[vtkusers] How to get boundary polygon points from vtkPolyData?

[Larry]

Hello, everyone!
Say I have a vtkPolyData, which is in my case actually a bunch of triangle
cells lie on the same plane, now I want to get the boundary that enclose all
the triangles.

I tried CAG in java, generate one Area for each triangle, and UNION them
together, then extract the generalPath from the union area. But it sometimes
it doesn't work correctly.

Is there any way in vtk to do that?

Thanks!