[vtkusers] questions about vtk Marching Square filter

[Zhan Zhang]

Hi,

I have some questions about the vtk Marching Squares filter. 

Suppose I have a two-dimensional binary image, in which there is a
donut-like object. If I use marching square to extract the shape
boundary, I should get two circles (the inner and outer boundaries of
the donut-like object). I find that in the output file (vtk Poly Data
file) of the vtk marching square filter, the Cells Part are only line
cells---no polygons. In fact, what I am most interested in is the
connectivity lists of the points on these two boundaries, so I have to
generate these two point-lists (a point-list here represents one
circular boundary) by myself. 
1) Can anyone tell me whether VTK marching square provides such
functionality?
2) Suppose I have to generate such lists by myself strictly according
to the point connectivity indirectly given to me in the Line Cells Part
of the vtk Poly Data file, or suppose vtk can do this, my next question
is: suppose that in the binary image I traverse the calculated point
list representing the outer circle and that I look at my right hand side
and I always see "black", if I do the same thing on the second point
list representing the inner circle, will I always see "black" if
look at my right hand side? 

Hopefully I can get the answers. Thanks for reading this email.

Zhan