Hello again! I have found some possible solutions.
(1) It looks like that using the function described in topic 2530 it would be possible to extract an array of all the ids of the boundary nodes. In this case, I am still looking for a method to get the cell (triangles) ids and the edge ids (boundary edge of these triangles).
(2) Using vtkGeometryFilter() with options PassThroughCellIdsOn() and PassThroughPointIdsOn() might do the trick. However I am still looking for examples on how to use this to select boundary edges (topological dimension 1) of a triangulated surface (made of triangle cells). Actually, it is not clear to me what the input and output of vtkGeometryFilter() is, and what options I have to get what I need: points, edges and triangles along the boundary of a surface, all correlated (e.g. triangle A has boundary edge B with nodes C and D).
Thanks!