Note:

K = convexHull(DT)
[K AV] = convexHull(DT)
K = convexHull(DT)
returns the indices
into the array of points DT.X
that correspond to
the vertices of the convex hull.
[K AV] = convexHull(DT)
returns the convex
hull and the area or volume bounded by the convex hull.
DT  Delaunay triangulation. 
K  If the points lie in 2D space, K is a column
vector of length numf . Otherwise K is
a matrix of size numf byndim , numf being
the number of facets in the convex hull, and ndim the
dimension of the space where the points reside. 
AV  The area or volume of the convex hull. 
The convex hull of a set of points X
is the
smallest convex region containing all of the points of X
.
Compute the convex hull of a set of random points located within a unit square in 2D space.
x = rand(10,1) y = rand(10,1) dt = DelaunayTri(x,y) k = convexHull(dt) plot(dt.X(:,1),dt.X(:,2), '.', 'markersize',10); hold on; plot(dt.X(k,1),dt.X(k,2), 'r'); hold off;
Compute the convex hull of a set of random points located within a unit cube in 3D space, and the volume bounded by the convex hull.
X = rand(25,3) dt = DelaunayTri(X) [ch v] = convexHull(dt) trisurf(ch, dt.X(:,1),dt.X(:,2),dt.X(:,3), 'FaceColor', 'cyan')
convhull
 convhulln
 delaunayTriangulation
 triangulation
 voronoiDiagram