How to detect boundary points

Question

I have a set of points in a 2D plane. I need to detect only the points that belong to the shape that borns from the union of this subset of points in order to cover the largest area: that is, the boundary points.

The following figure is an example:

The red points are those ones I need to detect.

Answer 1

What you need is called Convex hull . A lot of algorithms exist to calculate it.