Deduce concave or convex

Hi,

I'm trying to determine the curvature of a point cloud. At the moment I have finde a way to compute de normals and the curvature thanks a PCA analysis but now I'm trying to automatic identify if the portion of the point cloud with maximum curvature (red) is concave or convex. Any idea how to deduce that with the normals vectors (green)?

Thank you.