Not clear if you already have a triangulation. If not, there are an infinite number of ways to triangulate a vertex cloud; to define connectivity between vertices. If you only need to connect vertices on the boundary, computing the convex hull (QuickHull algorithm) probably makes most sense. If you want to allow concavities in the hull, you could insert vertices into a Delaunay triangulation.
Thanks QuickHull looks like a nice elegant solution but unfortunately wont work for the tins I am working with - they are tins of roads so imagine a loose 'J' shape. With QuickHull I'll end up having the end of the J joined to the start of the J I believe.
I'll look into Delaunay, at first glance it looks like this algorithm calculates all vertex connections/triangles and not just the boundary points? Is that correct?
Yes, the information I have is the triangulation and the vertices, thats the only information I have but not the boundary vertices or their connection order.