalar solution, which is 
> also cutted from the unstructured grid.
>
> Any ideas,
>
> Thanks in advance
>
> Marc
>
>
>   


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