[vtkusers] Seed landmark on 2D CT image

[John Drescher]

> For applying ITK segmentation algorithm, interactive seed picking is needed.
> Thus the vtkSeedWidget and vtkPointHandleRepresentation2D are used to put
> landmarks on the 2D CT image. For navigation between different CT image
> slices, the vtkSliderRepresentation2D is utilized.
>
>
>
> The problem is that the previous landmarks marked on a previous image slice
> also appear on the current slice. How to make the previously marked
> landmarks stay on that image slice only?
>

For my application I retained a list of seeds per slice and swapped
the list out when the slice changed.

John