[vtkusers] strange problem while creating a binary mask

[David Gobbi]

Hi Anja,

The vtkPolyDataToImageStencil calculates the normal of each polygon to 
find out which face of the polygon is the front (the "outside") and 
which is the back (the "inside").  The calculation of the normal depends 
on the ordering of the points.

You are extruding a polyline to create the the polydata, right?  
Unfortunately, I don't whether the the front/back orientation of the 
polygons depends on the ordering of points in the original polyline... 
Dean might have more experience here.

When you apply the stencil, most classes that have a SetStencil() method 
also have a ReverseStencilOn() method to set whether you want to use the 
region inside the stencil or the region outside the stencil.

 - David


Anja Ende wrote:
> Ok, I have clearly missed this part!!!
>
> So, the points have to be ordered in a counter clockwise fashion??? 
> Why is that???
>
> Cheers,
> Anja
>
> On 30/10/06, * Dean Inglis* <dean.inglis at sympatico.ca 
> <mailto:dean.inglis at sympatico.ca>> wrote:
>
>     Hi Anja,
>
>     is your polydata always defined such
>     that the points forming a closed loop are
>     ordered counter-clockwise or equivalently,
>     always clockwise and the vtkImageStencil set
>     accordingly?
>
>     Dean
>
>
>
>
>
> -- 
> Cheers,
>
> Anja
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