[vtkusers] Confussion using MarchingSquares

[Mauricio Reyes]

 Hi vtk users, am a student of engineering am I starting with VTK, I
have a question about MarchingSquares (or MarchingCubes) .
 Well, I read that the alghorithm analyze every cell for the processing
of find the isocontour (or isosourface), but my confussion is this:  in
the 2D case, the cell is a square, so , it is composed by 4 corners,
now, in a image this corners are the value of the pixels ?, because in
that case I will need 4 pixeles to create a cell, is that true? and if
that is true the SetDataSpacing especify the spacing among pixels?

I have a terrible confussion with the relation:  image-pixel and cell.

thanks in advance...
Mauricio Reyes