[vtkusers] surface area of plane

[John Platt]

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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