How to extract surface from polydata

[mwestphal (Mathieu Westphal (Kitware))]

@at123 : please avoid asking the same question in multiple posts.

Problems using vtkContourWidget, vtkAppendPolyData, and vtkDelaunay3D

Hello, I have a ImageResliceVTKWidget. I can move across a series of medical images. Say I am moving from left to right between images. To create a contour on a certain image, I use the vtkContourWidget. I click multiple points and create a closed loop. First I create a large circle, then move to the right. Then I create a smaller circle. Then move to the right. Then create a large circle again. I would like to create a volume using these contours. So I use the vtkAppendPolyData. I do someth…