Envelope is not (convex) hull 19:27 Nov 29, 2010
The convex hull of a given set is the smallest convex set containing the given set, that is the intersection of all convex sets (such as half-spaces)which contain the given set. The same term is also used to denote the outer surface of said hull. The convex hull need not be smooth.
An envelope of a family of differentiable manifolds is a differentiable manifold that is tangent to each member of the family (at some point). If the manifolds are one-dimensional, they are (smooth) curves; if two-dimensional, (smooth ordinary) surfaces. | 
The translation workplace 
