How to calculate the area of Alpha _ shape _ 2 or Alpha _ shape _ 3?

[Kasi]

How to calculate the area of Alpha _ shape _ 2 or Alpha _ shape _ 3?

[stla]

What do you mean by the area for the 3D case? The area of the surface? You can make a mesh with the alpha shape and there's a function in CGAL to get the area of the surface of a 3D mesh.

[stla]

Your questions are not understandable. Please make an effort to be clearer. I don't know what you're talking about.

[Kasi]

Sorry, English is not my mother tongue. I am using the translation software.

[Kasi]

I set the alpha value solved the problem that the volume of alpha shape equals the volume of convex hull.
as.set_alpha(1.0)

Why do I need to set the alpha value?

[sloriot]

I don't know what is your shape but for any shape, there exists a value of alpha such that the alpha shape is actually the convex hull. So it might be that 1 is larger or equal to that value for your shape.

[stla]

Why do I need to set the alpha value?

The alpha shape depends on a parameter alpha. Take a look at the documentation. When the alpha value is big enough, the alpha shape is the convex hull. You don't visualize your meshes?