[vtkusers] Arbitrary cut plane

[Dai Shuo]

try the following steps:

Firstly, 
    you should know the original normal vector of your vtkPlaneSource,	
Secondly, 
	// get the transformation matrix of your PlaneSource after interaction
	double matrix[16];
    PlaneSourceActor->GetMatrix(matrix);	
Third,
    Multiplies the matrix and the original normal vector, 
	and the result is the current normal vector
	

>Hi!
>
>I am trying to cut an arbitrary plane in a volume. To do this I use
>vtkPlane and vtkCutter. I've managed to do cutting by selecting three
>points in the volume and computing the plane normals. The problem is that
>I would like to do the cutting by letting a user move a plane that
>intersects with the volume and then return the intersection. I have tried
>to do this by using vtkPlaneSource to draw a plane in the same window as
>the volume. The user can select an arbitrary centerpoint for rotation of
>the plane. After interaction I was hoping that I could extract the new
>plane normal and then use vtkPlane and vtkCutter to do the cutting in the
>same way as I did for the points, but I am not able to find the normals after
>interaction. Does anybody know how this can be done?
>
>Thank you in advance!
>
>Maria Ottermo
>
>
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　　　　　　　　Dai Shuo
　　　　　　　　dai_shuocn at 163.com
　　　　　　　　　　2002-06-05