- Which range of Alpha should I set ?
The alpha roughly drives the maximum edge length. As your point cloud seems to be quite dense, I would say something with 1 or 5% of the dataset size would seems good. If you choose Alpha too large, you may have large edges filling concavities. If you choose Alpha too small, you may have holes on the resulting meshes.
- How can I set Spacing For This ?
I am not sure to understand the question, can you clarify ?
- It take about 5 min to run!!! . What I should do to speed up?
A smaller Alpha may already improves the run time a bit, but not so much. There is no SMP on the VTK filter to improve running time neither so I do not see easy solutions. We could decimate the input but this would of course lead to bad quality result. We could try to use the efficient CGAL delaunay 3D implementation through vespa but this would require to implement it.